diff --git a/lib/std/os/uefi.zig b/lib/std/os/uefi.zig
index 7c6eb08a93c1..7e2f4367d8e6 100644
--- a/lib/std/os/uefi.zig
+++ b/lib/std/os/uefi.zig
@@ -23,6 +23,12 @@ pub var system_table: *tables.SystemTable = undefined;
 /// A handle to an event structure.
 pub const Event = *opaque {};
 
+/// The calling convention used for all external functions part of the UEFI API.
+pub const cc = switch (@import("builtin").target.cpu.arch) {
+    .x86_64 => .Win64,
+    else => .C,
+};
+
 pub const MacAddress = extern struct {
     address: [32]u8,
 };
diff --git a/lib/std/os/uefi/protocols/absolute_pointer_protocol.zig b/lib/std/os/uefi/protocols/absolute_pointer_protocol.zig
index ecf44eb26c93..ed9a1ed20aa4 100644
--- a/lib/std/os/uefi/protocols/absolute_pointer_protocol.zig
+++ b/lib/std/os/uefi/protocols/absolute_pointer_protocol.zig
@@ -3,11 +3,12 @@ const uefi = std.os.uefi;
 const Event = uefi.Event;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Protocol for touchscreens
 pub const AbsolutePointerProtocol = extern struct {
-    _reset: *const fn (*const AbsolutePointerProtocol, bool) callconv(.C) Status,
-    _get_state: *const fn (*const AbsolutePointerProtocol, *AbsolutePointerState) callconv(.C) Status,
+    _reset: *const fn (*const AbsolutePointerProtocol, bool) callconv(cc) Status,
+    _get_state: *const fn (*const AbsolutePointerProtocol, *AbsolutePointerState) callconv(cc) Status,
     wait_for_input: Event,
     mode: *AbsolutePointerMode,
 
diff --git a/lib/std/os/uefi/protocols/block_io_protocol.zig b/lib/std/os/uefi/protocols/block_io_protocol.zig
index ce5069d19f09..cdbc7a184259 100644
--- a/lib/std/os/uefi/protocols/block_io_protocol.zig
+++ b/lib/std/os/uefi/protocols/block_io_protocol.zig
@@ -1,6 +1,7 @@
 const std = @import("std");
 const uefi = std.os.uefi;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const EfiBlockMedia = extern struct {
     /// The current media ID. If the media changes, this value is changed.
@@ -44,10 +45,10 @@ pub const BlockIoProtocol = extern struct {
     revision: u64,
     media: *EfiBlockMedia,
 
-    _reset: *const fn (*BlockIoProtocol, extended_verification: bool) callconv(.C) Status,
-    _read_blocks: *const fn (*BlockIoProtocol, media_id: u32, lba: u64, buffer_size: usize, buf: [*]u8) callconv(.C) Status,
-    _write_blocks: *const fn (*BlockIoProtocol, media_id: u32, lba: u64, buffer_size: usize, buf: [*]u8) callconv(.C) Status,
-    _flush_blocks: *const fn (*BlockIoProtocol) callconv(.C) Status,
+    _reset: *const fn (*BlockIoProtocol, extended_verification: bool) callconv(cc) Status,
+    _read_blocks: *const fn (*BlockIoProtocol, media_id: u32, lba: u64, buffer_size: usize, buf: [*]u8) callconv(cc) Status,
+    _write_blocks: *const fn (*BlockIoProtocol, media_id: u32, lba: u64, buffer_size: usize, buf: [*]u8) callconv(cc) Status,
+    _flush_blocks: *const fn (*BlockIoProtocol) callconv(cc) Status,
 
     /// Resets the block device hardware.
     pub fn reset(self: *Self, extended_verification: bool) Status {
diff --git a/lib/std/os/uefi/protocols/edid_override_protocol.zig b/lib/std/os/uefi/protocols/edid_override_protocol.zig
index bbae0563cc37..33a4015f9f8d 100644
--- a/lib/std/os/uefi/protocols/edid_override_protocol.zig
+++ b/lib/std/os/uefi/protocols/edid_override_protocol.zig
@@ -3,10 +3,11 @@ const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const Handle = uefi.Handle;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Override EDID information
 pub const EdidOverrideProtocol = extern struct {
-    _get_edid: *const fn (*const EdidOverrideProtocol, Handle, *EdidOverrideProtocolAttributes, *usize, *?[*]u8) callconv(.C) Status,
+    _get_edid: *const fn (*const EdidOverrideProtocol, Handle, *EdidOverrideProtocolAttributes, *usize, *?[*]u8) callconv(cc) Status,
 
     /// Returns policy information and potentially a replacement EDID for the specified video output device.
     pub fn getEdid(
diff --git a/lib/std/os/uefi/protocols/file_protocol.zig b/lib/std/os/uefi/protocols/file_protocol.zig
index 53ec5f81e37e..8ff0a82701b2 100644
--- a/lib/std/os/uefi/protocols/file_protocol.zig
+++ b/lib/std/os/uefi/protocols/file_protocol.zig
@@ -4,19 +4,20 @@ const io = std.io;
 const Guid = uefi.Guid;
 const Time = uefi.Time;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const FileProtocol = extern struct {
     revision: u64,
-    _open: *const fn (*const FileProtocol, **const FileProtocol, [*:0]const u16, u64, u64) callconv(.C) Status,
-    _close: *const fn (*const FileProtocol) callconv(.C) Status,
-    _delete: *const fn (*const FileProtocol) callconv(.C) Status,
-    _read: *const fn (*const FileProtocol, *usize, [*]u8) callconv(.C) Status,
-    _write: *const fn (*const FileProtocol, *usize, [*]const u8) callconv(.C) Status,
-    _get_position: *const fn (*const FileProtocol, *u64) callconv(.C) Status,
-    _set_position: *const fn (*const FileProtocol, u64) callconv(.C) Status,
-    _get_info: *const fn (*const FileProtocol, *align(8) const Guid, *const usize, [*]u8) callconv(.C) Status,
-    _set_info: *const fn (*const FileProtocol, *align(8) const Guid, usize, [*]const u8) callconv(.C) Status,
-    _flush: *const fn (*const FileProtocol) callconv(.C) Status,
+    _open: *const fn (*const FileProtocol, **const FileProtocol, [*:0]const u16, u64, u64) callconv(cc) Status,
+    _close: *const fn (*const FileProtocol) callconv(cc) Status,
+    _delete: *const fn (*const FileProtocol) callconv(cc) Status,
+    _read: *const fn (*const FileProtocol, *usize, [*]u8) callconv(cc) Status,
+    _write: *const fn (*const FileProtocol, *usize, [*]const u8) callconv(cc) Status,
+    _get_position: *const fn (*const FileProtocol, *u64) callconv(cc) Status,
+    _set_position: *const fn (*const FileProtocol, u64) callconv(cc) Status,
+    _get_info: *const fn (*const FileProtocol, *align(8) const Guid, *const usize, [*]u8) callconv(cc) Status,
+    _set_info: *const fn (*const FileProtocol, *align(8) const Guid, usize, [*]const u8) callconv(cc) Status,
+    _flush: *const fn (*const FileProtocol) callconv(cc) Status,
 
     pub const SeekError = error{SeekError};
     pub const GetSeekPosError = error{GetSeekPosError};
diff --git a/lib/std/os/uefi/protocols/graphics_output_protocol.zig b/lib/std/os/uefi/protocols/graphics_output_protocol.zig
index 3b1cb1f417dd..43be507b79bd 100644
--- a/lib/std/os/uefi/protocols/graphics_output_protocol.zig
+++ b/lib/std/os/uefi/protocols/graphics_output_protocol.zig
@@ -2,12 +2,13 @@ const std = @import("std");
 const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Graphics output
 pub const GraphicsOutputProtocol = extern struct {
-    _query_mode: *const fn (*const GraphicsOutputProtocol, u32, *usize, **GraphicsOutputModeInformation) callconv(.C) Status,
-    _set_mode: *const fn (*const GraphicsOutputProtocol, u32) callconv(.C) Status,
-    _blt: *const fn (*const GraphicsOutputProtocol, ?[*]GraphicsOutputBltPixel, GraphicsOutputBltOperation, usize, usize, usize, usize, usize, usize, usize) callconv(.C) Status,
+    _query_mode: *const fn (*const GraphicsOutputProtocol, u32, *usize, **GraphicsOutputModeInformation) callconv(cc) Status,
+    _set_mode: *const fn (*const GraphicsOutputProtocol, u32) callconv(cc) Status,
+    _blt: *const fn (*const GraphicsOutputProtocol, ?[*]GraphicsOutputBltPixel, GraphicsOutputBltOperation, usize, usize, usize, usize, usize, usize, usize) callconv(cc) Status,
     mode: *GraphicsOutputProtocolMode,
 
     /// Returns information for an available graphics mode that the graphics device and the set of active video output devices supports.
diff --git a/lib/std/os/uefi/protocols/hii_database_protocol.zig b/lib/std/os/uefi/protocols/hii_database_protocol.zig
index 7538d6afd14a..179a93a73c92 100644
--- a/lib/std/os/uefi/protocols/hii_database_protocol.zig
+++ b/lib/std/os/uefi/protocols/hii_database_protocol.zig
@@ -3,14 +3,15 @@ const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
 const hii = uefi.protocols.hii;
+const cc = uefi.cc;
 
 /// Database manager for HII-related data structures.
 pub const HIIDatabaseProtocol = extern struct {
     _new_package_list: Status, // TODO
-    _remove_package_list: *const fn (*const HIIDatabaseProtocol, hii.HIIHandle) callconv(.C) Status,
-    _update_package_list: *const fn (*const HIIDatabaseProtocol, hii.HIIHandle, *const hii.HIIPackageList) callconv(.C) Status,
-    _list_package_lists: *const fn (*const HIIDatabaseProtocol, u8, ?*const Guid, *usize, [*]hii.HIIHandle) callconv(.C) Status,
-    _export_package_lists: *const fn (*const HIIDatabaseProtocol, ?hii.HIIHandle, *usize, *hii.HIIPackageList) callconv(.C) Status,
+    _remove_package_list: *const fn (*const HIIDatabaseProtocol, hii.HIIHandle) callconv(cc) Status,
+    _update_package_list: *const fn (*const HIIDatabaseProtocol, hii.HIIHandle, *const hii.HIIPackageList) callconv(cc) Status,
+    _list_package_lists: *const fn (*const HIIDatabaseProtocol, u8, ?*const Guid, *usize, [*]hii.HIIHandle) callconv(cc) Status,
+    _export_package_lists: *const fn (*const HIIDatabaseProtocol, ?hii.HIIHandle, *usize, *hii.HIIPackageList) callconv(cc) Status,
     _register_package_notify: Status, // TODO
     _unregister_package_notify: Status, // TODO
     _find_keyboard_layouts: Status, // TODO
diff --git a/lib/std/os/uefi/protocols/hii_popup_protocol.zig b/lib/std/os/uefi/protocols/hii_popup_protocol.zig
index d73af9d8eb1e..d695df29006a 100644
--- a/lib/std/os/uefi/protocols/hii_popup_protocol.zig
+++ b/lib/std/os/uefi/protocols/hii_popup_protocol.zig
@@ -3,11 +3,12 @@ const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
 const hii = uefi.protocols.hii;
+const cc = uefi.cc;
 
 /// Display a popup window
 pub const HIIPopupProtocol = extern struct {
     revision: u64,
-    _create_popup: *const fn (*const HIIPopupProtocol, HIIPopupStyle, HIIPopupType, hii.HIIHandle, u16, ?*HIIPopupSelection) callconv(.C) Status,
+    _create_popup: *const fn (*const HIIPopupProtocol, HIIPopupStyle, HIIPopupType, hii.HIIHandle, u16, ?*HIIPopupSelection) callconv(cc) Status,
 
     /// Displays a popup window.
     pub fn createPopup(self: *const HIIPopupProtocol, style: HIIPopupStyle, popup_type: HIIPopupType, handle: hii.HIIHandle, msg: u16, user_selection: ?*HIIPopupSelection) Status {
diff --git a/lib/std/os/uefi/protocols/ip6_config_protocol.zig b/lib/std/os/uefi/protocols/ip6_config_protocol.zig
index a4f370e406e8..27ee360a0dcd 100644
--- a/lib/std/os/uefi/protocols/ip6_config_protocol.zig
+++ b/lib/std/os/uefi/protocols/ip6_config_protocol.zig
@@ -3,12 +3,13 @@ const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const Event = uefi.Event;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const Ip6ConfigProtocol = extern struct {
-    _set_data: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, usize, *const anyopaque) callconv(.C) Status,
-    _get_data: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, *usize, ?*const anyopaque) callconv(.C) Status,
-    _register_data_notify: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, Event) callconv(.C) Status,
-    _unregister_data_notify: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, Event) callconv(.C) Status,
+    _set_data: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, usize, *const anyopaque) callconv(cc) Status,
+    _get_data: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, *usize, ?*const anyopaque) callconv(cc) Status,
+    _register_data_notify: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, Event) callconv(cc) Status,
+    _unregister_data_notify: *const fn (*const Ip6ConfigProtocol, Ip6ConfigDataType, Event) callconv(cc) Status,
 
     pub fn setData(self: *const Ip6ConfigProtocol, data_type: Ip6ConfigDataType, data_size: usize, data: *const anyopaque) Status {
         return self._set_data(self, data_type, data_size, data);
diff --git a/lib/std/os/uefi/protocols/ip6_protocol.zig b/lib/std/os/uefi/protocols/ip6_protocol.zig
index 4b106c7d9703..e734411be902 100644
--- a/lib/std/os/uefi/protocols/ip6_protocol.zig
+++ b/lib/std/os/uefi/protocols/ip6_protocol.zig
@@ -6,17 +6,18 @@ const Status = uefi.Status;
 const MacAddress = uefi.protocols.MacAddress;
 const ManagedNetworkConfigData = uefi.protocols.ManagedNetworkConfigData;
 const SimpleNetworkMode = uefi.protocols.SimpleNetworkMode;
+const cc = uefi.cc;
 
 pub const Ip6Protocol = extern struct {
-    _get_mode_data: *const fn (*const Ip6Protocol, ?*Ip6ModeData, ?*ManagedNetworkConfigData, ?*SimpleNetworkMode) callconv(.C) Status,
-    _configure: *const fn (*const Ip6Protocol, ?*const Ip6ConfigData) callconv(.C) Status,
-    _groups: *const fn (*const Ip6Protocol, bool, ?*const Ip6Address) callconv(.C) Status,
-    _routes: *const fn (*const Ip6Protocol, bool, ?*const Ip6Address, u8, ?*const Ip6Address) callconv(.C) Status,
-    _neighbors: *const fn (*const Ip6Protocol, bool, *const Ip6Address, ?*const MacAddress, u32, bool) callconv(.C) Status,
-    _transmit: *const fn (*const Ip6Protocol, *Ip6CompletionToken) callconv(.C) Status,
-    _receive: *const fn (*const Ip6Protocol, *Ip6CompletionToken) callconv(.C) Status,
-    _cancel: *const fn (*const Ip6Protocol, ?*Ip6CompletionToken) callconv(.C) Status,
-    _poll: *const fn (*const Ip6Protocol) callconv(.C) Status,
+    _get_mode_data: *const fn (*const Ip6Protocol, ?*Ip6ModeData, ?*ManagedNetworkConfigData, ?*SimpleNetworkMode) callconv(cc) Status,
+    _configure: *const fn (*const Ip6Protocol, ?*const Ip6ConfigData) callconv(cc) Status,
+    _groups: *const fn (*const Ip6Protocol, bool, ?*const Ip6Address) callconv(cc) Status,
+    _routes: *const fn (*const Ip6Protocol, bool, ?*const Ip6Address, u8, ?*const Ip6Address) callconv(cc) Status,
+    _neighbors: *const fn (*const Ip6Protocol, bool, *const Ip6Address, ?*const MacAddress, u32, bool) callconv(cc) Status,
+    _transmit: *const fn (*const Ip6Protocol, *Ip6CompletionToken) callconv(cc) Status,
+    _receive: *const fn (*const Ip6Protocol, *Ip6CompletionToken) callconv(cc) Status,
+    _cancel: *const fn (*const Ip6Protocol, ?*Ip6CompletionToken) callconv(cc) Status,
+    _poll: *const fn (*const Ip6Protocol) callconv(cc) Status,
 
     /// Gets the current operational settings for this instance of the EFI IPv6 Protocol driver.
     pub fn getModeData(self: *const Ip6Protocol, ip6_mode_data: ?*Ip6ModeData, mnp_config_data: ?*ManagedNetworkConfigData, snp_mode_data: ?*SimpleNetworkMode) Status {
diff --git a/lib/std/os/uefi/protocols/ip6_service_binding_protocol.zig b/lib/std/os/uefi/protocols/ip6_service_binding_protocol.zig
index fc56249c5504..d26173800457 100644
--- a/lib/std/os/uefi/protocols/ip6_service_binding_protocol.zig
+++ b/lib/std/os/uefi/protocols/ip6_service_binding_protocol.zig
@@ -3,10 +3,11 @@ const uefi = std.os.uefi;
 const Handle = uefi.Handle;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const Ip6ServiceBindingProtocol = extern struct {
-    _create_child: *const fn (*const Ip6ServiceBindingProtocol, *?Handle) callconv(.C) Status,
-    _destroy_child: *const fn (*const Ip6ServiceBindingProtocol, Handle) callconv(.C) Status,
+    _create_child: *const fn (*const Ip6ServiceBindingProtocol, *?Handle) callconv(cc) Status,
+    _destroy_child: *const fn (*const Ip6ServiceBindingProtocol, Handle) callconv(cc) Status,
 
     pub fn createChild(self: *const Ip6ServiceBindingProtocol, handle: *?Handle) Status {
         return self._create_child(self, handle);
diff --git a/lib/std/os/uefi/protocols/loaded_image_protocol.zig b/lib/std/os/uefi/protocols/loaded_image_protocol.zig
index 97dfe138b847..925cd4c46de0 100644
--- a/lib/std/os/uefi/protocols/loaded_image_protocol.zig
+++ b/lib/std/os/uefi/protocols/loaded_image_protocol.zig
@@ -6,6 +6,7 @@ const Status = uefi.Status;
 const SystemTable = uefi.tables.SystemTable;
 const MemoryType = uefi.tables.MemoryType;
 const DevicePathProtocol = uefi.protocols.DevicePathProtocol;
+const cc = uefi.cc;
 
 pub const LoadedImageProtocol = extern struct {
     revision: u32,
@@ -20,7 +21,7 @@ pub const LoadedImageProtocol = extern struct {
     image_size: u64,
     image_code_type: MemoryType,
     image_data_type: MemoryType,
-    _unload: *const fn (*const LoadedImageProtocol, Handle) callconv(.C) Status,
+    _unload: *const fn (*const LoadedImageProtocol, Handle) callconv(cc) Status,
 
     /// Unloads an image from memory.
     pub fn unload(self: *const LoadedImageProtocol, handle: Handle) Status {
diff --git a/lib/std/os/uefi/protocols/managed_network_protocol.zig b/lib/std/os/uefi/protocols/managed_network_protocol.zig
index 5ea63f5a658a..3dca6f510357 100644
--- a/lib/std/os/uefi/protocols/managed_network_protocol.zig
+++ b/lib/std/os/uefi/protocols/managed_network_protocol.zig
@@ -6,16 +6,17 @@ const Status = uefi.Status;
 const Time = uefi.Time;
 const SimpleNetworkMode = uefi.protocols.SimpleNetworkMode;
 const MacAddress = uefi.protocols.MacAddress;
+const cc = uefi.cc;
 
 pub const ManagedNetworkProtocol = extern struct {
-    _get_mode_data: *const fn (*const ManagedNetworkProtocol, ?*ManagedNetworkConfigData, ?*SimpleNetworkMode) callconv(.C) Status,
-    _configure: *const fn (*const ManagedNetworkProtocol, ?*const ManagedNetworkConfigData) callconv(.C) Status,
-    _mcast_ip_to_mac: *const fn (*const ManagedNetworkProtocol, bool, *const anyopaque, *MacAddress) callconv(.C) Status,
-    _groups: *const fn (*const ManagedNetworkProtocol, bool, ?*const MacAddress) callconv(.C) Status,
-    _transmit: *const fn (*const ManagedNetworkProtocol, *const ManagedNetworkCompletionToken) callconv(.C) Status,
-    _receive: *const fn (*const ManagedNetworkProtocol, *const ManagedNetworkCompletionToken) callconv(.C) Status,
-    _cancel: *const fn (*const ManagedNetworkProtocol, ?*const ManagedNetworkCompletionToken) callconv(.C) Status,
-    _poll: *const fn (*const ManagedNetworkProtocol) callconv(.C) Status,
+    _get_mode_data: *const fn (*const ManagedNetworkProtocol, ?*ManagedNetworkConfigData, ?*SimpleNetworkMode) callconv(cc) Status,
+    _configure: *const fn (*const ManagedNetworkProtocol, ?*const ManagedNetworkConfigData) callconv(cc) Status,
+    _mcast_ip_to_mac: *const fn (*const ManagedNetworkProtocol, bool, *const anyopaque, *MacAddress) callconv(cc) Status,
+    _groups: *const fn (*const ManagedNetworkProtocol, bool, ?*const MacAddress) callconv(cc) Status,
+    _transmit: *const fn (*const ManagedNetworkProtocol, *const ManagedNetworkCompletionToken) callconv(cc) Status,
+    _receive: *const fn (*const ManagedNetworkProtocol, *const ManagedNetworkCompletionToken) callconv(cc) Status,
+    _cancel: *const fn (*const ManagedNetworkProtocol, ?*const ManagedNetworkCompletionToken) callconv(cc) Status,
+    _poll: *const fn (*const ManagedNetworkProtocol) callconv(cc) Status,
 
     /// Returns the operational parameters for the current MNP child driver.
     /// May also support returning the underlying SNP driver mode data.
diff --git a/lib/std/os/uefi/protocols/managed_network_service_binding_protocol.zig b/lib/std/os/uefi/protocols/managed_network_service_binding_protocol.zig
index 79c3add0d00f..ea51a4dcafc7 100644
--- a/lib/std/os/uefi/protocols/managed_network_service_binding_protocol.zig
+++ b/lib/std/os/uefi/protocols/managed_network_service_binding_protocol.zig
@@ -3,10 +3,11 @@ const uefi = std.os.uefi;
 const Handle = uefi.Handle;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const ManagedNetworkServiceBindingProtocol = extern struct {
-    _create_child: *const fn (*const ManagedNetworkServiceBindingProtocol, *?Handle) callconv(.C) Status,
-    _destroy_child: *const fn (*const ManagedNetworkServiceBindingProtocol, Handle) callconv(.C) Status,
+    _create_child: *const fn (*const ManagedNetworkServiceBindingProtocol, *?Handle) callconv(cc) Status,
+    _destroy_child: *const fn (*const ManagedNetworkServiceBindingProtocol, Handle) callconv(cc) Status,
 
     pub fn createChild(self: *const ManagedNetworkServiceBindingProtocol, handle: *?Handle) Status {
         return self._create_child(self, handle);
diff --git a/lib/std/os/uefi/protocols/rng_protocol.zig b/lib/std/os/uefi/protocols/rng_protocol.zig
index 20e32353a79c..19399a0a845b 100644
--- a/lib/std/os/uefi/protocols/rng_protocol.zig
+++ b/lib/std/os/uefi/protocols/rng_protocol.zig
@@ -2,11 +2,12 @@ const std = @import("std");
 const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Random Number Generator protocol
 pub const RNGProtocol = extern struct {
-    _get_info: *const fn (*const RNGProtocol, *usize, [*]align(8) Guid) callconv(.C) Status,
-    _get_rng: *const fn (*const RNGProtocol, ?*align(8) const Guid, usize, [*]u8) callconv(.C) Status,
+    _get_info: *const fn (*const RNGProtocol, *usize, [*]align(8) Guid) callconv(cc) Status,
+    _get_rng: *const fn (*const RNGProtocol, ?*align(8) const Guid, usize, [*]u8) callconv(cc) Status,
 
     /// Returns information about the random number generation implementation.
     pub fn getInfo(self: *const RNGProtocol, list_size: *usize, list: [*]align(8) Guid) Status {
diff --git a/lib/std/os/uefi/protocols/simple_file_system_protocol.zig b/lib/std/os/uefi/protocols/simple_file_system_protocol.zig
index cce24069f6f8..9f73031f6ec3 100644
--- a/lib/std/os/uefi/protocols/simple_file_system_protocol.zig
+++ b/lib/std/os/uefi/protocols/simple_file_system_protocol.zig
@@ -3,10 +3,11 @@ const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const FileProtocol = uefi.protocols.FileProtocol;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const SimpleFileSystemProtocol = extern struct {
     revision: u64,
-    _open_volume: *const fn (*const SimpleFileSystemProtocol, **const FileProtocol) callconv(.C) Status,
+    _open_volume: *const fn (*const SimpleFileSystemProtocol, **const FileProtocol) callconv(cc) Status,
 
     pub fn openVolume(self: *const SimpleFileSystemProtocol, root: **const FileProtocol) Status {
         return self._open_volume(self, root);
diff --git a/lib/std/os/uefi/protocols/simple_network_protocol.zig b/lib/std/os/uefi/protocols/simple_network_protocol.zig
index 2a38267ff8bc..0e6c82b3291b 100644
--- a/lib/std/os/uefi/protocols/simple_network_protocol.zig
+++ b/lib/std/os/uefi/protocols/simple_network_protocol.zig
@@ -3,22 +3,23 @@ const uefi = std.os.uefi;
 const Event = uefi.Event;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const SimpleNetworkProtocol = extern struct {
     revision: u64,
-    _start: *const fn (*const SimpleNetworkProtocol) callconv(.C) Status,
-    _stop: *const fn (*const SimpleNetworkProtocol) callconv(.C) Status,
-    _initialize: *const fn (*const SimpleNetworkProtocol, usize, usize) callconv(.C) Status,
-    _reset: *const fn (*const SimpleNetworkProtocol, bool) callconv(.C) Status,
-    _shutdown: *const fn (*const SimpleNetworkProtocol) callconv(.C) Status,
-    _receive_filters: *const fn (*const SimpleNetworkProtocol, SimpleNetworkReceiveFilter, SimpleNetworkReceiveFilter, bool, usize, ?[*]const MacAddress) callconv(.C) Status,
-    _station_address: *const fn (*const SimpleNetworkProtocol, bool, ?*const MacAddress) callconv(.C) Status,
-    _statistics: *const fn (*const SimpleNetworkProtocol, bool, ?*usize, ?*NetworkStatistics) callconv(.C) Status,
-    _mcast_ip_to_mac: *const fn (*const SimpleNetworkProtocol, bool, *const anyopaque, *MacAddress) callconv(.C) Status,
-    _nvdata: *const fn (*const SimpleNetworkProtocol, bool, usize, usize, [*]u8) callconv(.C) Status,
-    _get_status: *const fn (*const SimpleNetworkProtocol, *SimpleNetworkInterruptStatus, ?*?[*]u8) callconv(.C) Status,
-    _transmit: *const fn (*const SimpleNetworkProtocol, usize, usize, [*]const u8, ?*const MacAddress, ?*const MacAddress, ?*const u16) callconv(.C) Status,
-    _receive: *const fn (*const SimpleNetworkProtocol, ?*usize, *usize, [*]u8, ?*MacAddress, ?*MacAddress, ?*u16) callconv(.C) Status,
+    _start: *const fn (*const SimpleNetworkProtocol) callconv(cc) Status,
+    _stop: *const fn (*const SimpleNetworkProtocol) callconv(cc) Status,
+    _initialize: *const fn (*const SimpleNetworkProtocol, usize, usize) callconv(cc) Status,
+    _reset: *const fn (*const SimpleNetworkProtocol, bool) callconv(cc) Status,
+    _shutdown: *const fn (*const SimpleNetworkProtocol) callconv(cc) Status,
+    _receive_filters: *const fn (*const SimpleNetworkProtocol, SimpleNetworkReceiveFilter, SimpleNetworkReceiveFilter, bool, usize, ?[*]const MacAddress) callconv(cc) Status,
+    _station_address: *const fn (*const SimpleNetworkProtocol, bool, ?*const MacAddress) callconv(cc) Status,
+    _statistics: *const fn (*const SimpleNetworkProtocol, bool, ?*usize, ?*NetworkStatistics) callconv(cc) Status,
+    _mcast_ip_to_mac: *const fn (*const SimpleNetworkProtocol, bool, *const anyopaque, *MacAddress) callconv(cc) Status,
+    _nvdata: *const fn (*const SimpleNetworkProtocol, bool, usize, usize, [*]u8) callconv(cc) Status,
+    _get_status: *const fn (*const SimpleNetworkProtocol, *SimpleNetworkInterruptStatus, ?*?[*]u8) callconv(cc) Status,
+    _transmit: *const fn (*const SimpleNetworkProtocol, usize, usize, [*]const u8, ?*const MacAddress, ?*const MacAddress, ?*const u16) callconv(cc) Status,
+    _receive: *const fn (*const SimpleNetworkProtocol, ?*usize, *usize, [*]u8, ?*MacAddress, ?*MacAddress, ?*u16) callconv(cc) Status,
     wait_for_packet: Event,
     mode: *SimpleNetworkMode,
 
diff --git a/lib/std/os/uefi/protocols/simple_pointer_protocol.zig b/lib/std/os/uefi/protocols/simple_pointer_protocol.zig
index 1f29ba88eb34..8854aece27d0 100644
--- a/lib/std/os/uefi/protocols/simple_pointer_protocol.zig
+++ b/lib/std/os/uefi/protocols/simple_pointer_protocol.zig
@@ -3,11 +3,12 @@ const uefi = std.os.uefi;
 const Event = uefi.Event;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Protocol for mice
 pub const SimplePointerProtocol = struct {
-    _reset: *const fn (*const SimplePointerProtocol, bool) callconv(.C) Status,
-    _get_state: *const fn (*const SimplePointerProtocol, *SimplePointerState) callconv(.C) Status,
+    _reset: *const fn (*const SimplePointerProtocol, bool) callconv(cc) Status,
+    _get_state: *const fn (*const SimplePointerProtocol, *SimplePointerState) callconv(cc) Status,
     wait_for_input: Event,
     mode: *SimplePointerMode,
 
diff --git a/lib/std/os/uefi/protocols/simple_text_input_ex_protocol.zig b/lib/std/os/uefi/protocols/simple_text_input_ex_protocol.zig
index fbcd7338995f..61dd45efa13a 100644
--- a/lib/std/os/uefi/protocols/simple_text_input_ex_protocol.zig
+++ b/lib/std/os/uefi/protocols/simple_text_input_ex_protocol.zig
@@ -3,15 +3,16 @@ const uefi = std.os.uefi;
 const Event = uefi.Event;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Character input devices, e.g. Keyboard
 pub const SimpleTextInputExProtocol = extern struct {
-    _reset: *const fn (*const SimpleTextInputExProtocol, bool) callconv(.C) Status,
-    _read_key_stroke_ex: *const fn (*const SimpleTextInputExProtocol, *KeyData) callconv(.C) Status,
+    _reset: *const fn (*const SimpleTextInputExProtocol, bool) callconv(cc) Status,
+    _read_key_stroke_ex: *const fn (*const SimpleTextInputExProtocol, *KeyData) callconv(cc) Status,
     wait_for_key_ex: Event,
-    _set_state: *const fn (*const SimpleTextInputExProtocol, *const u8) callconv(.C) Status,
-    _register_key_notify: *const fn (*const SimpleTextInputExProtocol, *const KeyData, *const fn (*const KeyData) callconv(.C) usize, **anyopaque) callconv(.C) Status,
-    _unregister_key_notify: *const fn (*const SimpleTextInputExProtocol, *const anyopaque) callconv(.C) Status,
+    _set_state: *const fn (*const SimpleTextInputExProtocol, *const u8) callconv(cc) Status,
+    _register_key_notify: *const fn (*const SimpleTextInputExProtocol, *const KeyData, *const fn (*const KeyData) callconv(cc) usize, **anyopaque) callconv(cc) Status,
+    _unregister_key_notify: *const fn (*const SimpleTextInputExProtocol, *const anyopaque) callconv(cc) Status,
 
     /// Resets the input device hardware.
     pub fn reset(self: *const SimpleTextInputExProtocol, verify: bool) Status {
@@ -29,7 +30,7 @@ pub const SimpleTextInputExProtocol = extern struct {
     }
 
     /// Register a notification function for a particular keystroke for the input device.
-    pub fn registerKeyNotify(self: *const SimpleTextInputExProtocol, key_data: *const KeyData, notify: *const fn (*const KeyData) callconv(.C) usize, handle: **anyopaque) Status {
+    pub fn registerKeyNotify(self: *const SimpleTextInputExProtocol, key_data: *const KeyData, notify: *const fn (*const KeyData) callconv(cc) usize, handle: **anyopaque) Status {
         return self._register_key_notify(self, key_data, notify, handle);
     }
 
diff --git a/lib/std/os/uefi/protocols/simple_text_input_protocol.zig b/lib/std/os/uefi/protocols/simple_text_input_protocol.zig
index 72c33c48a997..7a9f3f1ed8cf 100644
--- a/lib/std/os/uefi/protocols/simple_text_input_protocol.zig
+++ b/lib/std/os/uefi/protocols/simple_text_input_protocol.zig
@@ -4,11 +4,12 @@ const Event = uefi.Event;
 const Guid = uefi.Guid;
 const InputKey = uefi.protocols.InputKey;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Character input devices, e.g. Keyboard
 pub const SimpleTextInputProtocol = extern struct {
-    _reset: *const fn (*const SimpleTextInputProtocol, bool) callconv(.C) Status,
-    _read_key_stroke: *const fn (*const SimpleTextInputProtocol, *InputKey) callconv(.C) Status,
+    _reset: *const fn (*const SimpleTextInputProtocol, bool) callconv(cc) Status,
+    _read_key_stroke: *const fn (*const SimpleTextInputProtocol, *InputKey) callconv(cc) Status,
     wait_for_key: Event,
 
     /// Resets the input device hardware.
diff --git a/lib/std/os/uefi/protocols/simple_text_output_protocol.zig b/lib/std/os/uefi/protocols/simple_text_output_protocol.zig
index 47eb9a6741c2..4281c421c621 100644
--- a/lib/std/os/uefi/protocols/simple_text_output_protocol.zig
+++ b/lib/std/os/uefi/protocols/simple_text_output_protocol.zig
@@ -2,18 +2,19 @@ const std = @import("std");
 const uefi = std.os.uefi;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 /// Character output devices
 pub const SimpleTextOutputProtocol = extern struct {
-    _reset: *const fn (*const SimpleTextOutputProtocol, bool) callconv(.C) Status,
-    _output_string: *const fn (*const SimpleTextOutputProtocol, [*:0]const u16) callconv(.C) Status,
-    _test_string: *const fn (*const SimpleTextOutputProtocol, [*:0]const u16) callconv(.C) Status,
-    _query_mode: *const fn (*const SimpleTextOutputProtocol, usize, *usize, *usize) callconv(.C) Status,
-    _set_mode: *const fn (*const SimpleTextOutputProtocol, usize) callconv(.C) Status,
-    _set_attribute: *const fn (*const SimpleTextOutputProtocol, usize) callconv(.C) Status,
-    _clear_screen: *const fn (*const SimpleTextOutputProtocol) callconv(.C) Status,
-    _set_cursor_position: *const fn (*const SimpleTextOutputProtocol, usize, usize) callconv(.C) Status,
-    _enable_cursor: *const fn (*const SimpleTextOutputProtocol, bool) callconv(.C) Status,
+    _reset: *const fn (*const SimpleTextOutputProtocol, bool) callconv(cc) Status,
+    _output_string: *const fn (*const SimpleTextOutputProtocol, [*:0]const u16) callconv(cc) Status,
+    _test_string: *const fn (*const SimpleTextOutputProtocol, [*:0]const u16) callconv(cc) Status,
+    _query_mode: *const fn (*const SimpleTextOutputProtocol, usize, *usize, *usize) callconv(cc) Status,
+    _set_mode: *const fn (*const SimpleTextOutputProtocol, usize) callconv(cc) Status,
+    _set_attribute: *const fn (*const SimpleTextOutputProtocol, usize) callconv(cc) Status,
+    _clear_screen: *const fn (*const SimpleTextOutputProtocol) callconv(cc) Status,
+    _set_cursor_position: *const fn (*const SimpleTextOutputProtocol, usize, usize) callconv(cc) Status,
+    _enable_cursor: *const fn (*const SimpleTextOutputProtocol, bool) callconv(cc) Status,
     mode: *SimpleTextOutputMode,
 
     /// Resets the text output device hardware.
diff --git a/lib/std/os/uefi/protocols/udp6_protocol.zig b/lib/std/os/uefi/protocols/udp6_protocol.zig
index f772d38d5258..a629836fd7df 100644
--- a/lib/std/os/uefi/protocols/udp6_protocol.zig
+++ b/lib/std/os/uefi/protocols/udp6_protocol.zig
@@ -8,15 +8,16 @@ const Ip6ModeData = uefi.protocols.Ip6ModeData;
 const Ip6Address = uefi.protocols.Ip6Address;
 const ManagedNetworkConfigData = uefi.protocols.ManagedNetworkConfigData;
 const SimpleNetworkMode = uefi.protocols.SimpleNetworkMode;
+const cc = uefi.cc;
 
 pub const Udp6Protocol = extern struct {
-    _get_mode_data: *const fn (*const Udp6Protocol, ?*Udp6ConfigData, ?*Ip6ModeData, ?*ManagedNetworkConfigData, ?*SimpleNetworkMode) callconv(.C) Status,
-    _configure: *const fn (*const Udp6Protocol, ?*const Udp6ConfigData) callconv(.C) Status,
-    _groups: *const fn (*const Udp6Protocol, bool, ?*const Ip6Address) callconv(.C) Status,
-    _transmit: *const fn (*const Udp6Protocol, *Udp6CompletionToken) callconv(.C) Status,
-    _receive: *const fn (*const Udp6Protocol, *Udp6CompletionToken) callconv(.C) Status,
-    _cancel: *const fn (*const Udp6Protocol, ?*Udp6CompletionToken) callconv(.C) Status,
-    _poll: *const fn (*const Udp6Protocol) callconv(.C) Status,
+    _get_mode_data: *const fn (*const Udp6Protocol, ?*Udp6ConfigData, ?*Ip6ModeData, ?*ManagedNetworkConfigData, ?*SimpleNetworkMode) callconv(cc) Status,
+    _configure: *const fn (*const Udp6Protocol, ?*const Udp6ConfigData) callconv(cc) Status,
+    _groups: *const fn (*const Udp6Protocol, bool, ?*const Ip6Address) callconv(cc) Status,
+    _transmit: *const fn (*const Udp6Protocol, *Udp6CompletionToken) callconv(cc) Status,
+    _receive: *const fn (*const Udp6Protocol, *Udp6CompletionToken) callconv(cc) Status,
+    _cancel: *const fn (*const Udp6Protocol, ?*Udp6CompletionToken) callconv(cc) Status,
+    _poll: *const fn (*const Udp6Protocol) callconv(cc) Status,
 
     pub fn getModeData(self: *const Udp6Protocol, udp6_config_data: ?*Udp6ConfigData, ip6_mode_data: ?*Ip6ModeData, mnp_config_data: ?*ManagedNetworkConfigData, snp_mode_data: ?*SimpleNetworkMode) Status {
         return self._get_mode_data(self, udp6_config_data, ip6_mode_data, mnp_config_data, snp_mode_data);
diff --git a/lib/std/os/uefi/protocols/udp6_service_binding_protocol.zig b/lib/std/os/uefi/protocols/udp6_service_binding_protocol.zig
index 9886ecca19fd..8eb74877cbaa 100644
--- a/lib/std/os/uefi/protocols/udp6_service_binding_protocol.zig
+++ b/lib/std/os/uefi/protocols/udp6_service_binding_protocol.zig
@@ -3,10 +3,11 @@ const uefi = std.os.uefi;
 const Handle = uefi.Handle;
 const Guid = uefi.Guid;
 const Status = uefi.Status;
+const cc = uefi.cc;
 
 pub const Udp6ServiceBindingProtocol = extern struct {
-    _create_child: *const fn (*const Udp6ServiceBindingProtocol, *?Handle) callconv(.C) Status,
-    _destroy_child: *const fn (*const Udp6ServiceBindingProtocol, Handle) callconv(.C) Status,
+    _create_child: *const fn (*const Udp6ServiceBindingProtocol, *?Handle) callconv(cc) Status,
+    _destroy_child: *const fn (*const Udp6ServiceBindingProtocol, Handle) callconv(cc) Status,
 
     pub fn createChild(self: *const Udp6ServiceBindingProtocol, handle: *?Handle) Status {
         return self._create_child(self, handle);
diff --git a/lib/std/os/uefi/tables/boot_services.zig b/lib/std/os/uefi/tables/boot_services.zig
index 7fc32decb9e6..e502e3680738 100644
--- a/lib/std/os/uefi/tables/boot_services.zig
+++ b/lib/std/os/uefi/tables/boot_services.zig
@@ -6,6 +6,7 @@ const Handle = uefi.Handle;
 const Status = uefi.Status;
 const TableHeader = uefi.tables.TableHeader;
 const DevicePathProtocol = uefi.protocols.DevicePathProtocol;
+const cc = uefi.cc;
 
 /// Boot services are services provided by the system's firmware until the operating system takes
 /// over control over the hardware by calling exitBootServices.
@@ -22,138 +23,140 @@ pub const BootServices = extern struct {
     hdr: TableHeader,
 
     /// Raises a task's priority level and returns its previous level.
-    raiseTpl: *const fn (new_tpl: usize) callconv(.C) usize,
+    raiseTpl: *const fn (new_tpl: usize) callconv(cc) usize,
 
     /// Restores a task's priority level to its previous value.
-    restoreTpl: *const fn (old_tpl: usize) callconv(.C) void,
+    restoreTpl: *const fn (old_tpl: usize) callconv(cc) void,
 
     /// Allocates memory pages from the system.
-    allocatePages: *const fn (alloc_type: AllocateType, mem_type: MemoryType, pages: usize, memory: *[*]align(4096) u8) callconv(.C) Status,
+    allocatePages: *const fn (alloc_type: AllocateType, mem_type: MemoryType, pages: usize, memory: *[*]align(4096) u8) callconv(cc) Status,
 
     /// Frees memory pages.
-    freePages: *const fn (memory: [*]align(4096) u8, pages: usize) callconv(.C) Status,
+    freePages: *const fn (memory: [*]align(4096) u8, pages: usize) callconv(cc) Status,
 
     /// Returns the current memory map.
-    getMemoryMap: *const fn (mmap_size: *usize, mmap: ?[*]MemoryDescriptor, mapKey: *usize, descriptor_size: *usize, descriptor_version: *u32) callconv(.C) Status,
+    getMemoryMap: *const fn (mmap_size: *usize, mmap: ?[*]MemoryDescriptor, mapKey: *usize, descriptor_size: *usize, descriptor_version: *u32) callconv(cc) Status,
 
     /// Allocates pool memory.
-    allocatePool: *const fn (pool_type: MemoryType, size: usize, buffer: *[*]align(8) u8) callconv(.C) Status,
+    allocatePool: *const fn (pool_type: MemoryType, size: usize, buffer: *[*]align(8) u8) callconv(cc) Status,
 
     /// Returns pool memory to the system.
-    freePool: *const fn (buffer: [*]align(8) u8) callconv(.C) Status,
+    freePool: *const fn (buffer: [*]align(8) u8) callconv(cc) Status,
 
     /// Creates an event.
-    createEvent: *const fn (type: u32, notify_tpl: usize, notify_func: ?*const fn (Event, ?*anyopaque) callconv(.C) void, notifyCtx: ?*const anyopaque, event: *Event) callconv(.C) Status,
+    createEvent: *const fn (type: u32, notify_tpl: usize, notify_func: ?*const fn (Event, ?*anyopaque) callconv(cc) void, notifyCtx: ?*const anyopaque, event: *Event) callconv(cc) Status,
 
     /// Sets the type of timer and the trigger time for a timer event.
-    setTimer: *const fn (event: Event, type: TimerDelay, triggerTime: u64) callconv(.C) Status,
+    setTimer: *const fn (event: Event, type: TimerDelay, triggerTime: u64) callconv(cc) Status,
 
     /// Stops execution until an event is signaled.
-    waitForEvent: *const fn (event_len: usize, events: [*]const Event, index: *usize) callconv(.C) Status,
+    waitForEvent: *const fn (event_len: usize, events: [*]const Event, index: *usize) callconv(cc) Status,
 
     /// Signals an event.
-    signalEvent: *const fn (event: Event) callconv(.C) Status,
+    signalEvent: *const fn (event: Event) callconv(cc) Status,
 
     /// Closes an event.
-    closeEvent: *const fn (event: Event) callconv(.C) Status,
+    closeEvent: *const fn (event: Event) callconv(cc) Status,
 
     /// Checks whether an event is in the signaled state.
-    checkEvent: *const fn (event: Event) callconv(.C) Status,
+    checkEvent: *const fn (event: Event) callconv(cc) Status,
 
     /// Installs a protocol interface on a device handle. If the handle does not exist, it is created
     /// and added to the list of handles in the system. installMultipleProtocolInterfaces()
     /// performs more error checking than installProtocolInterface(), so its use is recommended over this.
-    installProtocolInterface: *const fn (handle: Handle, protocol: *align(8) const Guid, interface_type: EfiInterfaceType, interface: *anyopaque) callconv(.C) Status,
+    installProtocolInterface: *const fn (handle: Handle, protocol: *align(8) const Guid, interface_type: EfiInterfaceType, interface: *anyopaque) callconv(cc) Status,
 
     /// Reinstalls a protocol interface on a device handle
-    reinstallProtocolInterface: *const fn (handle: Handle, protocol: *align(8) const Guid, old_interface: *anyopaque, new_interface: *anyopaque) callconv(.C) Status,
+    reinstallProtocolInterface: *const fn (handle: Handle, protocol: *align(8) const Guid, old_interface: *anyopaque, new_interface: *anyopaque) callconv(cc) Status,
 
     /// Removes a protocol interface from a device handle. Usage of
     /// uninstallMultipleProtocolInterfaces is recommended over this.
-    uninstallProtocolInterface: *const fn (handle: Handle, protocol: *align(8) const Guid, interface: *anyopaque) callconv(.C) Status,
+    uninstallProtocolInterface: *const fn (handle: Handle, protocol: *align(8) const Guid, interface: *anyopaque) callconv(cc) Status,
 
     /// Queries a handle to determine if it supports a specified protocol.
-    handleProtocol: *const fn (handle: Handle, protocol: *align(8) const Guid, interface: *?*anyopaque) callconv(.C) Status,
+    handleProtocol: *const fn (handle: Handle, protocol: *align(8) const Guid, interface: *?*anyopaque) callconv(cc) Status,
 
     reserved: *anyopaque,
 
     /// Creates an event that is to be signaled whenever an interface is installed for a specified protocol.
-    registerProtocolNotify: *const fn (protocol: *align(8) const Guid, event: Event, registration: **anyopaque) callconv(.C) Status,
+    registerProtocolNotify: *const fn (protocol: *align(8) const Guid, event: Event, registration: **anyopaque) callconv(cc) Status,
 
     /// Returns an array of handles that support a specified protocol.
-    locateHandle: *const fn (search_type: LocateSearchType, protocol: ?*align(8) const Guid, search_key: ?*const anyopaque, bufferSize: *usize, buffer: [*]Handle) callconv(.C) Status,
+    locateHandle: *const fn (search_type: LocateSearchType, protocol: ?*align(8) const Guid, search_key: ?*const anyopaque, bufferSize: *usize, buffer: [*]Handle) callconv(cc) Status,
 
     /// Locates the handle to a device on the device path that supports the specified protocol
-    locateDevicePath: *const fn (protocols: *align(8) const Guid, device_path: **const DevicePathProtocol, device: *?Handle) callconv(.C) Status,
+    locateDevicePath: *const fn (protocols: *align(8) const Guid, device_path: **const DevicePathProtocol, device: *?Handle) callconv(cc) Status,
 
     /// Adds, updates, or removes a configuration table entry from the EFI System Table.
-    installConfigurationTable: *const fn (guid: *align(8) const Guid, table: ?*anyopaque) callconv(.C) Status,
+    installConfigurationTable: *const fn (guid: *align(8) const Guid, table: ?*anyopaque) callconv(cc) Status,
 
     /// Loads an EFI image into memory.
-    loadImage: *const fn (boot_policy: bool, parent_image_handle: Handle, device_path: ?*const DevicePathProtocol, source_buffer: ?[*]const u8, source_size: usize, imageHandle: *?Handle) callconv(.C) Status,
+    loadImage: *const fn (boot_policy: bool, parent_image_handle: Handle, device_path: ?*const DevicePathProtocol, source_buffer: ?[*]const u8, source_size: usize, imageHandle: *?Handle) callconv(cc) Status,
 
     /// Transfers control to a loaded image's entry point.
-    startImage: *const fn (image_handle: Handle, exit_data_size: ?*usize, exit_data: ?*[*]u16) callconv(.C) Status,
+    startImage: *const fn (image_handle: Handle, exit_data_size: ?*usize, exit_data: ?*[*]u16) callconv(cc) Status,
 
     /// Terminates a loaded EFI image and returns control to boot services.
-    exit: *const fn (image_handle: Handle, exit_status: Status, exit_data_size: usize, exit_data: ?*const anyopaque) callconv(.C) Status,
+    exit: *const fn (image_handle: Handle, exit_status: Status, exit_data_size: usize, exit_data: ?*const anyopaque) callconv(cc) Status,
 
     /// Unloads an image.
-    unloadImage: *const fn (image_handle: Handle) callconv(.C) Status,
+    unloadImage: *const fn (image_handle: Handle) callconv(cc) Status,
 
     /// Terminates all boot services.
-    exitBootServices: *const fn (image_handle: Handle, map_key: usize) callconv(.C) Status,
+    exitBootServices: *const fn (image_handle: Handle, map_key: usize) callconv(cc) Status,
 
     /// Returns a monotonically increasing count for the platform.
-    getNextMonotonicCount: *const fn (count: *u64) callconv(.C) Status,
+    getNextMonotonicCount: *const fn (count: *u64) callconv(cc) Status,
 
     /// Induces a fine-grained stall.
-    stall: *const fn (microseconds: usize) callconv(.C) Status,
+    stall: *const fn (microseconds: usize) callconv(cc) Status,
 
     /// Sets the system's watchdog timer.
-    setWatchdogTimer: *const fn (timeout: usize, watchdogCode: u64, data_size: usize, watchdog_data: ?[*]const u16) callconv(.C) Status,
+    setWatchdogTimer: *const fn (timeout: usize, watchdogCode: u64, data_size: usize, watchdog_data: ?[*]const u16) callconv(cc) Status,
 
     /// Connects one or more drives to a controller.
-    connectController: *const fn (controller_handle: Handle, driver_image_handle: ?Handle, remaining_device_path: ?*DevicePathProtocol, recursive: bool) callconv(.C) Status,
+    connectController: *const fn (controller_handle: Handle, driver_image_handle: ?Handle, remaining_device_path: ?*DevicePathProtocol, recursive: bool) callconv(cc) Status,
 
     // Disconnects one or more drivers from a controller
-    disconnectController: *const fn (controller_handle: Handle, driver_image_handle: ?Handle, child_handle: ?Handle) callconv(.C) Status,
+    disconnectController: *const fn (controller_handle: Handle, driver_image_handle: ?Handle, child_handle: ?Handle) callconv(cc) Status,
 
     /// Queries a handle to determine if it supports a specified protocol.
-    openProtocol: *const fn (handle: Handle, protocol: *align(8) const Guid, interface: *?*anyopaque, agent_handle: ?Handle, controller_handle: ?Handle, attributes: OpenProtocolAttributes) callconv(.C) Status,
+    openProtocol: *const fn (handle: Handle, protocol: *align(8) const Guid, interface: *?*anyopaque, agent_handle: ?Handle, controller_handle: ?Handle, attributes: OpenProtocolAttributes) callconv(cc) Status,
 
     /// Closes a protocol on a handle that was opened using openProtocol().
-    closeProtocol: *const fn (handle: Handle, protocol: *align(8) const Guid, agentHandle: Handle, controller_handle: ?Handle) callconv(.C) Status,
+    closeProtocol: *const fn (handle: Handle, protocol: *align(8) const Guid, agentHandle: Handle, controller_handle: ?Handle) callconv(cc) Status,
 
     /// Retrieves the list of agents that currently have a protocol interface opened.
-    openProtocolInformation: *const fn (handle: Handle, protocol: *align(8) const Guid, entry_buffer: *[*]ProtocolInformationEntry, entry_count: *usize) callconv(.C) Status,
+    openProtocolInformation: *const fn (handle: Handle, protocol: *align(8) const Guid, entry_buffer: *[*]ProtocolInformationEntry, entry_count: *usize) callconv(cc) Status,
 
     /// Retrieves the list of protocol interface GUIDs that are installed on a handle in a buffer allocated from pool.
-    protocolsPerHandle: *const fn (handle: Handle, protocol_buffer: *[*]*align(8) const Guid, protocol_buffer_count: *usize) callconv(.C) Status,
+    protocolsPerHandle: *const fn (handle: Handle, protocol_buffer: *[*]*align(8) const Guid, protocol_buffer_count: *usize) callconv(cc) Status,
 
     /// Returns an array of handles that support the requested protocol in a buffer allocated from pool.
-    locateHandleBuffer: *const fn (search_type: LocateSearchType, protocol: ?*align(8) const Guid, search_key: ?*const anyopaque, num_handles: *usize, buffer: *[*]Handle) callconv(.C) Status,
+    locateHandleBuffer: *const fn (search_type: LocateSearchType, protocol: ?*align(8) const Guid, search_key: ?*const anyopaque, num_handles: *usize, buffer: *[*]Handle) callconv(cc) Status,
 
     /// Returns the first protocol instance that matches the given protocol.
-    locateProtocol: *const fn (protocol: *align(8) const Guid, registration: ?*const anyopaque, interface: *?*anyopaque) callconv(.C) Status,
+    locateProtocol: *const fn (protocol: *align(8) const Guid, registration: ?*const anyopaque, interface: *?*anyopaque) callconv(cc) Status,
 
     /// Installs one or more protocol interfaces into the boot services environment
+    // TODO: use callconv(cc) instead once that works
     installMultipleProtocolInterfaces: *const fn (handle: *Handle, ...) callconv(.C) Status,
 
     /// Removes one or more protocol interfaces into the boot services environment
+    // TODO: use callconv(cc) instead once that works
     uninstallMultipleProtocolInterfaces: *const fn (handle: *Handle, ...) callconv(.C) Status,
 
     /// Computes and returns a 32-bit CRC for a data buffer.
-    calculateCrc32: *const fn (data: [*]const u8, data_size: usize, *u32) callconv(.C) Status,
+    calculateCrc32: *const fn (data: [*]const u8, data_size: usize, *u32) callconv(cc) Status,
 
     /// Copies the contents of one buffer to another buffer
-    copyMem: *const fn (dest: [*]u8, src: [*]const u8, len: usize) callconv(.C) void,
+    copyMem: *const fn (dest: [*]u8, src: [*]const u8, len: usize) callconv(cc) void,
 
     /// Fills a buffer with a specified value
-    setMem: *const fn (buffer: [*]u8, size: usize, value: u8) callconv(.C) void,
+    setMem: *const fn (buffer: [*]u8, size: usize, value: u8) callconv(cc) void,
 
     /// Creates an event in a group.
-    createEventEx: *const fn (type: u32, notify_tpl: usize, notify_func: EfiEventNotify, notify_ctx: *const anyopaque, event_group: *align(8) const Guid, event: *Event) callconv(.C) Status,
+    createEventEx: *const fn (type: u32, notify_tpl: usize, notify_func: EfiEventNotify, notify_ctx: *const anyopaque, event_group: *align(8) const Guid, event: *Event) callconv(cc) Status,
 
     /// Opens a protocol with a structure as the loaded image for a UEFI application
     pub fn openProtocolSt(self: *BootServices, comptime protocol: type, handle: Handle) !*protocol {
@@ -191,7 +194,7 @@ pub const BootServices = extern struct {
     pub const tpl_high_level: usize = 31;
 };
 
-pub const EfiEventNotify = *const fn (event: Event, ctx: *anyopaque) callconv(.C) void;
+pub const EfiEventNotify = *const fn (event: Event, ctx: *anyopaque) callconv(cc) void;
 
 pub const TimerDelay = enum(u32) {
     TimerCancel,
diff --git a/lib/std/os/uefi/tables/runtime_services.zig b/lib/std/os/uefi/tables/runtime_services.zig
index da155e378e97..d3dc3cb0f488 100644
--- a/lib/std/os/uefi/tables/runtime_services.zig
+++ b/lib/std/os/uefi/tables/runtime_services.zig
@@ -6,6 +6,7 @@ const Time = uefi.Time;
 const TimeCapabilities = uefi.TimeCapabilities;
 const Status = uefi.Status;
 const MemoryDescriptor = uefi.tables.MemoryDescriptor;
+const cc = uefi.cc;
 
 /// Runtime services are provided by the firmware before and after exitBootServices has been called.
 ///
@@ -19,50 +20,50 @@ pub const RuntimeServices = extern struct {
     hdr: TableHeader,
 
     /// Returns the current time and date information, and the time-keeping capabilities of the hardware platform.
-    getTime: *const fn (time: *uefi.Time, capabilities: ?*TimeCapabilities) callconv(.C) Status,
+    getTime: *const fn (time: *uefi.Time, capabilities: ?*TimeCapabilities) callconv(cc) Status,
 
     /// Sets the current local time and date information
-    setTime: *const fn (time: *uefi.Time) callconv(.C) Status,
+    setTime: *const fn (time: *uefi.Time) callconv(cc) Status,
 
     /// Returns the current wakeup alarm clock setting
-    getWakeupTime: *const fn (enabled: *bool, pending: *bool, time: *uefi.Time) callconv(.C) Status,
+    getWakeupTime: *const fn (enabled: *bool, pending: *bool, time: *uefi.Time) callconv(cc) Status,
 
     /// Sets the system wakeup alarm clock time
-    setWakeupTime: *const fn (enable: *bool, time: ?*uefi.Time) callconv(.C) Status,
+    setWakeupTime: *const fn (enable: *bool, time: ?*uefi.Time) callconv(cc) Status,
 
     /// Changes the runtime addressing mode of EFI firmware from physical to virtual.
-    setVirtualAddressMap: *const fn (mmap_size: usize, descriptor_size: usize, descriptor_version: u32, virtual_map: [*]MemoryDescriptor) callconv(.C) Status,
+    setVirtualAddressMap: *const fn (mmap_size: usize, descriptor_size: usize, descriptor_version: u32, virtual_map: [*]MemoryDescriptor) callconv(cc) Status,
 
     /// Determines the new virtual address that is to be used on subsequent memory accesses.
-    convertPointer: *const fn (debug_disposition: usize, address: **anyopaque) callconv(.C) Status,
+    convertPointer: *const fn (debug_disposition: usize, address: **anyopaque) callconv(cc) Status,
 
     /// Returns the value of a variable.
-    getVariable: *const fn (var_name: [*:0]const u16, vendor_guid: *align(8) const Guid, attributes: ?*u32, data_size: *usize, data: ?*anyopaque) callconv(.C) Status,
+    getVariable: *const fn (var_name: [*:0]const u16, vendor_guid: *align(8) const Guid, attributes: ?*u32, data_size: *usize, data: ?*anyopaque) callconv(cc) Status,
 
     /// Enumerates the current variable names.
-    getNextVariableName: *const fn (var_name_size: *usize, var_name: [*:0]u16, vendor_guid: *align(8) Guid) callconv(.C) Status,
+    getNextVariableName: *const fn (var_name_size: *usize, var_name: [*:0]u16, vendor_guid: *align(8) Guid) callconv(cc) Status,
 
     /// Sets the value of a variable.
-    setVariable: *const fn (var_name: [*:0]const u16, vendor_guid: *align(8) const Guid, attributes: u32, data_size: usize, data: *anyopaque) callconv(.C) Status,
+    setVariable: *const fn (var_name: [*:0]const u16, vendor_guid: *align(8) const Guid, attributes: u32, data_size: usize, data: *anyopaque) callconv(cc) Status,
 
     /// Return the next high 32 bits of the platform's monotonic counter
-    getNextHighMonotonicCount: *const fn (high_count: *u32) callconv(.C) Status,
+    getNextHighMonotonicCount: *const fn (high_count: *u32) callconv(cc) Status,
 
     /// Resets the entire platform.
-    resetSystem: *const fn (reset_type: ResetType, reset_status: Status, data_size: usize, reset_data: ?*const anyopaque) callconv(.C) noreturn,
+    resetSystem: *const fn (reset_type: ResetType, reset_status: Status, data_size: usize, reset_data: ?*const anyopaque) callconv(cc) noreturn,
 
     /// Passes capsules to the firmware with both virtual and physical mapping.
     /// Depending on the intended consumption, the firmware may process the capsule immediately.
     /// If the payload should persist across a system reset, the reset value returned from
     /// `queryCapsuleCapabilities` must be passed into resetSystem and will cause the capsule
     /// to be processed by the firmware as part of the reset process.
-    updateCapsule: *const fn (capsule_header_array: **CapsuleHeader, capsule_count: usize, scatter_gather_list: EfiPhysicalAddress) callconv(.C) Status,
+    updateCapsule: *const fn (capsule_header_array: **CapsuleHeader, capsule_count: usize, scatter_gather_list: EfiPhysicalAddress) callconv(cc) Status,
 
     /// Returns if the capsule can be supported via `updateCapsule`
-    queryCapsuleCapabilities: *const fn (capsule_header_array: **CapsuleHeader, capsule_count: usize, maximum_capsule_size: *usize, resetType: ResetType) callconv(.C) Status,
+    queryCapsuleCapabilities: *const fn (capsule_header_array: **CapsuleHeader, capsule_count: usize, maximum_capsule_size: *usize, resetType: ResetType) callconv(cc) Status,
 
     /// Returns information about the EFI variables
-    queryVariableInfo: *const fn (attributes: *u32, maximum_variable_storage_size: *u64, remaining_variable_storage_size: *u64, maximum_variable_size: *u64) callconv(.C) Status,
+    queryVariableInfo: *const fn (attributes: *u32, maximum_variable_storage_size: *u64, remaining_variable_storage_size: *u64, maximum_variable_size: *u64) callconv(cc) Status,
 
     pub const signature: u64 = 0x56524553544e5552;
 };
diff --git a/src/Sema.zig b/src/Sema.zig
index bfefcef8e2b9..0066f1ad8792 100644
--- a/src/Sema.zig
+++ b/src/Sema.zig
@@ -6628,7 +6628,7 @@ fn checkCallArgumentCount(
     const fn_params_len = func_ty_info.param_types.len;
     const args_len = total_args - @intFromBool(member_fn);
     if (func_ty_info.is_var_args) {
-        assert(func_ty_info.cc == .C);
+        assert(callConvSupportsVarArgs(func_ty_info.cc));
         if (total_args >= fn_params_len) return func_ty;
     } else if (fn_params_len == total_args) {
         return func_ty;
@@ -8917,6 +8917,41 @@ fn handleExternLibName(
     return sema.gpa.dupeZ(u8, lib_name);
 }
 
+/// These are calling conventions that are confirmed to work with variadic functions.
+/// Any calling conventions not included here are either not yet verified to work with variadic
+/// functions or there are no more other calling conventions that support variadic functions.
+const calling_conventions_supporting_var_args = [_]std.builtin.CallingConvention{
+    .C,
+};
+fn callConvSupportsVarArgs(cc: std.builtin.CallingConvention) bool {
+    return for (calling_conventions_supporting_var_args) |supported_cc| {
+        if (cc == supported_cc) return true;
+    } else false;
+}
+fn checkCallConvSupportsVarArgs(sema: *Sema, block: *Block, src: LazySrcLoc, cc: std.builtin.CallingConvention) CompileError!void {
+    const CallingConventionsSupportingVarArgsList = struct {
+        pub fn format(_: @This(), comptime fmt: []const u8, options: std.fmt.FormatOptions, writer: anytype) !void {
+            _ = fmt;
+            _ = options;
+            for (calling_conventions_supporting_var_args, 0..) |cc_inner, i| {
+                if (i != 0)
+                    try writer.writeAll(", ");
+                try writer.print("'.{s}'", .{@tagName(cc_inner)});
+            }
+        }
+    };
+
+    if (!callConvSupportsVarArgs(cc)) {
+        const msg = msg: {
+            const msg = try sema.errMsg(block, src, "variadic function does not support '.{s}' calling convention", .{@tagName(cc)});
+            errdefer msg.destroy(sema.gpa);
+            try sema.errNote(block, src, msg, "supported calling conventions: {}", .{CallingConventionsSupportingVarArgsList{}});
+            break :msg msg;
+        };
+        return sema.failWithOwnedErrorMsg(msg);
+    }
+}
+
 const FuncLinkSection = union(enum) {
     generic,
     default,
@@ -8963,9 +8998,7 @@ fn funcCommon(
         if (is_generic) {
             return sema.fail(block, func_src, "generic function cannot be variadic", .{});
         }
-        if (cc.? != .C) {
-            return sema.fail(block, cc_src, "variadic function must have 'C' calling convention", .{});
-        }
+        try sema.checkCallConvSupportsVarArgs(block, cc_src, cc.?);
     }
 
     var destroy_fn_on_error = false;
@@ -20325,8 +20358,8 @@ fn zirReify(
 
             const is_var_args = is_var_args_val.toBool();
             const cc = mod.toEnum(std.builtin.CallingConvention, calling_convention_val);
-            if (is_var_args and cc != .C) {
-                return sema.fail(block, src, "varargs functions must have C calling convention", .{});
+            if (is_var_args) {
+                try sema.checkCallConvSupportsVarArgs(block, src, cc);
             }
 
             const alignment = alignment: {
diff --git a/test/cases/compile_errors/invalid_variadic_function.zig b/test/cases/compile_errors/invalid_variadic_function.zig
index 7652cb329a08..d0b6d2c8f5e9 100644
--- a/test/cases/compile_errors/invalid_variadic_function.zig
+++ b/test/cases/compile_errors/invalid_variadic_function.zig
@@ -1,5 +1,6 @@
 fn foo(...) void {}
 fn bar(a: anytype, ...) callconv(a) void {}
+inline fn foo2(...) void {}
 
 comptime {
     _ = foo;
@@ -7,10 +8,16 @@ comptime {
 comptime {
     _ = bar;
 }
+comptime {
+    _ = foo2;
+}
 
 // error
 // backend=stage2
 // target=native
 //
-// :1:1: error: variadic function must have 'C' calling convention
+// :1:1: error: variadic function does not support '.Unspecified' calling convention
+// :1:1: note: supported calling conventions: '.C'
 // :2:1: error: generic function cannot be variadic
+// :1:1: error: variadic function does not support '.Inline' calling convention
+// :1:1: note: supported calling conventions: '.C'
diff --git a/test/cases/compile_errors/reify_type.Fn_with_is_var_args_true_and_non-C_callconv.zig b/test/cases/compile_errors/reify_type.Fn_with_is_var_args_true_and_non-C_callconv.zig
index a341435b36ba..678fbe3ed7be 100644
--- a/test/cases/compile_errors/reify_type.Fn_with_is_var_args_true_and_non-C_callconv.zig
+++ b/test/cases/compile_errors/reify_type.Fn_with_is_var_args_true_and_non-C_callconv.zig
@@ -16,4 +16,5 @@ comptime {
 // backend=stage2
 // target=native
 //
-// :1:13: error: varargs functions must have C calling convention
+// :1:13: error: variadic function does not support '.Unspecified' calling convention
+// :1:13: note: supported calling conventions: '.C'