Introduce umode binary and map it in salus user space address.

Cargo.toml

@@ -34,9 +34,12 @@ s_mode_utils = { path = "./s-mode-utils" }
 sbi = { path = "./sbi" }
 spin = { version = "*", default-features = false }
 sha2 = {version = "0.10", default-features = false }
+riscv_elf = { path = "./riscv-elf" }
 
 [workspace]
 
 members = [
+	"libuser",
+	"umode",
         "test-workloads",
 ]

Makefile

@@ -65,21 +65,23 @@ check:
 		--target $(HOST_TRIPLET) \
 		--workspace \
 		--exclude test_workloads \
+		--exclude libuser \
 		--lib
 	cargo test \
 		--target $(HOST_TRIPLET) \
 		--workspace \
 		--exclude test_workloads \
+		--exclude libuser \
 		--doc
 
 CARGO_FLAGS :=
 
 .PHONY: salus
-salus:
+salus: umode
 	cargo build $(CARGO_FLAGS) --release --bin salus
 
 .PHONY: salus_debug
-salus_debug:
+salus_debug: umode
 	cargo build $(CARGO_FLAGS) --bin salus
 
 tellus_bin: tellus
@@ -94,6 +96,10 @@ guestvm:
 tellus: guestvm
 	cargo build $(CARGO_FLAGS) --package test_workloads --bin tellus --release
 
+.PHONY: umode
+umode:
+	RUSTFLAGS='-Clink-arg=-Tlds/umode.lds' cargo build  --release --package umode
+
 # Runnable targets:
 #
 #  run_tellus_gdb: Run Tellus as the host VM with GDB debugging enabled.

lds/umode.lds

@@ -0,0 +1,47 @@
+OUTPUT_ARCH( "riscv" )
+
+ENTRY( _start )
+
+PHDRS
+{
+    text PT_LOAD;
+    rodata PT_LOAD;
+    data PT_LOAD;
+    stack PT_LOAD;
+}
+
+SECTIONS
+{
+    . = 0xffffffff00000000;
+
+    .text ALIGN(4096) : {
+        *(.text.start)
+        *(.text.init) *(.text .text.*)
+    } :text
+
+    .rodata ALIGN(4096) : {
+        *(.rodata .rodata.*)
+    } :rodata
+
+    .data ALIGN(4096) : {
+        *(.data .data.*)
+
+        . = ALIGN(8);
+        PROVIDE(__global_pointer$ = .);
+        *(.sdata .sdata.*)
+
+        *(.sbss .sbss.*) *(.bss .bss.*)
+    } :data
+
+    . += 4096;
+
+    .stack ALIGN(4096) (NOLOAD) : {
+    PROVIDE(_stack_start = .);
+    . += 4096;
+    PROVIDE(_stack_end = .);
+    } :stack
+
+    /DISCARD/ : {
+        *(.eh_frame)
+    }
+}

libuser/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "libuser"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

libuser/src/lib.rs

@@ -0,0 +1,21 @@
+// Copyright (c) 2022 by Rivos Inc.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+#![no_std]
+
+use core::arch::{asm, global_asm};
+
+global_asm!(include_str!("task_start.S"));
+
+// Loop making ecalls as the kernel will kill the task on an ecall (the only syscall supported is
+// `exit`).
+#[panic_handler]
+fn panic(_info: &core::panic::PanicInfo) -> ! {
+    // Safe to make an ecall that won't return.
+    unsafe {
+        loop {
+            asm!("ecall");
+        }
+    }
+}

libuser/src/task_start.S

@@ -0,0 +1,23 @@
+// Copyright (c) 2021 by Rivos Inc.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+.option norvc
+
+.section .text.start
+
+// The entry point for a task.
+.global _start
+_start:
+
+.option push
+.option norelax
+    la gp, __global_pointer$
+.option pop
+    la sp, _stack_end
+
+    call task_main
+
+    // ecall to exit
+    ecall
+

riscv-elf/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "riscv_elf"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+[dependencies]
+arrayvec = { version = "0.7.2", default-features = false }