build: provide vmlinux

Signed-off-by: Leonardo Di Donato <[email protected]>

vmlinux/xmake.lua

@@ -0,0 +1,45 @@
+set_xmakever("2.6.1") -- Minimum version to compile BPF source correctly
+
+-- options
+--- run `xmake f --generate-vmlinux=y` to always generate vmlinux.h rather than assuming one exists in vmlinux/
+option("generate-vmlinux", {showmenu = true, default = false, description = "always generate vmlinux.h"})
+
+-- vmlinux
+local vmlinuxh = path.join("vmlinux", "vmlinux.h")
+target("vmlinux")
+    set_kind("headeronly")
+    add_includedirs(path.join("$(projectdir)", "vmlinux"), { public = true })
+
+    local missing = false
+    if has_config("generate-vmlinux") then
+        -- We're gonna need bpftool to generate the vmlinux.h
+        includes("../tools")
+        add_deps("bpftool")
+    else
+        if not os.exists(path.absolute(vmlinuxh, os.projectdir())) then
+            -- We're assuming you provide a vmlinux.h
+            missing = true
+        end
+    end
+
+    before_build(function(target)
+        -- Ensure vmlinux.h exists
+        if missing then
+            os.raise("missing " .. vmlinuxh .. ": provide it or configure xmake to generate one for you with xmake f --generate-vmlinux=y")
+        end
+
+        import("utils.progress")
+        if has_config("generate-vmlinux") then
+            -- Generate vmlinux.h
+            progress.show(20, "${color.build.object}generating.vmlinux %s", vmlinuxh)
+            local bpftool = path.join("tools", "bpftool")
+            os.execv(bpftool, { "btf", "dump", "file", "/sys/kernel/btf/vmlinux", "format", "c" }, { stdout = vmlinuxh })
+        end
+    end)
+    on_clean(function(target)
+        -- Delete vmlinux.h if we always generate it
+        if has_config("generate-vmlinux") then
+            os.tryrm(vmlinuxh)
+        end
+        -- Otherwise do nothing to keep the vmlinux.h the user provided
+    end)