UEFI Target Groundwork: Add LinkerFlavor compile option (#5465)

* Add LinkerFlavor so the odd pairing of COFF+Linux is possible (necessary for UEFI)

* But back bits of builder.go that were mistakenly removed

* Update compileopts/config.go

Co-authored-by: Ayke <aykevanlaethem@gmail.com>

* update LinkerFlavor test

---------

Co-authored-by: Ayke <aykevanlaethem@gmail.com>

builder/build.go

@@ -839,22 +839,25 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 			}
 			ldflags = append(ldflags, "-mllvm", "-mcpu="+config.CPU())
 			ldflags = append(ldflags, "-mllvm", "-mattr="+config.Features()) // needed for MIPS softfloat
-			if config.GOOS() == "windows" {
+			switch config.LinkerFlavor() {
-				// Options for the MinGW wrapper for the lld COFF linker.
+			case "coff":
+				// Options for driving ld.lld in PE/COFF mode.
 				ldflags = append(ldflags,
 					"-Xlink=/opt:lldlto="+strconv.Itoa(speedLevel),
 					"--thinlto-cache-dir="+filepath.Join(cacheDir, "thinlto"))
-			} else if config.GOOS() == "darwin" {
+			case "darwin":
 				// Options for the ld64-compatible lld linker.
 				ldflags = append(ldflags,
 					"--lto-O"+strconv.Itoa(speedLevel),
 					"-cache_path_lto", filepath.Join(cacheDir, "thinlto"))
-			} else {
+			case "gnu":
 				// Options for the ELF linker.
 				ldflags = append(ldflags,
 					"--lto-O"+strconv.Itoa(speedLevel),
 					"--thinlto-cache-dir="+filepath.Join(cacheDir, "thinlto"),
 				)
+			default:
+				return fmt.Errorf("unknown linker flavor: %s", config.LinkerFlavor())
 			}
 			if config.CodeModel() != "default" {
 				ldflags = append(ldflags,

compileopts/config.go

@@ -461,6 +461,22 @@ func (c *Config) LDFlags() []string {
 	return ldflags
 }
 
+// LinkerFlavor returns how the configured linker should be driven.
+// Usually this is derived from GOOS, but targets may override it explicitly.
+func (c *Config) LinkerFlavor() string {
+	if c.Target.LinkerFlavor != "" {
+		return c.Target.LinkerFlavor
+	}
+	switch c.GOOS() {
+	case "windows":
+		return "coff"
+	case "darwin":
+		return "darwin"
+	default:
+		return "gnu"
+	}
+}
+
 // ExtraFiles returns the list of extra files to be built and linked with the
 // executable. This can include extra C and assembly files.
 func (c *Config) ExtraFiles() []string {

compileopts/target.go

@@ -38,7 +38,8 @@ type TargetSpec struct {
 	Scheduler        string   `json:"scheduler,omitempty"`
 	Serial           string   `json:"serial,omitempty"` // which serial output to use (uart, usb, none)
 	Linker           string   `json:"linker,omitempty"`
-	RTLib            string   `json:"rtlib,omitempty"` // compiler runtime library (libgcc, compiler-rt)
+	LinkerFlavor     string   `json:"linker-flavor,omitempty"` // how to drive the configured linker (for example: gnu, coff, darwin)
+	RTLib            string   `json:"rtlib,omitempty"`         // compiler runtime library (libgcc, compiler-rt)
 	Libc             string   `json:"libc,omitempty"`
 	AutoStackSize    *bool    `json:"automatic-stack-size,omitempty"` // Determine stack size automatically at compile time.
 	DefaultStackSize uint64   `json:"default-stack-size,omitempty"`   // Default stack size if the size couldn't be determined at compile time.

compileopts/target_test.go

@@ -112,3 +112,52 @@ func TestOverrideProperties(t *testing.T) {
 	}
 
 }
+
+func TestConfigLinkerFlavor(t *testing.T) {
+	tests := []struct {
+		name   string
+		target *TargetSpec
+		goos   string
+		want   string
+	}{
+		{
+			name:   "default gnu",
+			target: &TargetSpec{},
+			goos:   "linux",
+			want:   "gnu",
+		},
+		{
+			name:   "default coff",
+			target: &TargetSpec{},
+			goos:   "windows",
+			want:   "coff",
+		},
+		{
+			name:   "default darwin",
+			target: &TargetSpec{},
+			goos:   "darwin",
+			want:   "darwin",
+		},
+		{
+			name: "target override",
+			target: &TargetSpec{
+				LinkerFlavor: "coff",
+			},
+			goos: "linux",
+			want: "coff",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			tc.target.GOOS = tc.goos
+			config := &Config{
+				Options: &Options{},
+				Target:  tc.target,
+			}
+			if got := config.LinkerFlavor(); got != tc.want {
+				t.Fatalf("LinkerFlavor() = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}