feat(asm): the TLS access pair in the toolchain's one-instruction form

Assisted-by: GLM 5.3 Flash

asm/link.go

@@ -150,6 +150,18 @@ func (img *Image) Bytes() []byte {
 	return append(out, img.Data...)
 }
 
+// AssembleOption adjusts the file-level assembly context.
+type AssembleOption func(*linkInfo)
+
+// WithGOOS selects the target operating system for the forms that depend on
+// it, the TLS access shape above all: linux and freebsd take the
+// one-instruction form, windows and plan9 keep the two-instruction load.
+func WithGOOS(goos string) AssembleOption {
+	return func(l *linkInfo) {
+		l.goos = goos
+	}
+}
+
 // AssembleFile assembles every TEXT function of a parsed file and lays out
 // its static symbols (GLOBL/DATA) in a data section behind the code.  Each
 // reference to a file-local static symbol becomes a RIP-relative load whose
@@ -157,7 +169,7 @@ func (img *Image) Bytes() []byte {
 // GLOBL defines is recorded as an external relocation (Externals) with its
 // displacement left zero, the object-file emitters resolve it at link
 // time, while the raw image (Bytes) cannot represent it.
-func AssembleFile(f *ast.File) (*Image, error) {
+func AssembleFile(f *ast.File, opts ...AssembleOption) (*Image, error) {
 	dataSyms, err := collectData(f)
 	if err != nil {
 		return nil, err
@@ -174,6 +186,9 @@ func AssembleFile(f *ast.File) (*Image, error) {
 		}
 	}
 	link := &linkInfo{symbols: known, allowExternal: true}
+	for _, o := range opts {
+		o(link)
+	}
 	poolSeen := map[string]bool{}
 
 	img := &Image{Symbols: map[string]int{}, SourcePath: f.Path}