feat(asm): the operand forms and defines GOROOT writes

Assisted-by: GLM 5.3 Flash

parser/parser.go

@@ -489,6 +489,17 @@ func parseImmediate(g []token.Token) ast.Immediate {
 	} else if g[i].Kind == token.Plus {
 		i++
 	}
+	// A constant expression after the sign: $-(R - 8), $+(32-shift).  The
+	// toolchain folds the negated value in place (the cgo ABI macros write
+	// ADJSP $-(REGS_HOST_TO_ABI0_STACK - 8)), so the sign applies to the
+	// folded value exactly as it does to a bare literal.
+	if i < len(g) && (g[i].Kind == token.LParen || g[i].Kind == token.Tilde) {
+		if v, rest, ok := foldExpr(g[i:]); ok && len(rest) == 0 {
+			imm.Val = v
+			imm.HasVal = true
+			return imm
+		}
+	}
 	if i < len(g) && g[i].Kind == token.Number {
 		text := g[i].Text
 		if v, ok := tryInt(text); ok {

parser/preproc.go

@@ -34,6 +34,12 @@ type Options struct {
 	// Expand enables macro expansion, include splicing and the
 	// statement-separator reading of ';' that the expanded bodies rely on.
 	Expand bool
+	// Predefines names the macros defined before the file is read.  The
+	// go command drives go tool asm with -D GOOS_<goos> -D GOARCH_<arch>,
+	// and GOROOT's own headers (go_tls.h, asm_riscv64.h) select their
+	// platform blocks with #ifdef on exactly those names, so an assembler
+	// without them cannot see the platform definitions at all.
+	Predefines map[string]string
 }
 
 // ParseWithOptions parses src like Parse, optionally preprocessing it first.
@@ -44,6 +50,9 @@ func ParseWithOptions(path, src string, opts Options) (*ast.File, []error) {
 	var errs []error
 	if opts.Expand {
 		pp := &preproc{opts: opts, macros: map[string]*macroDef{}}
+		for name, value := range opts.Predefines {
+			pp.macros[name] = &macroDef{name: name, body: lexer.Tokenize(value)}
+		}
 		lines = pp.fileLines(path, tokens, token.Position{})
 		errs = pp.errs
 	} else {