feat(asm): emit the amd64 stack-split guard and morestack block

asm/link.go

@@ -91,6 +91,8 @@ type RelocKind int
 
 const (
 	RelPCRel32         RelocKind = iota // 32-bit PC-relative (amd64)
+	RelCall                             // R_CALL: CALL to a function symbol (amd64)
+	RelTLSLE                            // R_TLS_LE: local-exec TLS load, no symbol (amd64 guard)
 	RelRISCVPCRELIType                  // R_RISCV_PCREL_ITYPE (AUIPC + I-type pair)
 	RelRISCVPCRELSType                  // R_RISCV_PCREL_STYPE (AUIPC + S-type pair)
 	RelRISCVJal                         // R_RISCV_JAL (J-type call)
@@ -148,6 +150,7 @@ func AssembleFile(f *ast.File) (*Image, error) {
 	link := &linkInfo{symbols: known, allowExternal: true}
 
 	img := &Image{Symbols: map[string]int{}}
+	textOff := map[string]int{}
 	type asmFunc struct {
 		name    string
 		patches []sbPatch
@@ -185,6 +188,7 @@ func AssembleFile(f *ast.File) (*Image, error) {
 		for _, s := range steps {
 			fl.Spadj = append(fl.Spadj, SpadjStep{PC: s.pc, Value: s.value})
 		}
+		textOff[t.Name.Name] = len(img.Code)
 		img.Funcs = append(img.Funcs, fl)
 		img.Code = append(img.Code, code...)
 		funcs = append(funcs, asmFunc{name: t.Name.Name, patches: patches})
@@ -217,13 +221,27 @@ func AssembleFile(f *ast.File) (*Image, error) {
 		base := img.Funcs[i].Offset
 		code := img.Code[base : base+img.Funcs[i].Size]
 		for _, p := range fn.patches {
-			reloc := Reloc{Off: p.off, After: p.after, Name: p.name, Addend: p.addend}
+			reloc := Reloc{Off: p.off, After: p.after, Name: p.name, Addend: p.addend, Kind: p.kind}
+			if p.kind == RelTLSLE {
+				// The TLS slot has no symbol: the linker fills the offset
+				// from the runtime's TLS layout.
+				img.Funcs[i].Relocs = append(img.Funcs[i].Relocs, reloc)
+				continue
+			}
 			if imgOff, ok := img.Symbols[p.name]; ok {
 				rel := int64(imgOff) + p.addend - int64(base+p.after)
 				if rel < -1<<31 || rel >= 1<<31 {
 					return nil, fmt.Errorf("%s: displacement to %q out of rel32 range", fn.name, p.name)
 				}
 				copy(code[p.off:p.off+4], le32(rel))
+			} else if imgOff, ok := textOff[p.name]; ok {
+				// A CALL to a TEXT function of the same file: resolve the
+				// displacement against the function's layout position.
+				rel := int64(imgOff) + p.addend - int64(base+p.after)
+				if rel < -1<<31 || rel >= 1<<31 {
+					return nil, fmt.Errorf("%s: displacement to %q out of rel32 range", fn.name, p.name)
+				}
+				copy(code[p.off:p.off+4], le32(rel))
 			} else {
 				reloc.External = true
 				externals[p.name] = true