feat(asm): resolve external GOOBJ symbols from archive data

asm/goobj.go

@@ -213,16 +213,50 @@ func (img *Image) GOObject(pkgPath, srcPath string) ([]byte, error) {
 		})
 	}
 
+	// Resolve external symbol references (cross-package).  Build the
+	// package index table and determine each external symbol's SymIdx
+	// by reading the target package's export data.
+	var extPkgTable []string
+	var extPkgIdx map[string]int
+	var extSymIdx map[string]int
+	if len(img.Externals) > 0 {
+		var err error
+		extPkgTable, extPkgIdx, extSymIdx, err = resolveExternalSymbols(img.Externals)
+		if err != nil {
+			return nil, fmt.Errorf("GOOBJ emission: resolving external symbols: %w", err)
+		}
+	}
+
 	// Relocations, per defined symbol in definition order (package defs,
-	// then non-package defs).  Only file-local GLOBL references resolve;
-	// external symbols need the import machinery of a later increment.
+	// then non-package defs).
 	nsyms := len(defs) + len(nps)
 	symRelocs := make([][]byte, nsyms) // flat 23-byte records
 	for i, fn := range img.Funcs {
 		si := len(defs) + fnNpIdx[i]
 		for _, r := range fn.Relocs {
 			if r.External {
-				return nil, fmt.Errorf("GOOBJ emission: external symbol %q is not supported yet", r.Name)
+				// Split package-qualified name: "runtime·morestack" → runtime, morestack.
+				pkg, name := splitQualified(r.Name)
+				if pkg == "" {
+					return nil, fmt.Errorf("GOOBJ emission: external symbol %q has no package prefix", r.Name)
+				}
+				pIdx, ok := extPkgIdx[pkg]
+				if !ok {
+					return nil, fmt.Errorf("GOOBJ emission: package %q not resolved", pkg)
+				}
+				sIdx, ok := extSymIdx[pkg+"·"+name]
+				if !ok {
+					return nil, fmt.Errorf("GOOBJ emission: symbol %s·%s not resolved", pkg, name)
+				}
+				var rec [23]byte
+				binary.LittleEndian.PutUint32(rec[0:], uint32(int32(r.Off)))
+				rec[4] = 4 // field width
+				binary.LittleEndian.PutUint16(rec[5:], relocPCRel)
+				binary.LittleEndian.PutUint64(rec[7:], uint64(r.Addend))
+				binary.LittleEndian.PutUint32(rec[15:], uint32(pIdx))
+				binary.LittleEndian.PutUint32(rec[19:], uint32(sIdx))
+				symRelocs[si] = append(symRelocs[si], rec[:]...)
+				continue
 			}
 			di, ok := defIdx[r.Name]
 			if !ok {
@@ -291,7 +325,16 @@ func (img *Image) GOObject(pkgPath, srcPath string) ([]byte, error) {
 	for _, s := range nps {
 		npdefBlk = s.sym.append(npdefBlk, strOff)
 	}
-	pkgIdxBlk := stringRef(nil, "") // index 0: the dummy invalid package
+
+	// Package index table: index 0 is the dummy invalid package.
+	// External packages follow, in pkgIdx order.
+	for _, pkg := range extPkgTable {
+		addStr(pkg)
+	}
+	pkgIdxBlk := stringRef(nil, "") // index 0: dummy
+	for _, pkg := range extPkgTable {
+		pkgIdxBlk = stringRef(pkgIdxBlk, pkg)
+	}
 	fileBlk := stringRef(nil, srcPath)
 
 	var relocBlk, auxBlk, dataBlk []byte