Revert "cmd/link: fix GC data reading from shared library"

This reverts CL 240462.

Reason for revert: test fails on PPC64LE.

Updates #39927.

Change-Id: I4f14fd0c36e604a80ae9f2f86d1e643e28945e93
Reviewed-on: https://go-review.googlesource.com/c/go/+/240616
Reviewed-by: Austin Clements <[email protected]>
Reviewed-by: Than McIntosh <[email protected]>

Author: cherrymui

misc/cgo/testshared/shared_test.go

@@ -38,15 +38,7 @@ var testWork = flag.Bool("testwork", false, "if true, log and do not delete the
 
 // run runs a command and calls t.Errorf if it fails.
 func run(t *testing.T, msg string, args ...string) {
-	runWithEnv(t, msg, nil, args...)
-}
-
-// runWithEnv runs a command under the given environment and calls t.Errorf if it fails.
-func runWithEnv(t *testing.T, msg string, env []string, args ...string) {
 	c := exec.Command(args[0], args[1:]...)
-	if len(env) != 0 {
-		c.Env = append(os.Environ(), env...)
-	}
 	if output, err := c.CombinedOutput(); err != nil {
 		t.Errorf("executing %s (%s) failed %s:\n%s", strings.Join(args, " "), msg, err, output)
 	}
@@ -1042,11 +1034,3 @@ func TestGeneratedHash(t *testing.T) {
 func TestPackageOrder(t *testing.T) {
 	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./issue39777/a", "./issue39777/b")
 }
-
-// Test that GC data are generated correctly by the linker when it needs a type defined in
-// a shared library. See issue 39927.
-func TestGCData(t *testing.T) {
-	goCmd(t, "install", "-buildmode=shared", "-linkshared", "./gcdata/p")
-	goCmd(t, "build", "-linkshared", "./gcdata/main")
-	runWithEnv(t, "running gcdata/main", []string{"GODEBUG=clobberfree=1"}, "./main")
-}

misc/cgo/testshared/testdata/gcdata/main/main.go

@@ -10,7 +10,6 @@ import (
 	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
 	"debug/elf"
-	"log"
 )
 
 // Decoding the type.* symbols.	 This has to be in sync with
@@ -230,15 +229,8 @@ func decodetypeGcmask(ctxt *Link, s loader.Sym) []byte {
 		ptrdata := decodetypePtrdata(ctxt.Arch, symData)
 		sect := findShlibSection(ctxt, ctxt.loader.SymPkg(s), addr)
 		if sect != nil {
-			bits := ptrdata / int64(ctxt.Arch.PtrSize)
-			r := make([]byte, (bits+7)/8)
-			// ldshlibsyms avoids closing the ELF file so sect.ReadAt works.
-			// If we remove this read (and the ones in decodetypeGcprog), we
-			// can close the file.
-			_, err := sect.ReadAt(r, int64(addr-sect.Addr))
-			if err != nil {
-				log.Fatal(err)
-			}
+			r := make([]byte, ptrdata/int64(ctxt.Arch.PtrSize))
+			sect.ReadAt(r, int64(addr-sect.Addr))
 			return r
 		}
 		Exitf("cannot find gcmask for %s", ctxt.loader.SymName(s))
@@ -259,15 +251,9 @@ func decodetypeGcprog(ctxt *Link, s loader.Sym) []byte {
 			// A gcprog is a 4-byte uint32 indicating length, followed by
 			// the actual program.
 			progsize := make([]byte, 4)
-			_, err := sect.ReadAt(progsize, int64(addr-sect.Addr))
-			if err != nil {
-				log.Fatal(err)
-			}
+			sect.ReadAt(progsize, int64(addr-sect.Addr))
 			progbytes := make([]byte, ctxt.Arch.ByteOrder.Uint32(progsize))
-			_, err = sect.ReadAt(progbytes, int64(addr-sect.Addr+4))
-			if err != nil {
-				log.Fatal(err)
-			}
+			sect.ReadAt(progbytes, int64(addr-sect.Addr+4))
 			return append(progsize, progbytes...)
 		}
 		Exitf("cannot find gcmask for %s", ctxt.loader.SymName(s))
@@ -282,7 +268,7 @@ func decodetypeGcprog(ctxt *Link, s loader.Sym) []byte {
 func findShlibSection(ctxt *Link, path string, addr uint64) *elf.Section {
 	for _, shlib := range ctxt.Shlibs {
 		if shlib.Path == path {
-			for _, sect := range shlib.File.Sections[1:] { // skip the NULL section
+			for _, sect := range shlib.File.Sections {
 				if sect.Addr <= addr && addr <= sect.Addr+sect.Size {
 					return sect
 				}
@@ -293,5 +279,8 @@ func findShlibSection(ctxt *Link, path string, addr uint64) *elf.Section {
 }
 
 func decodetypeGcprogShlib(ctxt *Link, data []byte) uint64 {
+	if ctxt.Arch.Family == sys.ARM64 {
+		return 0
+	}
 	return decodeInuxi(ctxt.Arch, data[2*int32(ctxt.Arch.PtrSize)+8+1*int32(ctxt.Arch.PtrSize):], ctxt.Arch.PtrSize)
 }

misc/cgo/testshared/testdata/gcdata/p/p.go

@@ -2124,9 +2124,7 @@ func ldshlibsyms(ctxt *Link, shlib string) {
 		Errorf(nil, "cannot open shared library: %s", libpath)
 		return
 	}
-	// Keep the file open as decodetypeGcprog needs to read from it.
-	// TODO: fix. Maybe mmap the file.
-	//defer f.Close()
+	defer f.Close()
 
 	hash, err := readnote(f, ELF_NOTE_GO_NAME, ELF_NOTE_GOABIHASH_TAG)
 	if err != nil {