From 7799756a50f0a4070d66c67e9615375f852f2c04 Mon Sep 17 00:00:00 2001 From: Cherry Zhang Date: Mon, 29 Jun 2020 17:07:17 -0400 Subject: [PATCH] cmd/link: fix GC data reading from shared library (attempt 2) When linking against a Go shared library, when a global variable in the main module has a type defined in the shared library, the linker needs to pull the GC data from the shared library to build the GC program for the global variable. Currently, this fails silently, as the shared library file is closed too early and the read failed (with no error check), causing a zero GC map emitted for the variable, which in turn causes the runtime to treat the variable as pointerless. For now, fix this by keeping the file open. In the future we may want to use mmap to read from the shared library instead. Also add error checking. And fix a (mostly harmless) mistake in size caluculation. Also remove an erroneous condition for ARM64. ARM64 used to have a special case to get the addend from the relocation on the gcdata field. That was removed, but the new code accidentally returned 0 unconditionally. It's no longer necessary to have any special case, since the addend is now applied directly to the gcdata field on ARM64, like on all the other platforms. Fixes #39927. This is the second attempt of CL 240462. And this reverts CL 240616. Change-Id: I01c82422b9f67e872d833336885935bc509bc91b Reviewed-on: https://go-review.googlesource.com/c/go/+/240621 Run-TryBot: Cherry Zhang TryBot-Result: Gobot Gobot Reviewed-by: Than McIntosh --- misc/cgo/testshared/shared_test.go | 16 ++++++++ .../testshared/testdata/gcdata/main/main.go | 37 +++++++++++++++++++ misc/cgo/testshared/testdata/gcdata/p/p.go | 7 ++++ src/cmd/link/internal/ld/decodesym.go | 27 ++++++++++---- src/cmd/link/internal/ld/lib.go | 4 +- 5 files changed, 82 insertions(+), 9 deletions(-) create mode 100644 misc/cgo/testshared/testdata/gcdata/main/main.go create mode 100644 misc/cgo/testshared/testdata/gcdata/p/p.go diff --git a/misc/cgo/testshared/shared_test.go b/misc/cgo/testshared/shared_test.go index fda3d2ce76f..f8dabbe7a01 100644 --- a/misc/cgo/testshared/shared_test.go +++ b/misc/cgo/testshared/shared_test.go @@ -38,7 +38,15 @@ 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) } @@ -1034,3 +1042,11 @@ 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") +} diff --git a/misc/cgo/testshared/testdata/gcdata/main/main.go b/misc/cgo/testshared/testdata/gcdata/main/main.go new file mode 100644 index 00000000000..394862fd94c --- /dev/null +++ b/misc/cgo/testshared/testdata/gcdata/main/main.go @@ -0,0 +1,37 @@ +// Copyright 2020 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +// Test that GC data is generated correctly for global +// variables with types defined in a shared library. +// See issue 39927. + +// This test run under GODEBUG=clobberfree=1. The check +// *x[i] == 12345 depends on this debug mode to clobber +// the value if the object is freed prematurely. + +package main + +import ( + "fmt" + "runtime" + "testshared/gcdata/p" +) + +var x p.T + +func main() { + for i := range x { + x[i] = new(int) + *x[i] = 12345 + } + runtime.GC() + runtime.GC() + runtime.GC() + for i := range x { + if *x[i] != 12345 { + fmt.Printf("x[%d] == %d, want 12345\n", i, *x[i]) + panic("FAIL") + } + } +} diff --git a/misc/cgo/testshared/testdata/gcdata/p/p.go b/misc/cgo/testshared/testdata/gcdata/p/p.go new file mode 100644 index 00000000000..1fee75429ef --- /dev/null +++ b/misc/cgo/testshared/testdata/gcdata/p/p.go @@ -0,0 +1,7 @@ +// Copyright 2020 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package p + +type T [10]*int diff --git a/src/cmd/link/internal/ld/decodesym.go b/src/cmd/link/internal/ld/decodesym.go index e9c87efe379..21bcc3a726a 100644 --- a/src/cmd/link/internal/ld/decodesym.go +++ b/src/cmd/link/internal/ld/decodesym.go @@ -10,6 +10,7 @@ import ( "cmd/link/internal/loader" "cmd/link/internal/sym" "debug/elf" + "log" ) // Decoding the type.* symbols. This has to be in sync with @@ -229,8 +230,15 @@ func decodetypeGcmask(ctxt *Link, s loader.Sym) []byte { ptrdata := decodetypePtrdata(ctxt.Arch, symData) sect := findShlibSection(ctxt, ctxt.loader.SymPkg(s), addr) if sect != nil { - r := make([]byte, ptrdata/int64(ctxt.Arch.PtrSize)) - sect.ReadAt(r, int64(addr-sect.Addr)) + 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) + } return r } Exitf("cannot find gcmask for %s", ctxt.loader.SymName(s)) @@ -251,9 +259,15 @@ 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) - sect.ReadAt(progsize, int64(addr-sect.Addr)) + _, err := sect.ReadAt(progsize, int64(addr-sect.Addr)) + if err != nil { + log.Fatal(err) + } progbytes := make([]byte, ctxt.Arch.ByteOrder.Uint32(progsize)) - sect.ReadAt(progbytes, int64(addr-sect.Addr+4)) + _, err = sect.ReadAt(progbytes, int64(addr-sect.Addr+4)) + if err != nil { + log.Fatal(err) + } return append(progsize, progbytes...) } Exitf("cannot find gcmask for %s", ctxt.loader.SymName(s)) @@ -268,7 +282,7 @@ 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 { + for _, sect := range shlib.File.Sections[1:] { // skip the NULL section if sect.Addr <= addr && addr <= sect.Addr+sect.Size { return sect } @@ -279,8 +293,5 @@ 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) } diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go index 7b6fd9594df..b0a9613e4f4 100644 --- a/src/cmd/link/internal/ld/lib.go +++ b/src/cmd/link/internal/ld/lib.go @@ -2126,7 +2126,9 @@ func ldshlibsyms(ctxt *Link, shlib string) { Errorf(nil, "cannot open shared library: %s", libpath) return } - defer f.Close() + // Keep the file open as decodetypeGcprog needs to read from it. + // TODO: fix. Maybe mmap the file. + //defer f.Close() hash, err := readnote(f, ELF_NOTE_GO_NAME, ELF_NOTE_GOABIHASH_TAG) if err != nil {