From 4f74de1e4d8ac8382d866d9918059144218da069 Mon Sep 17 00:00:00 2001 From: Shawn Walker-Salas Date: Wed, 26 Aug 2015 15:24:41 -0700 Subject: [PATCH] cmd/go: fix Go buildid reading on Solaris MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit TestNoteReading fails on Solaris with linkmode=external due to some assumptions made about how ELF .note sections are written by some linkers. On current versions of Solaris and older derivatives, SHF_ALLOC is intentionally ignored for .note sections unless the .note section is assigned to the text segment via a mapfile. Also, if .note sections are assigned to the text segment, no PT_NOTE program header will be created thwarting Go's attempts at attempting to quickly find the .note. Furthermore, Go assumes that the relevant note segment will be placed early in the file while the Solaris linker currently places the note segment last in the file, additionally thwarting Go's optimisation attempts that read only the first 16KB of the file to find the buildid. The fix is to detect when the note section is outside of the first 16KB of the file and then fallback to additionally reading that section of the file. This way, in future versions of Solaris when this linking behaviour is changed, the fast path will always succeed and we'll only be slower if it fails; likewise, any other linker that does this will also just work. Fixes #12178 Change-Id: I61c1dc3f744ae3ad63938386d2ace8a432c0efe1 Reviewed-on: https://go-review.googlesource.com/14210 Run-TryBot: Aram Hăvărneanu Reviewed-by: Aram Hăvărneanu --- src/cmd/go/note.go | 32 ++++++++++++++++++++++++++------ src/cmd/go/note_test.go | 3 --- src/cmd/link/internal/ld/elf.go | 4 ---- 3 files changed, 26 insertions(+), 13 deletions(-) diff --git a/src/cmd/go/note.go b/src/cmd/go/note.go index 97e18651e4a..5c953c4d004 100644 --- a/src/cmd/go/note.go +++ b/src/cmd/go/note.go @@ -69,11 +69,11 @@ func readELFNote(filename, name string, typ int32) ([]byte, error) { var elfGoNote = []byte("Go\x00\x00") -// readELFGoBuildID the Go build ID string from an ELF binary. -// The Go build ID is stored in a note described by an ELF PT_NOTE prog header. -// The caller has already opened filename, to get f, and read the first 4 kB out, in data. +// The Go build ID is stored in a note described by an ELF PT_NOTE prog +// header. The caller has already opened filename, to get f, and read +// at least 4 kB out, in data. func readELFGoBuildID(filename string, f *os.File, data []byte) (buildid string, err error) { - // Assume the note content is in the first 4 kB, already read. + // Assume the note content is in the data, already read. // Rewrite the ELF header to set shnum to 0, so that we can pass // the data to elf.NewFile and it will decode the Prog list but not // try to read the section headers and the string table from disk. @@ -95,11 +95,31 @@ func readELFGoBuildID(filename string, f *os.File, data []byte) (buildid string, return "", &os.PathError{Path: filename, Op: "parse", Err: err} } for _, p := range ef.Progs { - if p.Type != elf.PT_NOTE || p.Off >= uint64(len(data)) || p.Off+p.Filesz >= uint64(len(data)) || p.Filesz < 16 { + if p.Type != elf.PT_NOTE || p.Filesz < 16 { continue } - note := data[p.Off : p.Off+p.Filesz] + var note []byte + if p.Off+p.Filesz < uint64(len(data)) { + note = data[p.Off : p.Off+p.Filesz] + } else { + // For some linkers, such as the Solaris linker, + // the buildid may not be found in data (which + // likely contains the first 16kB of the file) + // or even the first few megabytes of the file + // due to differences in note segment placement; + // in that case, extract the note data manually. + _, err = f.Seek(int64(p.Off), 0) + if err != nil { + return "", err + } + + note = make([]byte, p.Filesz) + _, err = io.ReadFull(f, note) + if err != nil { + return "", err + } + } nameSize := ef.ByteOrder.Uint32(note) valSize := ef.ByteOrder.Uint32(note[4:]) tag := ef.ByteOrder.Uint32(note[8:]) diff --git a/src/cmd/go/note_test.go b/src/cmd/go/note_test.go index 2fcfe34d67e..0764b73312e 100644 --- a/src/cmd/go/note_test.go +++ b/src/cmd/go/note_test.go @@ -33,9 +33,6 @@ func TestNoteReading(t *testing.T) { // no external linking t.Logf("no external linking - skipping linkmode=external test") - case "solaris": - t.Logf("skipping - golang.org/issue/12178") - default: tg.run("build", "-ldflags", "-buildid="+buildID+" -linkmode=external", "-o", tg.path("hello.exe"), tg.path("hello.go")) id, err := main.ReadBuildIDFromBinary(tg.path("hello.exe")) diff --git a/src/cmd/link/internal/ld/elf.go b/src/cmd/link/internal/ld/elf.go index 187643e41b7..baca0326a5b 100644 --- a/src/cmd/link/internal/ld/elf.go +++ b/src/cmd/link/internal/ld/elf.go @@ -1725,10 +1725,6 @@ func doelf() { Addstring(shstrtab, ".note.go.pkg-list") Addstring(shstrtab, ".note.go.deps") } - - if buildid != "" { - Addstring(shstrtab, ".note.go.buildid") - } } hasinitarr := Linkshared