From: Cherry Zhang Date: Thu, 3 Sep 2020 16:59:09 +0000 (-0400) Subject: cmd/link: put read-only data in __DATA_CONST segment X-Git-Tag: go1.16beta1~1079 X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=ffd95aadcddc34ec2c83971346f04cf7234e0fca;p=gostls13.git cmd/link: put read-only data in __DATA_CONST segment On darwin, we put read-only data in __TEXT segment on AMD64 in exe (non-PIE) buildmode, and in __DATA on everywhere else. This is not ideal: things in __DATA segment are not read-only, and being mapped R/W may use more run-time resources. In fact, newer darwin systems support a __DATA_CONST segment, which the dynamic linker will map it read-only after applying relocations. Use that. Fixes #38830. Change-Id: Ic281e6c6ca8ef5fec4bb7c5b71c50dd5393e78ae Reviewed-on: https://go-review.googlesource.com/c/go/+/253919 Reviewed-by: Than McIntosh --- diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go index 8324a98a26..a730125cf2 100644 --- a/src/cmd/link/internal/ld/data.go +++ b/src/cmd/link/internal/ld/data.go @@ -930,7 +930,7 @@ func writeBlock(ctxt *Link, out *OutBuf, ldr *loader.Loader, syms []loader.Sym, break } if val < addr { - ldr.Errorf(s, "phase error: addr=%#x but sym=%#x type=%d", addr, val, ldr.SymType(s)) + ldr.Errorf(s, "phase error: addr=%#x but sym=%#x type=%v sect=%v", addr, val, ldr.SymType(s), ldr.SymSect(s).Name) errorexit() } if addr < val { @@ -1308,9 +1308,9 @@ func (state *dodataState) makeRelroForSharedLib(target *Link) { // relro Type before it reaches here. isRelro = true case sym.SFUNCTAB: - if target.IsAIX() && ldr.SymName(s) == "runtime.etypes" { + if ldr.SymName(s) == "runtime.etypes" { // runtime.etypes must be at the end of - // the relro datas. + // the relro data. isRelro = true } } @@ -1706,7 +1706,7 @@ func (state *dodataState) allocateDataSections(ctxt *Link) { ldr.SetSymSect(ldr.LookupOrCreateSym("runtime.ebss", 0), sect) bssGcEnd := state.datsize - int64(sect.Vaddr) - // Emit gcdata for bcc symbols now that symbol values have been assigned. + // Emit gcdata for bss symbols now that symbol values have been assigned. gcsToEmit := []struct { symName string symKind sym.SymKind @@ -1826,13 +1826,16 @@ func (state *dodataState) allocateDataSections(ctxt *Link) { const fallbackPerm = 04 relroSecPerm := fallbackPerm genrelrosecname := func(suffix string) string { + if suffix == "" { + return ".rodata" + } return suffix } seg := segro if ctxt.UseRelro() { segrelro := &Segrelrodata - if ctxt.LinkMode == LinkExternal && ctxt.HeadType != objabi.Haix { + if ctxt.LinkMode == LinkExternal && !ctxt.IsAIX() && !ctxt.IsDarwin() { // Using a separate segment with an external // linker results in some programs moving // their data sections unexpectedly, which @@ -1845,9 +1848,12 @@ func (state *dodataState) allocateDataSections(ctxt *Link) { state.datsize = 0 } - genrelrosecname = func(suffix string) string { - return ".data.rel.ro" + suffix + if !ctxt.IsDarwin() { // We don't need the special names on darwin. + genrelrosecname = func(suffix string) string { + return ".data.rel.ro" + suffix + } } + relroReadOnly := []sym.SymKind{} for _, symnro := range sym.ReadOnly { symn := sym.RelROMap[symnro] diff --git a/src/cmd/link/internal/ld/macho.go b/src/cmd/link/internal/ld/macho.go index f6356729a6..9765ce18d3 100644 --- a/src/cmd/link/internal/ld/macho.go +++ b/src/cmd/link/internal/ld/macho.go @@ -499,16 +499,7 @@ func machoadddynlib(lib string, linkmode LinkMode) { func machoshbits(ctxt *Link, mseg *MachoSeg, sect *sym.Section, segname string) { buf := "__" + strings.Replace(sect.Name[1:], ".", "_", -1) - var msect *MachoSect - if sect.Rwx&1 == 0 && segname != "__DWARF" && (ctxt.Arch.Family == sys.ARM64 || - (ctxt.Arch.Family == sys.AMD64 && ctxt.BuildMode != BuildModeExe)) { - // Darwin external linker on arm64, and on amd64 in c-shared/c-archive buildmode - // complains about absolute relocs in __TEXT, so if the section is not - // executable, put it in __DATA segment. - msect = newMachoSect(mseg, buf, "__DATA") - } else { - msect = newMachoSect(mseg, buf, segname) - } + msect := newMachoSect(mseg, buf, segname) if sect.Rellen > 0 { msect.reloc = uint32(sect.Reloff) @@ -633,13 +624,28 @@ func asmbMacho(ctxt *Link) { machoshbits(ctxt, ms, sect, "__TEXT") } + /* rodata */ + if ctxt.LinkMode != LinkExternal && Segrelrodata.Length > 0 { + ms = newMachoSeg("__DATA_CONST", 20) + ms.vaddr = Segrelrodata.Vaddr + ms.vsize = Segrelrodata.Length + ms.fileoffset = Segrelrodata.Fileoff + ms.filesize = Segrelrodata.Filelen + ms.prot1 = 3 + ms.prot2 = 3 + ms.flag = 0x10 // SG_READ_ONLY + } + + for _, sect := range Segrelrodata.Sections { + machoshbits(ctxt, ms, sect, "__DATA_CONST") + } + /* data */ if ctxt.LinkMode != LinkExternal { - w := int64(Segdata.Length) ms = newMachoSeg("__DATA", 20) - ms.vaddr = uint64(va) + uint64(v) - ms.vsize = uint64(w) - ms.fileoffset = uint64(v) + ms.vaddr = Segdata.Vaddr + ms.vsize = Segdata.Length + ms.fileoffset = Segdata.Fileoff ms.filesize = Segdata.Filelen ms.prot1 = 3 ms.prot2 = 3 @@ -695,7 +701,7 @@ func asmbMacho(ctxt *Link) { if ctxt.LinkMode != LinkExternal { ms := newMachoSeg("__LINKEDIT", 0) - ms.vaddr = uint64(va) + uint64(v) + uint64(Rnd(int64(Segdata.Length), int64(*FlagRound))) + ms.vaddr = uint64(Rnd(int64(Segdata.Vaddr+Segdata.Length), int64(*FlagRound))) ms.vsize = uint64(s1) + uint64(s2) + uint64(s3) + uint64(s4) ms.fileoffset = uint64(linkoff) ms.filesize = ms.vsize @@ -1008,7 +1014,7 @@ func doMachoLink(ctxt *Link) int64 { size := int(ldr.SymSize(s1) + ldr.SymSize(s2) + ldr.SymSize(s3) + ldr.SymSize(s4)) if size > 0 { - linkoff = Rnd(int64(uint64(HEADR)+Segtext.Length), int64(*FlagRound)) + Rnd(int64(Segdata.Filelen), int64(*FlagRound)) + Rnd(int64(Segdwarf.Filelen), int64(*FlagRound)) + linkoff = Rnd(int64(uint64(HEADR)+Segtext.Length), int64(*FlagRound)) + Rnd(int64(Segrelrodata.Filelen), int64(*FlagRound)) + Rnd(int64(Segdata.Filelen), int64(*FlagRound)) + Rnd(int64(Segdwarf.Filelen), int64(*FlagRound)) ctxt.Out.SeekSet(linkoff) ctxt.Out.Write(ldr.Data(s1)) @@ -1086,6 +1092,9 @@ func machoEmitReloc(ctxt *Link) { for _, sect := range Segtext.Sections[1:] { relocSect(ctxt, sect, ctxt.datap) } + for _, sect := range Segrelrodata.Sections { + relocSect(ctxt, sect, ctxt.datap) + } for _, sect := range Segdata.Sections { relocSect(ctxt, sect, ctxt.datap) } diff --git a/src/cmd/link/internal/ld/target.go b/src/cmd/link/internal/ld/target.go index 102b6c5436..f68de8fff1 100644 --- a/src/cmd/link/internal/ld/target.go +++ b/src/cmd/link/internal/ld/target.go @@ -74,8 +74,12 @@ func (t *Target) IsDynlinkingGo() bool { func (t *Target) UseRelro() bool { switch t.BuildMode { case BuildModeCArchive, BuildModeCShared, BuildModeShared, BuildModePIE, BuildModePlugin: - return t.IsELF || t.HeadType == objabi.Haix + return t.IsELF || t.HeadType == objabi.Haix || t.HeadType == objabi.Hdarwin default: + if t.HeadType == objabi.Hdarwin && t.IsARM64() { + // On darwin/ARM64, everything is PIE. + return true + } return t.linkShared || (t.HeadType == objabi.Haix && t.LinkMode == LinkExternal) } }