From f46a5b1e4559191363dbd4f510105dd31ae97aaa Mon Sep 17 00:00:00 2001 From: Cherry Zhang Date: Sun, 11 Oct 2020 15:48:22 -0400 Subject: [PATCH] cmd/link: support PIE internal linking on darwin/amd64 This CL adds support of PIE internal linking on darwin/amd64. This is also preparation for supporting internal linking on darwin/arm64 (macOS), which requires PIE for everything. Updates #38485. Change-Id: I2ed58583dcc102f5e0521982491fc7ba6f2754ed Reviewed-on: https://go-review.googlesource.com/c/go/+/261642 Trust: Cherry Zhang Reviewed-by: Than McIntosh --- misc/cgo/test/issue4029.c | 1 + misc/cgo/test/issue4029.go | 4 + misc/cgo/test/issue4029w.go | 2 +- src/cmd/dist/test.go | 17 +- src/cmd/internal/sys/supported.go | 3 +- src/cmd/link/internal/amd64/asm.go | 65 +++-- src/cmd/link/internal/ld/config.go | 1 + src/cmd/link/internal/ld/lib.go | 6 + src/cmd/link/internal/ld/macho.go | 226 +++++++++++++++++- src/cmd/link/internal/loader/symbolbuilder.go | 18 ++ 10 files changed, 289 insertions(+), 54 deletions(-) diff --git a/misc/cgo/test/issue4029.c b/misc/cgo/test/issue4029.c index 30646ade02..e6a777fe64 100644 --- a/misc/cgo/test/issue4029.c +++ b/misc/cgo/test/issue4029.c @@ -3,6 +3,7 @@ // license that can be found in the LICENSE file. // +build !windows,!static +// +build !darwin !internal_pie #include #include diff --git a/misc/cgo/test/issue4029.go b/misc/cgo/test/issue4029.go index 1bf029d760..8602ce19e2 100644 --- a/misc/cgo/test/issue4029.go +++ b/misc/cgo/test/issue4029.go @@ -3,6 +3,10 @@ // license that can be found in the LICENSE file. // +build !windows,!static +// +build !darwin !internal_pie + +// Excluded in darwin internal linking PIE mode, as dynamic export is not +// supported. package cgotest diff --git a/misc/cgo/test/issue4029w.go b/misc/cgo/test/issue4029w.go index eee33f7010..de0cf2138a 100644 --- a/misc/cgo/test/issue4029w.go +++ b/misc/cgo/test/issue4029w.go @@ -2,7 +2,7 @@ // Use of this source code is governed by a BSD-style // license that can be found in the LICENSE file. -// +build windows static +// +build windows static darwin,internal_pie package cgotest diff --git a/src/cmd/dist/test.go b/src/cmd/dist/test.go index 03e6866d62..94b81613a9 100644 --- a/src/cmd/dist/test.go +++ b/src/cmd/dist/test.go @@ -964,10 +964,10 @@ func (t *tester) internalLink() bool { func (t *tester) internalLinkPIE() bool { switch goos + "-" + goarch { - case "linux-amd64", "linux-arm64", - "android-arm64": - return true - case "windows-amd64", "windows-386", "windows-arm": + case "darwin-amd64", + "linux-amd64", "linux-arm64", + "android-arm64", + "windows-amd64", "windows-386", "windows-arm": return true } return false @@ -1100,6 +1100,13 @@ func (t *tester) cgoTest(dt *distTest) error { cmd = t.addCmd(dt, "misc/cgo/test", t.goTest(), "-ldflags", "-linkmode=external -s") + if t.supportedBuildmode("pie") { + t.addCmd(dt, "misc/cgo/test", t.goTest(), "-buildmode=pie") + if t.internalLink() && t.internalLinkPIE() { + t.addCmd(dt, "misc/cgo/test", t.goTest(), "-buildmode=pie", "-ldflags=-linkmode=internal", "-tags=internal,internal_pie") + } + } + case "aix-ppc64", "android-arm", "android-arm64", "dragonfly-amd64", @@ -1151,7 +1158,7 @@ func (t *tester) cgoTest(dt *distTest) error { if t.supportedBuildmode("pie") { t.addCmd(dt, "misc/cgo/test", t.goTest(), "-buildmode=pie") if t.internalLink() && t.internalLinkPIE() { - t.addCmd(dt, "misc/cgo/test", t.goTest(), "-buildmode=pie", "-ldflags=-linkmode=internal") + t.addCmd(dt, "misc/cgo/test", t.goTest(), "-buildmode=pie", "-ldflags=-linkmode=internal", "-tags=internal,internal_pie") } t.addCmd(dt, "misc/cgo/testtls", t.goTest(), "-buildmode=pie") t.addCmd(dt, "misc/cgo/nocgo", t.goTest(), "-buildmode=pie") diff --git a/src/cmd/internal/sys/supported.go b/src/cmd/internal/sys/supported.go index 55709f3915..07be998035 100644 --- a/src/cmd/internal/sys/supported.go +++ b/src/cmd/internal/sys/supported.go @@ -118,7 +118,8 @@ func BuildModeSupported(compiler, buildmode, goos, goarch string) bool { func InternalLinkPIESupported(goos, goarch string) bool { switch goos + "/" + goarch { - case "linux/amd64", "linux/arm64", + case "darwin/amd64", + "linux/amd64", "linux/arm64", "android/arm64", "windows-amd64", "windows-386", "windows-arm": return true diff --git a/src/cmd/link/internal/amd64/asm.go b/src/cmd/link/internal/amd64/asm.go index e5a6ef51b0..3658ac0be0 100644 --- a/src/cmd/link/internal/amd64/asm.go +++ b/src/cmd/link/internal/amd64/asm.go @@ -76,9 +76,9 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade targType = ldr.SymType(targ) } - switch r.Type() { + switch rt := r.Type(); rt { default: - if r.Type() >= objabi.ElfRelocOffset { + if rt >= objabi.ElfRelocOffset { ldr.Errorf(s, "unexpected relocation type %d (%s)", r.Type(), sym.RelocName(target.Arch, r.Type())) return false } @@ -167,13 +167,24 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_UNSIGNED*2 + 0, objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_SIGNED*2 + 0, objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_BRANCH*2 + 0: - // TODO: What is the difference between all these? su := ldr.MakeSymbolUpdater(s) su.SetRelocType(rIdx, objabi.R_ADDR) if targType == sym.SDYNIMPORT { ldr.Errorf(s, "unexpected reloc for dynamic symbol %s", ldr.SymName(targ)) } + if target.IsPIE() && target.IsInternal() { + // For internal linking PIE, this R_ADDR relocation cannot + // be resolved statically. We need to generate a dynamic + // relocation. Let the code below handle it. + if rt == objabi.MachoRelocOffset+ld.MACHO_X86_64_RELOC_UNSIGNED*2 { + break + } else { + // MACHO_X86_64_RELOC_SIGNED or MACHO_X86_64_RELOC_BRANCH + // Can this happen? The object is expected to be PIC. + ldr.Errorf(s, "unsupported relocation for PIE: %v", rt) + } + } return true case objabi.MachoRelocOffset + ld.MACHO_X86_64_RELOC_BRANCH*2 + 1: @@ -223,7 +234,7 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade if targType != sym.SDYNIMPORT { ldr.Errorf(s, "unexpected GOT reloc for non-dynamic symbol %s", ldr.SymName(targ)) } - ld.AddGotSym(target, ldr, syms, targ, uint32(elf.R_X86_64_GLOB_DAT)) + ld.AddGotSym(target, ldr, syms, targ, 0) su := ldr.MakeSymbolUpdater(s) su.SetRelocType(rIdx, objabi.R_PCREL) su.SetRelocSym(rIdx, syms.GOT) @@ -355,28 +366,15 @@ func adddynrel(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade return true } - if target.IsDarwin() && ldr.SymSize(s) == int64(target.Arch.PtrSize) && r.Off() == 0 { + if target.IsDarwin() { // Mach-O relocations are a royal pain to lay out. - // They use a compact stateful bytecode representation - // that is too much bother to deal with. - // Instead, interpret the C declaration - // void *_Cvar_stderr = &stderr; - // as making _Cvar_stderr the name of a GOT entry - // for stderr. This is separate from the usual GOT entry, - // just in case the C code assigns to the variable, - // and of course it only works for single pointers, - // but we only need to support cgo and that's all it needs. - ld.Adddynsym(ldr, target, syms, targ) - - got := ldr.MakeSymbolUpdater(syms.GOT) - su := ldr.MakeSymbolUpdater(s) - su.SetType(got.Type()) - got.AddInteriorSym(s) - su.SetValue(got.Size()) - got.AddUint64(target.Arch, 0) - leg := ldr.MakeSymbolUpdater(syms.LinkEditGOT) - leg.AddUint32(target.Arch, uint32(ldr.SymDynid(targ))) - su.SetRelocType(rIdx, objabi.ElfRelocOffset) // ignore during relocsym + // They use a compact stateful bytecode representation. + // Here we record what are needed and encode them later. + ld.MachoAddRebase(s, int64(r.Off())) + // Not mark r done here. So we still apply it statically, + // so in the file content we'll also have the right offset + // to the relocation target. So it can be examined statically + // (e.g. go version). return true } } @@ -627,26 +625,16 @@ func addpltsym(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade ldr.SetPlt(s, int32(plt.Size()-16)) } else if target.IsDarwin() { - // To do lazy symbol lookup right, we're supposed - // to tell the dynamic loader which library each - // symbol comes from and format the link info - // section just so. I'm too lazy (ha!) to do that - // so for now we'll just use non-lazy pointers, - // which don't need to be told which library to use. - // - // https://networkpx.blogspot.com/2009/09/about-lcdyldinfoonly-command.html - // has details about what we're avoiding. - - ld.AddGotSym(target, ldr, syms, s, uint32(elf.R_X86_64_GLOB_DAT)) - plt := ldr.MakeSymbolUpdater(syms.PLT) + ld.AddGotSym(target, ldr, syms, s, 0) sDynid := ldr.SymDynid(s) lep := ldr.MakeSymbolUpdater(syms.LinkEditPLT) lep.AddUint32(target.Arch, uint32(sDynid)) - // jmpq *got+size(IP) + plt := ldr.MakeSymbolUpdater(syms.PLT) ldr.SetPlt(s, int32(plt.Size())) + // jmpq *got+size(IP) plt.AddUint8(0xff) plt.AddUint8(0x25) plt.AddPCRelPlus(target.Arch, syms.GOT, int64(ldr.SymGot(s))) @@ -654,6 +642,7 @@ func addpltsym(target *ld.Target, ldr *loader.Loader, syms *ld.ArchSyms, s loade ldr.Errorf(s, "addpltsym: unsupported binary format") } } + func tlsIEtoLE(P []byte, off, size int) { // Transform the PC-relative instruction into a constant load. // That is, diff --git a/src/cmd/link/internal/ld/config.go b/src/cmd/link/internal/ld/config.go index aaf74b58de..c680d11c1d 100644 --- a/src/cmd/link/internal/ld/config.go +++ b/src/cmd/link/internal/ld/config.go @@ -222,6 +222,7 @@ func mustLinkExternal(ctxt *Link) (res bool, reason string) { switch objabi.GOOS + "/" + objabi.GOARCH { case "linux/amd64", "linux/arm64", "android/arm64": case "windows/386", "windows/amd64", "windows/arm": + case "darwin/amd64": default: // Internal linking does not support TLS_IE. return true, "buildmode=pie" diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go index 5fe028d321..8d04973fcf 100644 --- a/src/cmd/link/internal/ld/lib.go +++ b/src/cmd/link/internal/ld/lib.go @@ -2526,6 +2526,12 @@ func AddGotSym(target *Target, ldr *loader.Loader, syms *ArchSyms, s loader.Sym, } else if target.IsDarwin() { leg := ldr.MakeSymbolUpdater(syms.LinkEditGOT) leg.AddUint32(target.Arch, uint32(ldr.SymDynid(s))) + if target.IsPIE() && target.IsInternal() { + // Mach-O relocations are a royal pain to lay out. + // They use a compact stateful bytecode representation. + // Here we record what are needed and encode them later. + MachoAddBind(int64(ldr.SymGot(s)), s) + } } else { ldr.Errorf(s, "addgotsym: unsupported binary format") } diff --git a/src/cmd/link/internal/ld/macho.go b/src/cmd/link/internal/ld/macho.go index eab6537c75..a19a4afd9a 100644 --- a/src/cmd/link/internal/ld/macho.go +++ b/src/cmd/link/internal/ld/macho.go @@ -118,6 +118,8 @@ const ( MH_EXECUTE = 0x2 MH_NOUNDEFS = 0x1 + MH_DYLDLINK = 0x4 + MH_PIE = 0x200000 ) const ( @@ -193,6 +195,56 @@ const ( PLATFORM_BRIDGEOS MachoPlatform = 5 ) +// rebase table opcode +const ( + REBASE_TYPE_POINTER = 1 + REBASE_TYPE_TEXT_ABSOLUTE32 = 2 + REBASE_TYPE_TEXT_PCREL32 = 3 + + REBASE_OPCODE_MASK = 0xF0 + REBASE_IMMEDIATE_MASK = 0x0F + REBASE_OPCODE_DONE = 0x00 + REBASE_OPCODE_SET_TYPE_IMM = 0x10 + REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB = 0x20 + REBASE_OPCODE_ADD_ADDR_ULEB = 0x30 + REBASE_OPCODE_ADD_ADDR_IMM_SCALED = 0x40 + REBASE_OPCODE_DO_REBASE_IMM_TIMES = 0x50 + REBASE_OPCODE_DO_REBASE_ULEB_TIMES = 0x60 + REBASE_OPCODE_DO_REBASE_ADD_ADDR_ULEB = 0x70 + REBASE_OPCODE_DO_REBASE_ULEB_TIMES_SKIPPING_ULEB = 0x80 +) + +// bind table opcode +const ( + BIND_TYPE_POINTER = 1 + BIND_TYPE_TEXT_ABSOLUTE32 = 2 + BIND_TYPE_TEXT_PCREL32 = 3 + + BIND_SPECIAL_DYLIB_SELF = 0 + BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE = -1 + BIND_SPECIAL_DYLIB_FLAT_LOOKUP = -2 + BIND_SPECIAL_DYLIB_WEAK_LOOKUP = -3 + + BIND_OPCODE_MASK = 0xF0 + BIND_IMMEDIATE_MASK = 0x0F + BIND_OPCODE_DONE = 0x00 + BIND_OPCODE_SET_DYLIB_ORDINAL_IMM = 0x10 + BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB = 0x20 + BIND_OPCODE_SET_DYLIB_SPECIAL_IMM = 0x30 + BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM = 0x40 + BIND_OPCODE_SET_TYPE_IMM = 0x50 + BIND_OPCODE_SET_ADDEND_SLEB = 0x60 + BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB = 0x70 + BIND_OPCODE_ADD_ADDR_ULEB = 0x80 + BIND_OPCODE_DO_BIND = 0x90 + BIND_OPCODE_DO_BIND_ADD_ADDR_ULEB = 0xA0 + BIND_OPCODE_DO_BIND_ADD_ADDR_IMM_SCALED = 0xB0 + BIND_OPCODE_DO_BIND_ULEB_TIMES_SKIPPING_ULEB = 0xC0 + BIND_OPCODE_THREADED = 0xD0 + BIND_SUBOPCODE_THREADED_SET_BIND_ORDINAL_TABLE_SIZE_ULEB = 0x00 + BIND_SUBOPCODE_THREADED_APPLY = 0x01 +) + // Mach-O file writing // https://developer.apple.com/mac/library/DOCUMENTATION/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html @@ -279,7 +331,7 @@ var dylib []string var linkoff int64 -func machowrite(arch *sys.Arch, out *OutBuf, linkmode LinkMode) int { +func machowrite(ctxt *Link, arch *sys.Arch, out *OutBuf, linkmode LinkMode) int { o1 := out.Offset() loadsize := 4 * 4 * ndebug @@ -308,11 +360,14 @@ func machowrite(arch *sys.Arch, out *OutBuf, linkmode LinkMode) int { } out.Write32(uint32(len(load)) + uint32(nseg) + uint32(ndebug)) out.Write32(uint32(loadsize)) + flags := uint32(0) if nkind[SymKindUndef] == 0 { - out.Write32(MH_NOUNDEFS) /* flags - no undefines */ - } else { - out.Write32(0) /* flags */ + flags |= MH_NOUNDEFS } + if ctxt.IsPIE() && linkmode == LinkInternal { + flags |= MH_PIE | MH_DYLDLINK + } + out.Write32(flags) /* flags */ if arch.PtrSize == 8 { out.Write32(0) /* reserved */ } @@ -712,15 +767,17 @@ func asmbMacho(ctxt *Link) { s2 := ldr.SymSize(ctxt.ArchSyms.LinkEditPLT) s3 := ldr.SymSize(ctxt.ArchSyms.LinkEditGOT) s4 := ldr.SymSize(ldr.Lookup(".machosymstr", 0)) + s5 := ldr.SymSize(ldr.Lookup(".machorebase", 0)) + s6 := ldr.SymSize(ldr.Lookup(".machobind", 0)) if ctxt.LinkMode != LinkExternal { ms := newMachoSeg("__LINKEDIT", 0) ms.vaddr = uint64(Rnd(int64(Segdata.Vaddr+Segdata.Length), int64(*FlagRound))) - ms.vsize = uint64(s1) + uint64(s2) + uint64(s3) + uint64(s4) + ms.vsize = uint64(s1 + s2 + s3 + s4 + s5 + s6) ms.fileoffset = uint64(linkoff) ms.filesize = ms.vsize - ms.prot1 = 7 - ms.prot2 = 3 + ms.prot1 = 1 + ms.prot2 = 1 } ml := newMachoLoad(ctxt.Arch, LC_SYMTAB, 4) @@ -745,9 +802,23 @@ func asmbMacho(ctxt *Link) { stringtouint32(ml.data[4:], lib) } } + + if ctxt.LinkMode != LinkExternal && ctxt.IsPIE() { + ml := newMachoLoad(ctxt.Arch, LC_DYLD_INFO_ONLY, 10) + ml.data[0] = uint32(linkoff + s1 + s2 + s3 + s4) // rebase off + ml.data[1] = uint32(s5) // rebase size + ml.data[2] = uint32(linkoff + s1 + s2 + s3 + s4 + s5) // bind off + ml.data[3] = uint32(s6) // bind size + ml.data[4] = 0 // weak bind off + ml.data[5] = 0 // weak bind size + ml.data[6] = 0 // lazy bind off + ml.data[7] = 0 // lazy bind size + ml.data[8] = 0 // export + ml.data[9] = 0 // export size + } } - a := machowrite(ctxt.Arch, ctxt.Out, ctxt.LinkMode) + a := machowrite(ctxt, ctxt.Arch, ctxt.Out, ctxt.LinkMode) if int32(a) > HEADR { Exitf("HEADR too small: %d > %d", a, HEADR) } @@ -989,6 +1060,8 @@ func machodysymtab(ctxt *Link) { func doMachoLink(ctxt *Link) int64 { machosymtab(ctxt) + machoDyldInfo(ctxt) + ldr := ctxt.loader // write data that will be linkedit section @@ -996,6 +1069,8 @@ func doMachoLink(ctxt *Link) int64 { s2 := ctxt.ArchSyms.LinkEditPLT s3 := ctxt.ArchSyms.LinkEditGOT s4 := ldr.Lookup(".machosymstr", 0) + s5 := ldr.Lookup(".machorebase", 0) + s6 := ldr.Lookup(".machobind", 0) // Force the linkedit section to end on a 16-byte // boundary. This allows pure (non-cgo) Go binaries @@ -1019,7 +1094,7 @@ func doMachoLink(ctxt *Link) int64 { s4b.AddUint8(0) } - size := int(ldr.SymSize(s1) + ldr.SymSize(s2) + ldr.SymSize(s3) + ldr.SymSize(s4)) + size := int(ldr.SymSize(s1) + ldr.SymSize(s2) + ldr.SymSize(s3) + ldr.SymSize(s4) + ldr.SymSize(s5) + ldr.SymSize(s6)) if size > 0 { 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)) @@ -1029,6 +1104,8 @@ func doMachoLink(ctxt *Link) int64 { ctxt.Out.Write(ldr.Data(s2)) ctxt.Out.Write(ldr.Data(s3)) ctxt.Out.Write(ldr.Data(s4)) + ctxt.Out.Write(ldr.Data(s5)) + ctxt.Out.Write(ldr.Data(s6)) } return Rnd(int64(size), int64(*FlagRound)) @@ -1172,3 +1249,134 @@ func peekMachoPlatform(m *macho.File) (*MachoPlatformLoad, error) { } return nil, nil } + +// A rebase entry tells the dynamic linker the data at sym+off needs to be +// relocated when the in-memory image moves. (This is somewhat like, say, +// ELF R_X86_64_RELATIVE). +// For now, the only kind of entry we support is that the data is an absolute +// address. That seems all we need. +// In the binary it uses a compact stateful bytecode encoding. So we record +// entries as we go and build the table at the end. +type machoRebaseRecord struct { + sym loader.Sym + off int64 +} + +var machorebase []machoRebaseRecord + +func MachoAddRebase(s loader.Sym, off int64) { + machorebase = append(machorebase, machoRebaseRecord{s, off}) +} + +// A bind entry tells the dynamic linker the data at GOT+off should be bound +// to the address of the target symbol, which is a dynamic import. +// For now, the only kind of entry we support is that the data is an absolute +// address, and the source symbol is always the GOT. That seems all we need. +// In the binary it uses a compact stateful bytecode encoding. So we record +// entries as we go and build the table at the end. +type machoBindRecord struct { + off int64 + targ loader.Sym +} + +var machobind []machoBindRecord + +func MachoAddBind(off int64, targ loader.Sym) { + machobind = append(machobind, machoBindRecord{off, targ}) +} + +// Generate data for the dynamic linker, used in LC_DYLD_INFO_ONLY load command. +// See mach-o/loader.h, struct dyld_info_command, for the encoding. +// e.g. https://opensource.apple.com/source/xnu/xnu-6153.81.5/EXTERNAL_HEADERS/mach-o/loader.h +func machoDyldInfo(ctxt *Link) { + ldr := ctxt.loader + rebase := ldr.CreateSymForUpdate(".machorebase", 0) + bind := ldr.CreateSymForUpdate(".machobind", 0) + + if !(ctxt.IsPIE() && ctxt.IsInternal()) { + return + } + + segId := func(seg *sym.Segment) uint8 { + switch seg { + case &Segtext: + return 1 + case &Segrelrodata: + return 2 + case &Segdata: + if Segrelrodata.Length > 0 { + return 3 + } + return 2 + } + panic("unknown segment") + } + + dylibId := func(s loader.Sym) int { + slib := ldr.SymDynimplib(s) + for i, lib := range dylib { + if lib == slib { + return i + 1 + } + } + return BIND_SPECIAL_DYLIB_FLAT_LOOKUP // don't know where it is from + } + + // Rebase table. + // TODO: use more compact encoding. The encoding is stateful, and + // we can use delta encoding. + rebase.AddUint8(REBASE_OPCODE_SET_TYPE_IMM | REBASE_TYPE_POINTER) + for _, r := range machorebase { + seg := ldr.SymSect(r.sym).Seg + off := uint64(ldr.SymValue(r.sym)+r.off) - seg.Vaddr + rebase.AddUint8(REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | segId(seg)) + rebase.AddUleb(off) + + rebase.AddUint8(REBASE_OPCODE_DO_REBASE_IMM_TIMES | 1) + } + rebase.AddUint8(REBASE_OPCODE_DONE) + sz := Rnd(rebase.Size(), 8) + rebase.Grow(sz) + rebase.SetSize(sz) + + // Bind table. + // TODO: compact encoding, as above. + // TODO: lazy binding? + got := ctxt.GOT + seg := ldr.SymSect(got).Seg + gotAddr := ldr.SymValue(got) + bind.AddUint8(BIND_OPCODE_SET_TYPE_IMM | BIND_TYPE_POINTER) + for _, r := range machobind { + off := uint64(gotAddr+r.off) - seg.Vaddr + bind.AddUint8(BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB | segId(seg)) + bind.AddUleb(off) + + d := dylibId(r.targ) + if d > 0 && d < 128 { + bind.AddUint8(BIND_OPCODE_SET_DYLIB_ORDINAL_IMM | uint8(d)&0xf) + } else if d >= 128 { + bind.AddUint8(BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB) + bind.AddUleb(uint64(d)) + } else { // d <= 0 + bind.AddUint8(BIND_OPCODE_SET_DYLIB_SPECIAL_IMM | uint8(d)&0xf) + } + + bind.AddUint8(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM) + // target symbol name as a C string, with _ prefix + bind.AddUint8('_') + bind.Addstring(ldr.SymExtname(r.targ)) + + bind.AddUint8(BIND_OPCODE_DO_BIND) + } + bind.AddUint8(BIND_OPCODE_DONE) + sz = Rnd(bind.Size(), 16) // make it 16-byte aligned, see the comment in doMachoLink + bind.Grow(sz) + bind.SetSize(sz) + + // TODO: export table. + // The symbols names are encoded as a trie. I'm really too lazy to do that + // for now. + // Without it, the symbols are not dynamically exported, so they cannot be + // e.g. dlsym'd. But internal linking is not the default in that case, so + // it is fine. +} diff --git a/src/cmd/link/internal/loader/symbolbuilder.go b/src/cmd/link/internal/loader/symbolbuilder.go index c0c723d7f0..5d37da8ac6 100644 --- a/src/cmd/link/internal/loader/symbolbuilder.go +++ b/src/cmd/link/internal/loader/symbolbuilder.go @@ -420,3 +420,21 @@ func (sb *SymbolBuilder) MakeWritable() { sb.l.SetAttrReadOnly(sb.symIdx, false) } } + +func (sb *SymbolBuilder) AddUleb(v uint64) { + if v < 128 { // common case: 1 byte + sb.AddUint8(uint8(v)) + return + } + for { + c := uint8(v & 0x7f) + v >>= 7 + if v != 0 { + c |= 0x80 + } + sb.AddUint8(c) + if c&0x80 == 0 { + break + } + } +}