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 <thanm@google.com>
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 8324a98..a730125 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -930,7 +930,7 @@
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 @@
// 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 @@
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 @@
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 @@
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 f635672..9765ce1 100644
--- a/src/cmd/link/internal/ld/macho.go
+++ b/src/cmd/link/internal/ld/macho.go
@@ -499,16 +499,7 @@
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 @@
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 @@
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 @@
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 @@
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 102b6c5..f68de8f 100644
--- a/src/cmd/link/internal/ld/target.go
+++ b/src/cmd/link/internal/ld/target.go
@@ -74,8 +74,12 @@
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)
}
}
