[go] cmd/link: use correct alignment for type descriptors on AIX
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Ian Lance Taylor (Gerrit)
Jan 30, 2026, 10:13:05 PM (7 days ago) Jan 30
to Cherry Mui, goph...@pubsubhelper.golang.org, Ian Lance Taylor, golang-co...@googlegroups.com
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Commit message
cmd/link: use correct alignment for type descriptors on AIX
CL 724261 changed the linker to put all type descriptors that
are used for typelinks in a single list. This caused trouble on AIX when
linking externally, because the AIX linker aligns symbols individually,
rather than honoring the layout of the object file generated by the
internal linker.
I fixed internal linking problems with CL 740220,
but that just made things worse for the external linker.
This CL rolls back 740220, and adds commentary.
With this CL we force a smaller alignment for type descriptors,
use the same alignment for runtime.types and type:*,
and use a consistent size for runtime.types in all cases.
With this change all the type descriptor related code
passes again on AIX, except for the new TestTypePlacement test
which I will fix in a followup CL.
Change-Id: I9f25847eb0588001cb4ce453f211a655400d6a59
Change diff
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 683df3b..e2f24d9 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -1469,6 +1469,8 @@
// fixZeroSizedSymbols gives a few special symbols with zero size some space.
func fixZeroSizedSymbols(ctxt *Link) {
+ ldr := ctxt.loader
+
// The values in moduledata are filled out by relocations
// pointing to the addresses of these special symbols.
// Typically these symbols have no size and are not laid
@@ -1492,11 +1494,29 @@
// aren't real symbols, their alignment might not match the
// first symbol alignment. Therefore, there are explicitly put at the
// beginning of their section with the same alignment.
+
+ defineRuntimeTypes := func() {
+ types := ldr.CreateSymForUpdate("runtime.types", 0)
+ types.SetType(sym.STYPE)
+ types.SetSize(8)
+ types.SetAlign(int32(ctxt.Arch.PtrSize))
+ ldr.SetAttrSpecial(types.Sym(), false)
+ }
+
if !(ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin) && !(ctxt.HeadType == objabi.Haix && ctxt.LinkMode == LinkExternal) {
+
+ // On AIX, below, we give runtime.types a size.
+ // That means that the type descriptors will actually
+ // follow runtime.types plus that size.
+ // To simplify matters for the runtime,
+ // always give runtime.types a size.
+ if ctxt.HeadType == objabi.Haix {
+ defineRuntimeTypes()
+ }
+
return
}
- ldr := ctxt.loader
bss := ldr.CreateSymForUpdate("runtime.bss", 0)
bss.SetSize(8)
ldr.SetAttrSpecial(bss.Sym(), false)
@@ -1530,10 +1550,7 @@
enoptrdata := ldr.CreateSymForUpdate("runtime.enoptrdata", 0)
ldr.SetAttrSpecial(enoptrdata.Sym(), false)
- types := ldr.CreateSymForUpdate("runtime.types", 0)
- types.SetType(sym.STYPE)
- types.SetSize(8)
- ldr.SetAttrSpecial(types.Sym(), false)
+ defineRuntimeTypes()
etypes := ldr.CreateSymForUpdate("runtime.etypes", 0)
etypes.SetType(sym.STYPE)
@@ -2182,11 +2199,19 @@
createRelroSect := func(name string, symn sym.SymKind) *sym.Section {
sect := state.allocateNamedDataSection(segRelro, genrelrosecname(name), []sym.SymKind{symn}, relroPerm)
- if symn == sym.STYPE {
+ if symn == sym.STYPE && ctxt.HeadType != objabi.Haix {
// Skip forward so that no type
// reference uses a zero offset.
// This is unlikely but possible in small
// programs with no other read-only data.
+ //
+ // Don't skip forward on AIX because the external
+ // linker, when used, will align symbols itself.
+ // The external linker won't know about this skip,
+ // and will mess up the constant offsets we need
+ // within the type section. On AIX we just live
+ // with the possibility of a broken program
+ // if there is no other read-only data.
state.datsize++
}
@@ -2344,6 +2369,10 @@
tail = s
continue
}
+ } else if ctxt.HeadType == objabi.Haix && ldr.SymName(s) == "runtime.types" {
+ // We always use runtime.types on AIX.
+ // See the comment in fixZeroSizedSymbols.
+ head = s
}
}
zerobase = ldr.Lookup("runtime.zerobase", 0)
diff --git a/src/cmd/link/internal/ld/symtab.go b/src/cmd/link/internal/ld/symtab.go
index 142fb15..b88cfd3 100644
--- a/src/cmd/link/internal/ld/symtab.go
+++ b/src/cmd/link/internal/ld/symtab.go
@@ -528,6 +528,15 @@
if symtype != 0 {
ldr.SetCarrierSym(s, symtype)
}
+ if ctxt.HeadType == objabi.Haix {
+ // The default alignment is currently 0x20,
+ // which the AIX external linker doesn't
+ // seem to support. To get consistent
+ // alignment on AIX, force alignment to 8.
+ if symalign(ldr, s) > 8 {
+ ldr.SetSymAlign(s, 8)
+ }
+ }
}
}
diff --git a/src/cmd/link/internal/ld/xcoff.go b/src/cmd/link/internal/ld/xcoff.go
index 8edd4cc..e263500 100644
--- a/src/cmd/link/internal/ld/xcoff.go
+++ b/src/cmd/link/internal/ld/xcoff.go
@@ -586,14 +586,9 @@
case sym.SRODATA, sym.SRODATARELRO, sym.SSTRING:
// Nothing to do
case sym.STYPE:
- if ctxt.UseRelro() && (ctxt.BuildMode == BuildModeCArchive || ctxt.BuildMode == BuildModeCShared || ctxt.BuildMode == BuildModePIE) {
- return
- }
- if !ctxt.DynlinkingGo() {
- // runtime.types size must be removed, as it's a real symbol.
- tsize := ldr.SymSize(ldr.Lookup("runtime.types", 0))
- outerSymSize["type:*"] = size - tsize
- }
+ // runtime.types size must be removed, as it's a real symbol.
+ tsize := ldr.SymSize(ldr.Lookup("runtime.types", 0))
+ outerSymSize["type:*"] = size - tsize
case sym.SGOSTRING:
outerSymSize["go:string.*"] = size
case sym.SGOFUNC:
diff --git a/src/runtime/type.go b/src/runtime/type.go
index 78018fd..82ac512 100644
--- a/src/runtime/type.go
+++ b/src/runtime/type.go
@@ -520,6 +520,11 @@
// We have to increment by 1 to match the increment done in
// cmd/link/internal/data.go createRelroSect in allocateDataSections.
+ //
+ // We don't do that increment on AIX, but on AIX we need to adjust
+ // for the fact that the runtime.types symbol has a size of 8,
+ // and the type descriptors will follow that. This increment,
+ // followed by the forced alignment to 8, will do that.
td++
etypedesc := md.types + md.typedesclen
@@ -528,6 +533,9 @@
// 0x20 does not make sense.
if GOARCH == "arm" {
td = alignUp(td, 0x8)
+ } else if GOOS == "aix" {
+ // The alignment of 8 is forced in the linker on AIX.
+ td = alignUp(td, 0x8)
} else {
td = alignUp(td, 0x20)
}
Change information
Files:
- M src/cmd/link/internal/ld/data.go
- M src/cmd/link/internal/ld/symtab.go
- M src/cmd/link/internal/ld/xcoff.go
- M src/runtime/type.go
Change size: M
Delta: 4 files changed, 55 insertions(+), 14 deletions(-)
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Ian Lance Taylor (Gerrit)
Jan 30, 2026, 10:13:18 PM (7 days ago) Jan 30
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Ian Lance Taylor (Gerrit)
Jan 30, 2026, 10:45:51 PM (7 days ago) Jan 30
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Ian Lance Taylor (Gerrit)
Jan 30, 2026, 10:46:03 PM (7 days ago) Jan 30
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Gopher Robot . resolved
Gopher RobotSlowBots beginning. Status page: https://farmer.golang.org/try?commit=9c39d85d
Ian Lance Taylor1 of 1 SlowBots failed.
Failed on aix-ppc64: https://storage.googleapis.com/go-build-log/9c39d85d/aix-ppc64_765f2949.logConsult https://build.golang.org/ to see whether they are new failures. Keep in mind that TryBots currently test *exactly* your git commit, without rebasing. If your commit's git parent is old, the failure might've already been fixed.
SlowBot builds that ran:
- aix-ppc64
The tests failed on AIX for reasons unrelated to this CL. Still, it's possible to see that the tests ran much better than earlier atttemps.
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Ian Lance Taylor (Gerrit)
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Ian Lance Taylor (Gerrit)
Feb 2, 2026, 1:00:42 AM (5 days ago) Feb 2
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Cherry Mui (Gerrit)
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Ian Lance Taylor (Gerrit)
Feb 6, 2026, 6:04:59 PM (10 hours ago) Feb 6
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Michael Pratt (Gerrit)
Feb 6, 2026, 6:29:34 PM (9 hours ago) Feb 6
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Gopher Robot (Gerrit)
Feb 6, 2026, 6:30:45 PM (9 hours ago) Feb 6
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Change information
Commit message:
cmd/link: use correct alignment for type descriptors on AIX
CL 724261 changed the linker to put all type descriptors that
are used for typelinks in a single list. This caused trouble on AIX when
linking externally, because the AIX linker aligns symbols individually,
rather than honoring the layout of the object file generated by the
internal linker.
I fixed internal linking problems with CL 740220,
but that just made things worse for the external linker.
This CL rolls back 740220, and adds commentary.
With this CL we force a smaller alignment for type descriptors,
use the same alignment for runtime.types and type:*,
and use a consistent size for runtime.types in all cases.
With this change all the type descriptor related code
passes again on AIX, except for the new TestTypePlacement test
which I will fix in a followup CL.
Fixes #77400
Change-Id: I9f25847eb0588001cb4ce453f211a655400d6a59
Reviewed-on: https://go-review.googlesource.com/c/go/+/740820
Reviewed-by: Michael Pratt <mpr...@google.com>
Reviewed-by: Cherry Mui <cher...@google.com>
Auto-Submit: Ian Lance Taylor <ia...@golang.org>
LUCI-TryBot-Result: Go LUCI <golang...@luci-project-accounts.iam.gserviceaccount.com>
Files:
- M src/cmd/link/internal/ld/data.go
- M src/cmd/link/internal/ld/symtab.go
- M src/cmd/link/internal/ld/xcoff.go
- M src/runtime/type.go
Change size: M
Delta: 4 files changed, 55 insertions(+), 14 deletions(-)
Branch: refs/heads/master
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Code-Review: +2 by Cherry Mui, +1 by Michael Pratt
TryBots-Pass: LUCI-TryBot-Result+1 by Go LUCI
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