cmd/link, runtime: record size of itabs

We were depending on runtime.etypes immediately following the itabs.
However, on AIX, runtime.etypes, as a zero-sized symbol, can float
when using external linking. It won't necessarily stay right at the
end of the itabs. Rather than worry about this, just record the size
of the itab data.

In practice it almost always works on AIX, but it fails the runtime
test TestSchedPauseMetrics/runtime/debug.WriteHeapDump,
which fails when iterating over all the itabs.

Tested on AIX. This should fix AIX on the build dashboard.

Change-Id: Id3a113b75b93fa8440c047e92f764ab81423df48
Reviewed-on: https://go-review.googlesource.com/c/go/+/760203
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>

5 files changed, 19 insertions, 2 deletions

diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index bf2bac18af..773efb421f 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -2549,6 +2549,19 @@ func (state *dodataState) dodataSect(ctxt *Link, symn sym.SymKind, syms []loader
 			su.SetUint(ctxt.Arch, ctxt.moduledataItabOffset, uint64(typeSize))
 		}
 
+		itabSize := int64(0)
+		for ; i < len(sl); i++ {
+			itabSize = Rnd(itabSize, int64(symalign(ldr, sl[i].sym)))
+			itabSize += sl[i].sz
+		}
+
+		if ctxt.moduledataItabSizeOffset == 0 {
+			Errorf("internal error: phase error: moduledataItabSizeOffset not set in dodataSect")
+		} else {
+			su := ldr.MakeSymbolUpdater(ctxt.Moduledata)
+			su.SetUint(ctxt.Arch, ctxt.moduledataItabSizeOffset, uint64(itabSize))
+		}
+
 	default:
 		sort.Slice(sl, sortFn)
 	}
diff --git a/src/cmd/link/internal/ld/link.go b/src/cmd/link/internal/ld/link.go
index 1ab54dc918..c0d20680a7 100644
--- a/src/cmd/link/internal/ld/link.go
+++ b/src/cmd/link/internal/ld/link.go
@@ -98,6 +98,7 @@ type Link struct {
 
 	moduledataTypeDescOffset int64
 	moduledataItabOffset     int64
+	moduledataItabSizeOffset int64
 
 	PackageFile  map[string]string
 	PackageShlib map[string]string
diff --git a/src/cmd/link/internal/ld/symtab.go b/src/cmd/link/internal/ld/symtab.go
index ddc2278593..37ab0fa582 100644
--- a/src/cmd/link/internal/ld/symtab.go
+++ b/src/cmd/link/internal/ld/symtab.go
@@ -638,6 +638,8 @@ func (ctxt *Link) symtab(pcln *pclntab) []sym.SymKind {
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.etypes", 0))
 	ctxt.moduledataItabOffset = moduledata.Size()
 	moduledata.AddUint(ctxt.Arch, 0) // filled in by dodataSect
+	ctxt.moduledataItabSizeOffset = moduledata.Size()
+	moduledata.AddUint(ctxt.Arch, 0) // filled in by dodataSect
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.rodata", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("go:func.*", 0))
 	moduledata.AddAddr(ctxt.Arch, ldr.Lookup("runtime.epclntab", 0))
diff --git a/src/runtime/iface.go b/src/runtime/iface.go
index 5e58db6108..009f104327 100644
--- a/src/runtime/iface.go
+++ b/src/runtime/iface.go
@@ -269,7 +269,8 @@ func itabsinit() {
 // This is an optimization to let us skip creating itabs we already have.
 func addModuleItabs(md *moduledata) {
 	p := md.types + md.itaboffset
-	for p < md.etypes {
+	end := p + md.itabsize
+	for p < end {
 		itab := (*itab)(unsafe.Pointer(p))
 		itabAdd(itab)
 		p += uintptr(itab.Size())
diff --git a/src/runtime/symtab.go b/src/runtime/symtab.go
index f5e69c26ec..aa84a6f94e 100644
--- a/src/runtime/symtab.go
+++ b/src/runtime/symtab.go
@@ -420,7 +420,7 @@ type moduledata struct {
 	covctrs, ecovctrs          uintptr
 	end, gcdata, gcbss         uintptr
 	types, typedesclen, etypes uintptr
-	itaboffset                 uintptr
+	itaboffset, itabsize       uintptr
 	rodata                     uintptr
 	gofunc                     uintptr // go.func.*
 	epclntab                   uintptr