cmd/internal/obj, cmd/link: fix st_other field on PPC64

In PPC64 ELF files, the st_other field indicates the number of
prologue instructions between the global and local entry points.
We add the instructions in the compiler and assembler if -shared is used.
We were assuming that the instructions were present when building a
c-archive or PIE or doing dynamic linking, on the assumption that those
are the cases where the go tool would be building with -shared.
That assumption fails when using some other tool, such as Bazel,
that does not necessarily use -shared in exactly the same way.

This CL records in the object file whether a symbol was compiled
with -shared (this will be the same for all symbols in a given compilation)
and uses that information when setting the st_other field.

Fixes #20290.

Change-Id: Ib2b77e16aef38824871102e3c244fcf04a86c6ea
Reviewed-on: https://go-review.googlesource.com/43051
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Michael Hudson-Doyle <michael.hudson@canonical.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

7 files changed, 21 insertions, 2 deletions

diff --git a/src/cmd/internal/goobj/read.go b/src/cmd/internal/goobj/read.go
index b68fe02eb3..587274401b 100644
--- a/src/cmd/internal/goobj/read.go
+++ b/src/cmd/internal/goobj/read.go
@@ -532,7 +532,7 @@ func (r *objReader) parseObject(prefix []byte) error {
 			f.Args = r.readInt()
 			f.Frame = r.readInt()
 			flags := r.readInt()
-			f.Leaf = flags&1 != 0
+			f.Leaf = flags&(1<<0) != 0
 			f.NoSplit = r.readInt() != 0
 			f.Var = make([]Var, r.readInt())
 			for i := range f.Var {
diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go
index c550d43f26..dc22eacdf4 100644
--- a/src/cmd/internal/obj/objfile.go
+++ b/src/cmd/internal/obj/objfile.go
@@ -338,6 +338,9 @@ func (w *objWriter) writeSym(s *LSym) {
 	if s.ReflectMethod() {
 		flags |= 1 << 2
 	}
+	if ctxt.Flag_shared {
+		flags |= 1 << 3
+	}
 	w.writeInt(flags)
 	w.writeInt(int64(len(s.Func.Autom)))
 	for _, a := range s.Func.Autom {
diff --git a/src/cmd/internal/obj/ppc64/obj9.go b/src/cmd/internal/obj/ppc64/obj9.go
index 72e02d39cf..b1509e3813 100644
--- a/src/cmd/internal/obj/ppc64/obj9.go
+++ b/src/cmd/internal/obj/ppc64/obj9.go
@@ -476,6 +476,11 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 				// generate the addis instruction except as part of the
 				// load of a large constant, and in that case there is no
 				// way to use r12 as the source.
+				//
+				// Note that the same condition is tested in
+				// putelfsym in cmd/link/internal/ld/symtab.go
+				// where we set the st_other field to indicate
+				// the presence of these instructions.
 				q = obj.Appendp(q, c.newprog)
 				q.As = AWORD
 				q.Pos = p.Pos
diff --git a/src/cmd/internal/objabi/doc.go b/src/cmd/internal/objabi/doc.go
index 7b93fc19e5..dc37817a61 100644
--- a/src/cmd/internal/objabi/doc.go
+++ b/src/cmd/internal/objabi/doc.go
@@ -77,6 +77,7 @@
 //		1<<0 leaf
 //		1<<1 C function
 //		1<<2 function may call reflect.Type.Method
+//		1<<3 function compiled with -shared
 //	- nlocal [int]
 //	- local [nlocal automatics]
 //	- pcln [pcln table]
diff --git a/src/cmd/link/internal/ld/link.go b/src/cmd/link/internal/ld/link.go
index 089b4d3d3c..6a1a47e213 100644
--- a/src/cmd/link/internal/ld/link.go
+++ b/src/cmd/link/internal/ld/link.go
@@ -135,6 +135,9 @@ const (
 	// AttrMakeTypelink Amarks types that should be added to the typelink
 	// table. See typelinks.go:typelinks().
 	AttrMakeTypelink
+	// AttrShared marks symbols compiled with the -shared option.
+	AttrShared
+	// 14 attributes defined so far.
 )
 
 func (a Attribute) DuplicateOK() bool      { return a&AttrDuplicateOK != 0 }
@@ -150,6 +153,7 @@ func (a Attribute) OnList() bool           { return a&AttrOnList != 0 }
 func (a Attribute) Local() bool            { return a&AttrLocal != 0 }
 func (a Attribute) ReflectMethod() bool    { return a&AttrReflectMethod != 0 }
 func (a Attribute) MakeTypelink() bool     { return a&AttrMakeTypelink != 0 }
+func (a Attribute) Shared() bool           { return a&AttrShared != 0 }
 
 func (a Attribute) CgoExport() bool {
 	return a.CgoExportDynamic() || a.CgoExportStatic()
diff --git a/src/cmd/link/internal/ld/objfile.go b/src/cmd/link/internal/ld/objfile.go
index c91fe28458..13dde21809 100644
--- a/src/cmd/link/internal/ld/objfile.go
+++ b/src/cmd/link/internal/ld/objfile.go
@@ -258,6 +258,9 @@ overwrite:
 		if flags&(1<<2) != 0 {
 			s.Attr |= AttrReflectMethod
 		}
+		if flags&(1<<3) != 0 {
+			s.Attr |= AttrShared
+		}
 		n := r.readInt()
 		pc.Autom = r.autom[:n:n]
 		if !isdup {
diff --git a/src/cmd/link/internal/ld/symtab.go b/src/cmd/link/internal/ld/symtab.go
index a35ece13ad..78e9dc26bc 100644
--- a/src/cmd/link/internal/ld/symtab.go
+++ b/src/cmd/link/internal/ld/symtab.go
@@ -147,10 +147,13 @@ func putelfsym(ctxt *Link, x *Symbol, s string, t SymbolType, addr int64, go_ *S
 	if x.Type&SHIDDEN != 0 {
 		other = STV_HIDDEN
 	}
-	if (Buildmode == BuildmodeCArchive || Buildmode == BuildmodePIE || ctxt.DynlinkingGo()) && SysArch.Family == sys.PPC64 && typ == STT_FUNC && x.Name != "runtime.duffzero" && x.Name != "runtime.duffcopy" {
+	if SysArch.Family == sys.PPC64 && typ == STT_FUNC && x.Attr.Shared() && x.Name != "runtime.duffzero" && x.Name != "runtime.duffcopy" {
 		// On ppc64 the top three bits of the st_other field indicate how
 		// many instructions separate the global and local entry points. In
 		// our case it is two instructions, indicated by the value 3.
+		// The conditions here match those in preprocess in
+		// cmd/internal/obj/ppc64/obj9.go, which is where the
+		// instructions are inserted.
 		other |= 3 << 5
 	}