liblink: add leaf bit to object file format

Without the leaf bit, the linker cannot record
the correct frame size in the symbol table, and
then stack traces get mangled. (Only for ARM.)

Fixes issue 7338.
Fixes issue 7347.

LGTM=iant
R=iant
CC=golang-codereviews
https://codereview.appspot.com/88550043

9 files changed, 14 insertions, 3 deletions

diff --git a/src/cmd/ld/pcln.c b/src/cmd/ld/pcln.c
index bdb139f7a..b2370f2a9 100644
--- a/src/cmd/ld/pcln.c
+++ b/src/cmd/ld/pcln.c
@@ -112,7 +112,7 @@ pclntab(void)
 {
 	int32 i, nfunc, start, funcstart;
 	LSym *ftab, *s;
-	int32 off, end;
+	int32 off, end, frameptrsize;
 	int64 funcdata_bytes;
 	Pcln *pcln;
 	Pciter it;
@@ -173,7 +173,10 @@ pclntab(void)
 		// when a called function doesn't have argument information.
 		// We need to make sure everything has argument information
 		// and then remove this.
-		off = setuint32(ctxt, ftab, off, ctxt->cursym->locals + PtrSize);
+		frameptrsize = PtrSize;
+		if(ctxt->cursym->leaf)
+			frameptrsize = 0;
+		off = setuint32(ctxt, ftab, off, ctxt->cursym->locals + frameptrsize);
 		
 		if(pcln != &zpcln) {
 			renumberfiles(pcln->file, pcln->nfile, &pcln->pcfile);
diff --git a/src/cmd/link/testdata/autosection.6 b/src/cmd/link/testdata/autosection.6
index 3a2e35a5b..f392e4168 100644
--- a/src/cmd/link/testdata/autosection.6
+++ b/src/cmd/link/testdata/autosection.6
diff --git a/src/cmd/link/testdata/autoweak.6 b/src/cmd/link/testdata/autoweak.6
index 1fd54ed7e..a694e4729 100644
--- a/src/cmd/link/testdata/autoweak.6
+++ b/src/cmd/link/testdata/autoweak.6
diff --git a/src/cmd/link/testdata/dead.6 b/src/cmd/link/testdata/dead.6
index e0cdecea9..270416f0b 100644
--- a/src/cmd/link/testdata/dead.6
+++ b/src/cmd/link/testdata/dead.6
diff --git a/src/cmd/link/testdata/hello.6 b/src/cmd/link/testdata/hello.6
index 9ec799b4f..448d40f76 100644
--- a/src/cmd/link/testdata/hello.6
+++ b/src/cmd/link/testdata/hello.6
diff --git a/src/cmd/link/testdata/layout.6 b/src/cmd/link/testdata/layout.6
index c5121ff15..56d416a1a 100644
--- a/src/cmd/link/testdata/layout.6
+++ b/src/cmd/link/testdata/layout.6
diff --git a/src/cmd/link/testdata/pclntab.6 b/src/cmd/link/testdata/pclntab.6
index 0f7ab6dd7..91583a3fd 100644
--- a/src/cmd/link/testdata/pclntab.6
+++ b/src/cmd/link/testdata/pclntab.6
diff --git a/src/liblink/objfile.c b/src/liblink/objfile.c
index b52b29ca5..0c51e795f 100644
--- a/src/liblink/objfile.c
+++ b/src/liblink/objfile.c
@@ -49,6 +49,7 @@
 //
 //	- args [int]
 //	- locals [int]
+//	- leaf [int]
 //	- nlocal [int]
 //	- local [nlocal automatics]
 //	- pcln [pcln table]
@@ -291,8 +292,11 @@ writesym(Link *ctxt, Biobuf *b, LSym *s)
 		if(s->dupok)
 			Bprint(ctxt->bso, "dupok ");
 		Bprint(ctxt->bso, "size=%lld value=%lld", (vlong)s->size, (vlong)s->value);
-		if(s->type == STEXT)
+		if(s->type == STEXT) {
 			Bprint(ctxt->bso, " args=%#llux locals=%#llux", (uvlong)s->args, (uvlong)s->locals);
+			if(s->leaf)
+				Bprint(ctxt->bso, " leaf");
+		}
 		Bprint(ctxt->bso, "\n");
 		for(p=s->text; p != nil; p = p->link)
 			Bprint(ctxt->bso, "\t%#06ux %P\n", (int)p->pc, p);
@@ -346,6 +350,7 @@ writesym(Link *ctxt, Biobuf *b, LSym *s)
 	if(s->type == STEXT) {
 		wrint(b, s->args);
 		wrint(b, s->locals);
+		wrint(b, s->leaf);
 		n = 0;
 		for(a = s->autom; a != nil; a = a->link)
 			n++;
@@ -566,6 +571,7 @@ readsym(Link *ctxt, Biobuf *f, char *pkg, char *pn)
 	if(s->type == STEXT) {
 		s->args = rdint(f);
 		s->locals = rdint(f);
+		s->leaf = rdint(f);
 		n = rdint(f);
 		for(i=0; i<n; i++) {
 			a = emallocz(sizeof *a);
diff --git a/src/pkg/debug/goobj/read.go b/src/pkg/debug/goobj/read.go
index 8882eae53..c2e6fa092 100644
--- a/src/pkg/debug/goobj/read.go
+++ b/src/pkg/debug/goobj/read.go
@@ -190,6 +190,7 @@ type Var struct {
 type Func struct {
 	Args     int        // size in bytes of of argument frame: inputs and outputs
 	Frame    int        // size in bytes of local variable frame
+	Leaf     bool       // function omits save of link register (ARM)
 	Var      []Var      // detail about local variables
 	PCSP     Data       // PC → SP offset map
 	PCFile   Data       // PC → file number map (index into File)
@@ -621,6 +622,7 @@ func (r *objReader) parseObject(prefix []byte) error {
 			s.Func = f
 			f.Args = r.readInt()
 			f.Frame = r.readInt()
+			f.Leaf = r.readInt() != 0
 			f.Var = make([]Var, r.readInt())
 			for i := range f.Var {
 				v := &f.Var[i]