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 #7338.
Fixes #7347.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/88550043

9 files changed, 14 insertions, 3 deletions

diff --git a/src/cmd/ld/pcln.c b/src/cmd/ld/pcln.c
index bdb139f7a4..b2370f2a91 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 3a2e35a5b2..f392e41680 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 1fd54ed7e6..a694e47291 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 e0cdecea96..270416f0b6 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 9ec799b4f3..448d40f76b 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 c5121ff154..56d416a1a0 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 0f7ab6dd78..91583a3fd4 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 b52b29ca59..0c51e795f5 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 8882eae534..c2e6fa0927 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]