runtime: remove obsolete afterprologue check

Afterprologue check was required when did not know
about return arguments of functions and/or they were not zeroed.
Now 100% precision is required for stacks due to stack copying,
so it must work w/o afterprologue one way or another.
I can limit this change for 1.3 to merely adding a TODO,
but this check is super confusing so I don't want this knowledge to get lost.

LGTM=rsc
R=golang-codereviews, gobot, rsc, khr
CC=golang-codereviews, khr, rsc
https://golang.org/cl/96580045

diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 392da535b1509b6b850bfc32571cf5eeeff6b1b8..50d9feabd060e581c1634622f5fe3704ba9be635 100644 (file)
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -1434,12 +1434,12 @@ runtime·stackmapdata(StackMap *stackmap, int32 n)
 // Scans an interface data value when the interface type indicates
 // that it is a pointer.
 static void
-scaninterfacedata(uintptr bits, byte *scanp, bool afterprologue, void *wbufp)
+scaninterfacedata(uintptr bits, byte *scanp, void *wbufp)
 {
        Itab *tab;
        Type *type;
 
-       if(runtime·precisestack && afterprologue) {
+       if(runtime·precisestack) {
                if(bits == BitsIface) {
                        tab = *(Itab**)scanp;
                        if(tab->type->size <= sizeof(void*) && (tab->type->kind & KindNoPointers))
@@ -1455,7 +1455,7 @@ scaninterfacedata(uintptr bits, byte *scanp, bool afterprologue, void *wbufp)
 
 // Starting from scanp, scans words corresponding to set bits.
 static void
-scanbitvector(Func *f, bool precise, byte *scanp, BitVector *bv, bool afterprologue, void *wbufp)
+scanbitvector(Func *f, bool precise, byte *scanp, BitVector *bv, void *wbufp)
 {
        uintptr word, bits;
        uint32 *wordp;
@@ -1549,7 +1549,7 @@ scanbitvector(Func *f, bool precise, byte *scanp, BitVector *bv, bool afterprolo
                                                        else
                                                                runtime·printf("frame %s @%p: iface %p %p\n", runtime·funcname(f), p, ((uintptr*)p)[0], ((uintptr*)p)[1]);
                                                }
-                                               scaninterfacedata(word & 3, p, afterprologue, wbufp);
+                                               scaninterfacedata(word & 3, p, wbufp);
                                        }
                                        break;
                                }
@@ -1570,7 +1570,6 @@ scanframe(Stkframe *frame, void *wbufp)
        uintptr size;
        uintptr targetpc;
        int32 pcdata;
-       bool afterprologue;
        bool precise;
 
        f = frame->fn;
@@ -1591,36 +1590,33 @@ scanframe(Stkframe *frame, void *wbufp)
 
        // Scan local variables if stack frame has been allocated.
        // Use pointer information if known.
-       afterprologue = (frame->varp > (byte*)frame->sp);
        precise = false;
-       if(afterprologue) {
-               stackmap = runtime·funcdata(f, FUNCDATA_LocalsPointerMaps);
-               if(stackmap == nil) {
-                       // No locals information, scan everything.
-                       size = frame->varp - (byte*)frame->sp;
-                       if(Debug > 2)
-                               runtime·printf("frame %s unsized locals %p+%p\n", runtime·funcname(f), frame->varp-size, size);
-                       enqueue1(wbufp, (Obj){frame->varp - size, size, 0});
-               } else if(stackmap->n < 0) {
-                       // Locals size information, scan just the locals.
-                       size = -stackmap->n;
-                       if(Debug > 2)
-                               runtime·printf("frame %s conservative locals %p+%p\n", runtime·funcname(f), frame->varp-size, size);
-                       enqueue1(wbufp, (Obj){frame->varp - size, size, 0});
-               } else if(stackmap->n > 0) {
-                       // Locals bitmap information, scan just the pointers in
-                       // locals.
-                       if(pcdata < 0 || pcdata >= stackmap->n) {
-                               // don't know where we are
-                               runtime·printf("pcdata is %d and %d stack map entries for %s (targetpc=%p)\n",
-                                       pcdata, stackmap->n, runtime·funcname(f), targetpc);
-                               runtime·throw("scanframe: bad symbol table");
-                       }
-                       bv = runtime·stackmapdata(stackmap, pcdata);
-                       size = (bv.n * PtrSize) / BitsPerPointer;
-                       precise = true;
-                       scanbitvector(f, true, frame->varp - size, &bv, afterprologue, wbufp);
+       stackmap = runtime·funcdata(f, FUNCDATA_LocalsPointerMaps);
+       if(stackmap == nil) {
+               // No locals information, scan everything.
+               size = frame->varp - (byte*)frame->sp;
+               if(Debug > 2)
+                       runtime·printf("frame %s unsized locals %p+%p\n", runtime·funcname(f), frame->varp-size, size);
+               enqueue1(wbufp, (Obj){frame->varp - size, size, 0});
+       } else if(stackmap->n < 0) {
+               // Locals size information, scan just the locals.
+               size = -stackmap->n;
+               if(Debug > 2)
+                       runtime·printf("frame %s conservative locals %p+%p\n", runtime·funcname(f), frame->varp-size, size);
+               enqueue1(wbufp, (Obj){frame->varp - size, size, 0});
+       } else if(stackmap->n > 0) {
+               // Locals bitmap information, scan just the pointers in
+               // locals.
+               if(pcdata < 0 || pcdata >= stackmap->n) {
+                       // don't know where we are
+                       runtime·printf("pcdata is %d and %d stack map entries for %s (targetpc=%p)\n",
+                               pcdata, stackmap->n, runtime·funcname(f), targetpc);
+                       runtime·throw("scanframe: bad symbol table");
                }
+               bv = runtime·stackmapdata(stackmap, pcdata);
+               size = (bv.n * PtrSize) / BitsPerPointer;
+               precise = true;
+               scanbitvector(f, true, frame->varp - size, &bv, wbufp);
        }
 
        // Scan arguments.
@@ -1628,7 +1624,7 @@ scanframe(Stkframe *frame, void *wbufp)
        stackmap = runtime·funcdata(f, FUNCDATA_ArgsPointerMaps);
        if(stackmap != nil) {
                bv = runtime·stackmapdata(stackmap, pcdata);
-               scanbitvector(f, precise, frame->argp, &bv, true, wbufp);
+               scanbitvector(f, precise, frame->argp, &bv, wbufp);
        } else {
                if(Debug > 2)
                        runtime·printf("frame %s conservative args %p+%p\n", runtime·funcname(f), frame->argp, (uintptr)frame->arglen);