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cmd/gc, runtime: treat slices and strings like pointers in garbage collection

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Before, a slice with cap=0 or a string with len=0 might have its
base pointer pointing beyond the actual slice/string data into
the next block. The collector had to ignore slices and strings with
cap=0 in order to avoid misinterpreting the base pointer.

Now, a slice with cap=0 or a string with len=0 still has a base
pointer pointing into the actual slice/string data, no matter what.
The collector can now always scan the pointer, which means
strings and slices are no longer special.

Fixes #8404.

LGTM=khr, josharian
R=josharian, khr, dvyukov
CC=golang-codereviews
https://golang.org/cl/112570044
This commit is contained in:
Russ Cox 2014-08-25 14:38:19 -04:00
parent c6f7c176a3
commit 613383c765
25 changed files with 248 additions and 162 deletions
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15
src/pkg/runtime/stack.c
View file

@ -592,19 +592,8 @@ adjustpointers(byte **scanp, BitVector *bv, AdjustInfo *adjinfo, Func *f)
break;
case BitsMultiWord:
switch(bv->data[(i+1) / (32 / BitsPerPointer)] >> ((i+1) * BitsPerPointer & 31) & 3) {
case BitsString:
// string referents are never on the stack, never need to be adjusted
i++; // skip len
break;
case BitsSlice:
p = scanp[i];
if(minp <= p && p < maxp) {
if(StackDebug >= 3)
runtime·printf("adjust slice %p\n", p);
scanp[i] = p + delta;
}
i += 2; // skip len, cap
break;
default:
runtime·throw("unexpected garbage collection bits");
case BitsEface:
t = (Type*)scanp[i];
if(t != nil && ((t->kind & KindDirectIface) == 0 || (t->kind & KindNoPointers) == 0)) {