runtime: use a distinct pattern to mark free blocks in need of zeroing

R=golang-dev, dvyukov, khr, cshapiro
CC=golang-dev
https://golang.org/cl/8392043

diff --git a/src/pkg/runtime/malloc.goc b/src/pkg/runtime/malloc.goc
index a30129ffc145ba5c005e620f2f46c650de9f97e2..f1d25a793f82b67f957a6cca34cbb345ae6276d3 100644 (file)
--- a/src/pkg/runtime/malloc.goc
+++ b/src/pkg/runtime/malloc.goc
@@ -160,7 +160,7 @@ runtime·free(void *v)
        if(sizeclass == 0) {
                // Large object.
                size = s->npages<<PageShift;
-               *(uintptr*)(s->start<<PageShift) = 1;   // mark as "needs to be zeroed"
+               *(uintptr*)(s->start<<PageShift) = (uintptr)0xfeedfeedfeedfeedll;       // mark as "needs to be zeroed"
                // Must mark v freed before calling unmarkspan and MHeap_Free:
                // they might coalesce v into other spans and change the bitmap further.
                runtime·markfreed(v, size);
@@ -170,7 +170,7 @@ runtime·free(void *v)
                // Small object.
                size = runtime·class_to_size[sizeclass];
                if(size > sizeof(uintptr))
-                       ((uintptr*)v)[1] = 1;   // mark as "needs to be zeroed"
+                       ((uintptr*)v)[1] = (uintptr)0xfeedfeedfeedfeedll;       // mark as "needs to be zeroed"
                // Must mark v freed before calling MCache_Free:
                // it might coalesce v and other blocks into a bigger span
                // and change the bitmap further.

diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c
index 2d129eb8edfea2efa08e165ded924fe0d79e8510..caf1b10e346ac31e197e7e6f2f0a9c3bbd5d8dfa 100644 (file)
--- a/src/pkg/runtime/mgc0.c
+++ b/src/pkg/runtime/mgc0.c
@@ -1607,7 +1607,7 @@ sweepspan(ParFor *desc, uint32 idx)
                if(cl == 0) {
                        // Free large span.
                        runtime·unmarkspan(p, 1<<PageShift);
-                       *(uintptr*)p = 1;       // needs zeroing
+                       *(uintptr*)p = (uintptr)0xdeaddeaddeaddeadll;   // needs zeroing
                        runtime·MHeap_Free(runtime·mheap, s, 1);
                        c->local_alloc -= size;
                        c->local_nfree++;
@@ -1622,7 +1622,7 @@ sweepspan(ParFor *desc, uint32 idx)
                                break;
                        }
                        if(size > sizeof(uintptr))
-                               ((uintptr*)p)[1] = 1;   // mark as "needs to be zeroed"
+                               ((uintptr*)p)[1] = (uintptr)0xdeaddeaddeaddeadll;       // mark as "needs to be zeroed"
                        
                        end->next = (MLink*)p;
                        end = (MLink*)p;