https://github.com/python/cpython/commit/75c6c05fea212330f4b0259602ffae1b2cb91be3
commit: 75c6c05fea212330f4b0259602ffae1b2cb91be3
branch: main
author: Sam Gross <[email protected]>
committer: DinoV <[email protected]>
date: 2024-02-28T12:50:09-08:00
summary:
gh-115891: Fix debug byte filling in free-threaded build (#116018)
The previous code had two bugs. First, the debug offset in the mimalloc
heap includes the two pymalloc debug words, but the pointer passed to
fill_mem_debug does not include them. Second, the current object heap is
correct source for allocations, but not deallocations.
files:
M Objects/obmalloc.c
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 43427d4449eb1a..b2a2286ef22b66 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -2460,14 +2460,23 @@ write_size_t(void *p, size_t n)
}
static void
-fill_mem_debug(debug_alloc_api_t *api, void *data, int c, size_t nbytes)
+fill_mem_debug(debug_alloc_api_t *api, void *data, int c, size_t nbytes,
+ bool is_alloc)
{
#ifdef Py_GIL_DISABLED
if (api->api_id == 'o') {
// Don't overwrite the first few bytes of a PyObject allocation in the
// free-threaded build
_PyThreadStateImpl *tstate = (_PyThreadStateImpl
*)_PyThreadState_GET();
- size_t debug_offset =
tstate->mimalloc.current_object_heap->debug_offset;
+ size_t debug_offset;
+ if (is_alloc) {
+ debug_offset = tstate->mimalloc.current_object_heap->debug_offset;
+ }
+ else {
+ char *alloc = (char *)data - 2*SST; // start of the allocation
+ debug_offset = _mi_ptr_page(alloc)->debug_offset;
+ }
+ debug_offset -= 2*SST; // account for pymalloc extra bytes
if (debug_offset < nbytes) {
memset((char *)data + debug_offset, c, nbytes - debug_offset);
}
@@ -2553,7 +2562,7 @@ _PyMem_DebugRawAlloc(int use_calloc, void *ctx, size_t
nbytes)
memset(p + SST + 1, PYMEM_FORBIDDENBYTE, SST-1);
if (nbytes > 0 && !use_calloc) {
- fill_mem_debug(api, data, PYMEM_CLEANBYTE, nbytes);
+ fill_mem_debug(api, data, PYMEM_CLEANBYTE, nbytes, true);
}
/* at tail, write pad (SST bytes) and serialno (SST bytes) */
@@ -2603,7 +2612,7 @@ _PyMem_DebugRawFree(void *ctx, void *p)
nbytes = read_size_t(q);
nbytes += PYMEM_DEBUG_EXTRA_BYTES - 2*SST;
memset(q, PYMEM_DEADBYTE, 2*SST);
- fill_mem_debug(api, p, PYMEM_DEADBYTE, nbytes);
+ fill_mem_debug(api, p, PYMEM_DEADBYTE, nbytes, false);
api->alloc.free(api->alloc.ctx, q);
}
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