Commit 5ffe1d8d authored by Damien George's avatar Damien George
Browse files

py/gc: Add MICROPY_GC_CONSERVATIVE_CLEAR option to always zero memory.

There can be stray pointers in memory blocks that are not properly zero'd
after allocation.  This patch adds a new config option to always zero all
allocated memory (via gc_alloc and gc_realloc) and hence help to eliminate
stray pointers.

See issue #2195.
parent d29ca282
......@@ -480,12 +480,17 @@ found:
GC_EXIT();
#if MICROPY_GC_CONSERVATIVE_CLEAR
// be conservative and zero out all the newly allocated blocks
memset((byte*)ret_ptr, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK);
#else
// zero out the additional bytes of the newly allocated blocks
// This is needed because the blocks may have previously held pointers
// to the heap and will not be set to something else if the caller
// doesn't actually use the entire block. As such they will continue
// to point to the heap and may prevent other blocks from being reclaimed.
memset((byte*)ret_ptr + n_bytes, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK - n_bytes);
#endif
#if MICROPY_ENABLE_FINALISER
if (has_finaliser) {
......@@ -713,8 +718,13 @@ void *gc_realloc(void *ptr_in, size_t n_bytes, bool allow_move) {
GC_EXIT();
#if MICROPY_GC_CONSERVATIVE_CLEAR
// be conservative and zero out all the newly allocated blocks
memset((byte*)ptr_in + n_blocks * BYTES_PER_BLOCK, 0, (new_blocks - n_blocks) * BYTES_PER_BLOCK);
#else
// zero out the additional bytes of the newly allocated blocks (see comment above in gc_alloc)
memset((byte*)ptr_in + n_bytes, 0, new_blocks * BYTES_PER_BLOCK - n_bytes);
#endif
#if EXTENSIVE_HEAP_PROFILING
gc_dump_alloc_table();
......
......@@ -117,7 +117,10 @@ void *m_malloc0(size_t num_bytes) {
if (ptr == NULL && num_bytes != 0) {
return m_malloc_fail(num_bytes);
}
// If this config is set then the GC clears all memory, so we don't need to.
#if !MICROPY_GC_CONSERVATIVE_CLEAR
memset(ptr, 0, num_bytes);
#endif
return ptr;
}
......
......@@ -107,6 +107,15 @@
#define MICROPY_ALLOC_GC_STACK_SIZE (64)
#endif
// Be conservative and always clear to zero newly (re)allocated memory in the GC.
// This helps eliminate stray pointers that hold on to memory that's no longer
// used. It decreases performance due to unnecessary memory clearing.
// TODO Do analysis to understand why some memory is not properly cleared and
// find a more efficient way to clear it.
#ifndef MICROPY_GC_CONSERVATIVE_CLEAR
#define MICROPY_GC_CONSERVATIVE_CLEAR (1)
#endif
// Support automatic GC when reaching allocation threshold,
// configurable by gc.threshold().
#ifndef MICROPY_GC_ALLOC_THRESHOLD
......
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