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Merge pull request #3482 from cwalther/alloc

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Fix inconsistent supervisor heap
This commit is contained in:
Jeff Epler 2020-10-16 21:31:32 -05:00 committed by GitHub
commit 3c05a8c68c
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1 changed files with 27 additions and 7 deletions
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34
supervisor/shared/memory.c
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@ -33,6 +33,14 @@
#define CIRCUITPY_SUPERVISOR_ALLOC_COUNT (12)
// Using a zero length to mark an unused allocation makes the code a bit shorter (but makes it
// impossible to support zero-length allocations).
#define FREE 0
// The lowest two bits of a valid length are always zero, so we can use them to mark an allocation
// as freed by the client but not yet reclaimed into the FREE middle.
#define HOLE 1
static supervisor_allocation allocations[CIRCUITPY_SUPERVISOR_ALLOC_COUNT];
// We use uint32_t* to ensure word (4 byte) alignment.
uint32_t* low_address;
@ -61,25 +69,31 @@ void free_memory(supervisor_allocation* allocation) {
}
if (allocation->ptr == high_address) {
high_address += allocation->length / 4;
allocation->length = FREE;
for (index++; index < CIRCUITPY_SUPERVISOR_ALLOC_COUNT; index++) {
if (allocations[index].ptr != NULL) {
if (!(allocations[index].length & HOLE)) {
break;
}
// Division automatically shifts out the HOLE bit.
high_address += allocations[index].length / 4;
allocations[index].length = FREE;
}
} else if (allocation->ptr + allocation->length / 4 == low_address) {
low_address = allocation->ptr;
allocation->length = FREE;
for (index--; index >= 0; index--) {
if (allocations[index].ptr != NULL) {
if (!(allocations[index].length & HOLE)) {
break;
}
low_address -= allocations[index].length / 4;
allocations[index].length = FREE;
}
} else {
// Freed memory isn't in the middle so skip updating bounds. The memory will be added to the
// middle when the memory to the inside is freed.
// middle when the memory to the inside is freed. We still need its length, but setting
// only the lowest bit is nondestructive.
allocation->length |= HOLE;
}
allocation->ptr = NULL;
}
supervisor_allocation* allocation_from_ptr(void *ptr) {
@ -99,7 +113,7 @@ supervisor_allocation* allocate_remaining_memory(void) {
}
supervisor_allocation* allocate_memory(uint32_t length, bool high) {
if ((high_address - low_address) * 4 < (int32_t) length || length % 4 != 0) {
if (length == 0 || length % 4 != 0) {
return NULL;
}
uint8_t index = 0;
@ -108,15 +122,21 @@ supervisor_allocation* allocate_memory(uint32_t length, bool high) {
index = CIRCUITPY_SUPERVISOR_ALLOC_COUNT - 1;
direction = -1;
}
supervisor_allocation* alloc;
for (; index < CIRCUITPY_SUPERVISOR_ALLOC_COUNT; index += direction) {
if (allocations[index].ptr == NULL) {
alloc = &allocations[index];
if (alloc->length == FREE && (high_address - low_address) * 4 >= (int32_t) length) {
break;
}
// If a hole matches in length exactly, we can reuse it.
if (alloc->length == (length | HOLE)) {
alloc->length = length;
return alloc;
}
}
if (index >= CIRCUITPY_SUPERVISOR_ALLOC_COUNT) {
return NULL;
}
supervisor_allocation* alloc = &allocations[index];
if (high) {
high_address -= length / 4;
alloc->ptr = high_address;