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using malloc implementation types/macros/idioms for memalign

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the generated code should be mostly unchanged, except for explicit use
of C_INUSE in place of copying the low bits from existing chunk
headers/footers.

these changes also remove mild UB due to dubious arithmetic on
pointers into imaginary size_t[] arrays.
This commit is contained in:
Rich Felker 2018-04-19 20:45:48 -04:00
parent 23389b1988
commit 3c2cbbe7ba
1 changed files with 22 additions and 20 deletions
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42
src/malloc/memalign.c
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@ -2,49 +2,51 @@
#include <stdint.h>
#include <errno.h>
#include "libc.h"
#include "malloc_impl.h"
void *__memalign(size_t align, size_t len)
{
unsigned char *mem, *new, *end;
size_t header, footer;
unsigned char *mem, *new;
if ((align & -align) != align) {
errno = EINVAL;
return NULL;
return 0;
}
if (len > SIZE_MAX - align) {
errno = ENOMEM;
return NULL;
return 0;
}
if (align <= 4*sizeof(size_t)) {
if (!(mem = malloc(len)))
return NULL;
return mem;
}
if (align <= SIZE_ALIGN)
return malloc(len);
if (!(mem = malloc(len + align-1)))
return NULL;
return 0;
new = (void *)((uintptr_t)mem + align-1 & -align);
if (new == mem) return mem;
header = ((size_t *)mem)[-1];
struct chunk *c = MEM_TO_CHUNK(mem);
struct chunk *n = MEM_TO_CHUNK(new);
if (!(header & 7)) {
((size_t *)new)[-2] = ((size_t *)mem)[-2] + (new-mem);
((size_t *)new)[-1] = ((size_t *)mem)[-1] - (new-mem);
if (IS_MMAPPED(c)) {
/* Apply difference between aligned and original
* address to the "extra" field of mmapped chunk. */
n->psize = c->psize + (new-mem);
n->csize = c->csize - (new-mem);
return new;
}
end = mem + (header & -8);
footer = ((size_t *)end)[-2];
struct chunk *t = NEXT_CHUNK(c);
((size_t *)mem)[-1] = header&7 | new-mem;
((size_t *)new)[-2] = footer&7 | new-mem;
((size_t *)new)[-1] = header&7 | end-new;
((size_t *)end)[-2] = footer&7 | end-new;
/* Split the allocated chunk into two chunks. The aligned part
* that will be used has the size in its footer reduced by the
* difference between the aligned and original addresses, and
* the resulting size copied to its header. A new header and
* footer are written for the split-off part to be freed. */
n->psize = c->csize = C_INUSE | (new-mem);
n->csize = t->psize -= new-mem;
free(mem);
return new;