musl/src/malloc/calloc.c

#include <stdlib.h>
#include <errno.h>

void *__malloc0(size_t);

void *calloc(size_t m, size_t n)
{
	if (n && m > (size_t)-1/n) {
		errno = ENOMEM;
		return 0;
	}
	return __malloc0(n * m);
}
initial check-in, version 0.5.0 2011-02-12 00:22:29 -05:00			`#include <stdlib.h>`
			`#include <errno.h>`

fix calloc when __simple_malloc implementation is used previously, calloc's implementation encoded assumptions about the implementation of malloc, accessing a size_t word just prior to the allocated memory to determine if it was obtained by mmap to optimize out the zero-filling. when __simple_malloc is used (static linking a program with no realloc/free), it doesn't matter if the result of this check is wrong, since all allocations are zero-initialized anyway. but the access could be invalid if it crosses a page boundary or if the pointer is not sufficiently aligned, which can happen for very small allocations. this patch fixes the issue by moving the zero-fill logic into malloc.c with the full malloc, as a new function named __malloc0, which is provided by a weak alias to __simple_malloc (which always gives zero-filled memory) when the full malloc is not in use. 2015-06-22 18:50:09 +00:00			`void *__malloc0(size_t);`

initial check-in, version 0.5.0 2011-02-12 00:22:29 -05:00			`void *calloc(size_t m, size_t n)`
			`{`
			`if (n && m > (size_t)-1/n) {`
			`errno = ENOMEM;`
			`return 0;`
			`}`
fix calloc when __simple_malloc implementation is used previously, calloc's implementation encoded assumptions about the implementation of malloc, accessing a size_t word just prior to the allocated memory to determine if it was obtained by mmap to optimize out the zero-filling. when __simple_malloc is used (static linking a program with no realloc/free), it doesn't matter if the result of this check is wrong, since all allocations are zero-initialized anyway. but the access could be invalid if it crosses a page boundary or if the pointer is not sufficiently aligned, which can happen for very small allocations. this patch fixes the issue by moving the zero-fill logic into malloc.c with the full malloc, as a new function named __malloc0, which is provided by a weak alias to __simple_malloc (which always gives zero-filled memory) when the full malloc is not in use. 2015-06-22 18:50:09 +00:00			`return __malloc0(n * m);`
initial check-in, version 0.5.0 2011-02-12 00:22:29 -05:00			`}`