allow interposition/replacement of allocator (malloc)

replacement is subject to conditions on the replacement functions.
they may only call functions which are async-signal-safe, as specified
either by POSIX or as an implementation-defined extension. if any
allocator functions are replaced, at least malloc, realloc, and free
must be provided. if calloc is not provided, it will behave as
malloc+memset. any of the memalign-family functions not provided will
fail with ENOMEM.

in order to implement the above properties, calloc and __memalign
check that they are using their own malloc or free, respectively.
choice to check malloc or free is based on considerations of
supporting __simple_malloc. in order to make this work, calloc is
split into separate versions for __simple_malloc and full malloc;
commit ba819787ee93ceae94efd274f7849e317c1bff58 already did most of
the split anyway, and completing it saves an extra call frame.

previously, use of -Bsymbolic-functions made dynamic interposition
impossible. now, we are using an explicit dynamic-list, so add
allocator functions to the list. most are not referenced anyway, but
all are added for completeness.

1 files changed, 2 insertions, 4 deletions

diff --git a/src/malloc/memalign.c b/src/malloc/memalign.c
index 006bd21c..35b67599 100644
--- a/src/malloc/memalign.c
+++ b/src/malloc/memalign.c
@@ -3,9 +3,7 @@
 #include <errno.h>
 #include "libc.h"
 
-/* This function should work with most dlmalloc-like chunk bookkeeping
- * systems, but it's only guaranteed to work with the native implementation
- * used in this library. */
+void __internal_free(void *);
 
 void *__memalign(size_t align, size_t len)
 {
@@ -17,7 +15,7 @@ void *__memalign(size_t align, size_t len)
 		return NULL;
 	}
 
-	if (len > SIZE_MAX - align) {
+	if (len > SIZE_MAX - align || free != __internal_free) {
 		errno = ENOMEM;
 		return NULL;
 	}