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, 17 insertions, 5 deletions

diff --git a/src/malloc/malloc.c b/src/malloc/malloc.c
index 991300cc..5a56e0c5 100644
--- a/src/malloc/malloc.c
+++ b/src/malloc/malloc.c
@@ -368,6 +368,8 @@ void *malloc(size_t n)
 	return CHUNK_TO_MEM(c);
 }
 
+weak_alias(malloc, __internal_malloc);
+
 static size_t mal0_clear(char *p, size_t pagesz, size_t n)
 {
 #ifdef __GNUC__
@@ -386,13 +388,21 @@ static size_t mal0_clear(char *p, size_t pagesz, size_t n)
 	}
 }
 
-void *__malloc0(size_t n)
+void *calloc(size_t m, size_t n)
 {
+	if (n && m > (size_t)-1/n) {
+		errno = ENOMEM;
+		return 0;
+	}
+	n *= m;
 	void *p = malloc(n);
-	if (!p || IS_MMAPPED(MEM_TO_CHUNK(p)))
-		return p;
-	if (n >= PAGE_SIZE)
-		n = mal0_clear(p, PAGE_SIZE, n);
+	if (!p) return p;
+	if (malloc == __internal_malloc) {
+		if (IS_MMAPPED(MEM_TO_CHUNK(p)))
+			return p;
+		if (n >= PAGE_SIZE)
+			n = mal0_clear(p, PAGE_SIZE, n);
+	}
 	return memset(p, 0, n);
 }
 
@@ -558,6 +568,8 @@ void free(void *p)
 		bin_chunk(self);
 }
 
+weak_alias(free, __internal_free);
+
 void __malloc_donate(char *start, char *end)
 {
 	size_t align_start_up = (SIZE_ALIGN-1) & (-(uintptr_t)start - OVERHEAD);