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, 11 insertions, 1 deletions

diff --git a/src/malloc/lite_malloc.c b/src/malloc/lite_malloc.c
index 701f60b4..29cccb10 100644
--- a/src/malloc/lite_malloc.c
+++ b/src/malloc/lite_malloc.c
@@ -47,4 +47,14 @@ static void *__simple_malloc(size_t n)
 }
 
 weak_alias(__simple_malloc, malloc);
-weak_alias(__simple_malloc, __malloc0);
+
+static void *__simple_calloc(size_t m, size_t n)
+{
+	if (n && m > (size_t)-1/n || malloc != __simple_malloc) {
+		errno = ENOMEM;
+		return 0;
+	}
+	return __simple_malloc(n * m);
+}
+
+weak_alias(__simple_calloc, calloc);