safe-alloc: fix pointer implementation

The old implementation assumed that all pointers use the same
internal representation, but the C standard doesn’t guarantee
this.  Use void * (pointer) not void ** (pointer-to-pointer) for
the internal functions’ API.  The internal functions now return
NULL if and only if they failed, and the macros translate that
into -1 or 0 to satisfy the existing API.
* doc/safe-alloc.texi (Safe Allocation Macros): Mention overflow.
* lib/safe-alloc.c: Major rewrite.  Now this simply
defines SAFE_ALLOC_INLINE and includes safe-alloc.h.
* lib/safe-alloc.h: Include stddef.h, not stdlib.h.
(SAFE_ALLOC_INLINE): New macro; use Gnulib inline function style.
(safe_alloc_realloc_n): New API, which passes and returns
the pointer, and which returns NULL if and only if failure occurs.
(safe_alloc_check): New function.
(ALLOC, ALLOC_N, ALLOC_N_UNINITIALIZED, REALLOC_N):
Redo using the new API for internal functions, and using calloc
which is good enough since it’s GNU-compatible now.
(FREE): Expand to an expression rather than merely to something
that needs a following ‘;’ to become a statement.
* modules/safe-alloc (Depends-on): Add calloc-gnu.

1 files changed, 2 insertions, 0 deletions

diff --git a/doc/safe-alloc.texi b/doc/safe-alloc.texi
index d40ec65b63..e896e25982 100644
--- a/doc/safe-alloc.texi
+++ b/doc/safe-alloc.texi
@@ -13,6 +13,8 @@ Some of the memory allocation mistakes that are commonly made are
 passing the incorrect number of bytes to @code{malloc}, especially
 when allocating an array,
 @item
+unchecked integer overflow when calculating array sizes,
+@item
 fail to check the return value of @code{malloc} and @code{realloc} for
 errors,
 @item