[PATCH] avoid pointer arithmetic involving NULL in FLEX_ALLOC_MEM
- From
René Scharfe <l.s.r@web.de>
- Date
- Oct 15, 2016, 16:23 UTC
- Message-ID
- <ccb15072-d949-fc84-ee45-45ba013f53c4@web.de>
Calculating offsets involving a NULL pointer is undefined. It works in practice (for now?), but we should not rely on it. Allocate first and then simply refer to the flexible array member by its name instead of performing pointer arithmetic up front. The resulting code is slightly shorter, easier to read and doesn't rely on undefined behaviour.
NB: The cast to a (non-const) void pointer is necessary to keep support for flexible array members declared as const.
Signed-off-by: Rene Scharfe <l.s.r@web.de> --- This patch allows the test suite to largely pass (t7063 still fails) for clang 3.8 with -fsanitize=undefined and -DNO_UNALIGNED_LOADS.
git-compat-util.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/git-compat-util.h b/git-compat-util.h index 43718da..f964e36 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -851,8 +851,9 @@ static inline void copy_array(void *dst, const void *src, size_t n, size_t size) * times, and it must be assignable as an lvalue. */ #define FLEX_ALLOC_MEM(x, flexname, buf, len) do { \ - (x) = NULL; /* silence -Wuninitialized for offset calculation */ \ - (x) = xalloc_flex(sizeof(*(x)), (char *)(&((x)->flexname)) - (char *)(x), (buf), (len)); \ + size_t flex_array_len_ = (len); \ + (x) = xcalloc(1, st_add3(sizeof(*(x)), flex_array_len_, 1)); \ + memcpy((void *)(x)->flexname, (buf), flex_array_len_); \ } while (0) #define FLEXPTR_ALLOC_MEM(x, ptrname, buf, len) do { \ (x) = xalloc_flex(sizeof(*(x)), sizeof(*(x)), (buf), (len)); \
-- 2.10.1