[PATCH v2 1/2] tools/nolibc: check for overflow in calloc() without divisions

Thomas Weißschuh
2026-04-04T11:50:28Z

On some architectures without native division instructions
the division can generate calls into libgcc/compiler-rt.
This library might not be available, so its use should be avoided.

Use the compiler builtin to check for overflows without needing a
division. The builtin has been available since GCC 3 and clang 3.8.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
tools/include/nolibc/stdlib.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 2113a8e7695d..1816c2368b68 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -145,9 +145,9 @@ void *malloc(size_t len)
static __attribute__((unused))
void *calloc(size_t size, size_t nmemb)
{
- size_t x = size * nmemb;
+ size_t x;

- if (__builtin_expect(size && ((x / size) != nmemb), 0)) {
+ if (__builtin_expect(__builtin_mul_overflow(size, nmemb, &x), 0)) {
SET_ERRNO(ENOMEM);
return NULL;
}

--
2.53.0