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

[Thomas Weißschuh]

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@xxxxxxxxxxxxxx>
---
 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