tools/nolibc/stdlib: Support overflow checking for older compiler versions

Previously, we used __builtin_mul_overflow() to check for overflow in
the multiplication operation in the calloc() function. However, older
compiler versions don't support this built-in. This patch changes the
overflow checking mechanism to make it work on any compiler version
by using a division method to check for overflow. No functional change
intended. While in there, remove the unused variable `void *orig`.

Link: https://lore.kernel.org/lkml/20220330024114.GA18892@1wt.eu
Suggested-by: Willy Tarreau <w@1wt.eu>
Cc: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Acked-by: Willy Tarreau <w@1wt.eu>
Reviewed-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 8fd32eaf8037070a7480b40aeb1b74c4c09e658f..92378c4b9660516255377d2819f72d5eff77afda 100644 (file)
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -128,10 +128,9 @@ void *malloc(size_t len)
 static __attribute__((unused))
 void *calloc(size_t size, size_t nmemb)
 {
-       void *orig;
-       size_t res = 0;
+       size_t x = size * nmemb;
 
-       if (__builtin_expect(__builtin_mul_overflow(nmemb, size, &res), 0)) {
+       if (__builtin_expect(size && ((x / size) != nmemb), 0)) {
                SET_ERRNO(ENOMEM);
                return NULL;
        }
@@ -140,7 +139,7 @@ void *calloc(size_t size, size_t nmemb)
         * No need to zero the heap, the MAP_ANONYMOUS in malloc()
         * already does it.
         */
-       return malloc(res);
+       return malloc(x);
 }
 
 static __attribute__((unused))