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From: Ammar Faizi <[email protected]>
To: "Paul E. McKenney" <[email protected]>, Willy Tarreau <[email protected]>
Cc: Ammar Faizi <[email protected]>,
	Alviro Iskandar Setiawan <[email protected]>,
	Linux Kernel Mailing List <[email protected]>,
	GNU/Weeb Mailing List <[email protected]>,
	Facebook Kernel Team <[email protected]>
Subject: [PATCH v1 1/2] tools/nolibc/stdlib: Support overflow checking for older compiler versions
Date: Fri, 20 May 2022 00:21:15 +0700	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

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/[email protected]
Suggested-by: Willy Tarreau <[email protected]>
Cc: Alviro Iskandar Setiawan <[email protected]>
Signed-off-by: Ammar Faizi <[email protected]>
---
 tools/include/nolibc/stdlib.h | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 8fd32eaf8037..92378c4b9660 100644
--- 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))
-- 
Ammar Faizi


  reply	other threads:[~2022-05-19 17:21 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-19 17:21 [PATCH v1 0/2] nolibc updates for Linux 5.20 Ammar Faizi
2022-05-19 17:21 ` Ammar Faizi [this message]
2022-05-20  4:19   ` [PATCH v1 1/2] tools/nolibc/stdlib: Support overflow checking for older compiler versions Willy Tarreau
2022-05-20 11:29   ` Alviro Iskandar Setiawan
2022-05-20 17:32     ` Paul E. McKenney
2022-05-19 17:21 ` [PATCH v1 2/2] tools/nolibc/stdio: Add format attribute to enable printf warnings Ammar Faizi
2022-05-20  4:21   ` Willy Tarreau
2022-05-20  4:23 ` [PATCH v1 0/2] nolibc updates for Linux 5.20 Willy Tarreau

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