* [PATCH v2 1/2] tools/nolibc: check for overflow in calloc() without divisions
2026-04-04 11:50 [PATCH v2 0/2] selftests/nolibc: test the memory allocator Thomas Weißschuh
@ 2026-04-04 11:50 ` Thomas Weißschuh
2026-04-04 11:50 ` [PATCH v2 2/2] selftests/nolibc: test the memory allocator Thomas Weißschuh
2026-04-04 12:37 ` [PATCH v2 0/2] " Willy Tarreau
2 siblings, 0 replies; 4+ messages in thread
From: Thomas Weißschuh @ 2026-04-04 11:50 UTC (permalink / raw)
To: Willy Tarreau; +Cc: linux-kernel, 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@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
^ permalink raw reply related [flat|nested] 4+ messages in thread* [PATCH v2 2/2] selftests/nolibc: test the memory allocator
2026-04-04 11:50 [PATCH v2 0/2] selftests/nolibc: test the memory allocator Thomas Weißschuh
2026-04-04 11:50 ` [PATCH v2 1/2] tools/nolibc: check for overflow in calloc() without divisions Thomas Weißschuh
@ 2026-04-04 11:50 ` Thomas Weißschuh
2026-04-04 12:37 ` [PATCH v2 0/2] " Willy Tarreau
2 siblings, 0 replies; 4+ messages in thread
From: Thomas Weißschuh @ 2026-04-04 11:50 UTC (permalink / raw)
To: Willy Tarreau; +Cc: linux-kernel, Thomas Weißschuh
The memory allocator has not seen any testing so far.
Add a simple testcase for it.
Suggested-by: Willy Tarreau <w@1wt.eu>
Link: https://lore.kernel.org/lkml/adDRK8D6YBZgv36H@1wt.eu/
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
This is the proposal from Willy with some improvements:
* Check that calloc() returns zeroed memory
* Test the page-based invariants for all page sizes
* Use named variables instead of hardcoded values
* Fix a segfault
---
tools/testing/selftests/nolibc/nolibc-test.c | 55 ++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/tools/testing/selftests/nolibc/nolibc-test.c b/tools/testing/selftests/nolibc/nolibc-test.c
index 91d95a152568..dd10402267ee 100644
--- a/tools/testing/selftests/nolibc/nolibc-test.c
+++ b/tools/testing/selftests/nolibc/nolibc-test.c
@@ -1555,6 +1555,60 @@ int test_time_types(void)
return 0;
}
+int test_malloc(void)
+{
+ size_t sz_array1, sz_array2, sz_array3;
+ int *array1, *array2, *array3;
+ int pagesize = getpagesize();
+ size_t idx;
+
+ if (pagesize < 0)
+ return 1;
+
+ /* Dependent on the page size, as that is the granularity of our allocator. */
+ sz_array1 = pagesize / 2;
+ array1 = malloc(sz_array1 * sizeof(*array1));
+ if (!array1)
+ return 2;
+
+ for (idx = 0; idx < sz_array1; idx++)
+ array1[idx] = idx;
+
+ sz_array2 = pagesize * 2;
+ array2 = calloc(sz_array2, sizeof(*array2));
+ if (!array2) {
+ free(array1);
+ return 3;
+ }
+
+ for (idx = 0; idx < sz_array2; idx++) {
+ if (array2[idx] != 0) {
+ free(array2);
+ return 4;
+ }
+ array2[idx] = idx + sz_array1;
+ }
+
+ /* Resize array1 into array3 and append array2 at the end. */
+ sz_array3 = sz_array1 + sz_array2;
+ array3 = realloc(array1, sz_array3 * sizeof(*array3));
+ if (!array3) {
+ free(array2);
+ free(array1);
+ return 5;
+ }
+ memcpy(array3 + sz_array1, array2, sizeof(*array2) * sz_array2);
+ free(array2);
+
+ /* The contents must be contiguous now. */
+ for (idx = 0; idx < sz_array3; idx++)
+ if (array3[idx] != (int)idx)
+ return 6;
+
+ free(array3);
+ return 0;
+}
+
int run_stdlib(int min, int max)
{
int test;
@@ -1687,6 +1741,7 @@ int run_stdlib(int min, int max)
CASE_TEST(makedev_big); EXPECT_EQ(1, makedev(0x11223344, 0x55667788), 0x1122355667734488); break;
CASE_TEST(major_big); EXPECT_EQ(1, major(0x1122355667734488), 0x11223344); break;
CASE_TEST(minor_big); EXPECT_EQ(1, minor(0x1122355667734488), 0x55667788); break;
+ CASE_TEST(malloc); EXPECT_ZR(1, test_malloc()); break;
case __LINE__:
return ret; /* must be last */
--
2.53.0
^ permalink raw reply related [flat|nested] 4+ messages in thread