From: Willy Tarreau <w@xxxxxx>
[ Upstream commit 1bfbe1f3e96720daf185f03d101f072d69753f88 ]
When building on ARM in thumb mode with gcc-11.3 at -O2 or -O3,
nolibc-test segfaults during the select() tests. It turns out that at
this level, gcc recognizes an opportunity for using memset() to zero
the fd_set, but it miscompiles it because it also recognizes a memset
pattern as well, and decides to call memset() from the memset() code:
000122bc <memset>:
122bc: b510 push {r4, lr}
122be: 0004 movs r4, r0
122c0: 2a00 cmp r2, #0
122c2: d003 beq.n 122cc <memset+0x10>
122c4: 23ff movs r3, #255 ; 0xff
122c6: 4019 ands r1, r3
122c8: f7ff fff8 bl 122bc <memset>
122cc: 0020 movs r0, r4
122ce: bd10 pop {r4, pc}
Simply placing an empty asm() statement inside the loop suffices to
avoid this.
Signed-off-by: Willy Tarreau <w@xxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
tools/include/nolibc/string.h | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/tools/include/nolibc/string.h b/tools/include/nolibc/string.h
index 0932db3817d2..fffdaf6ff467 100644
--- a/tools/include/nolibc/string.h
+++ b/tools/include/nolibc/string.h
@@ -88,8 +88,11 @@ void *memset(void *dst, int b, size_t len)
{
char *p = dst;
- while (len--)
+ while (len--) {
+ /* prevent gcc from recognizing memset() here */
+ asm volatile("");
*(p++) = b;
+ }
return dst;
}
--
2.35.1
