diff options
authorTom Bannink <>2022-04-12 13:36:51 +0000
committerWaldemar Brodkorb <>2022-04-13 14:17:48 +0200
commit592574ae535c35de500f6c3e8d8400d0bb0d985a (patch)
parent3c34ca798156d58fdea79eef9c0c988f6c8980ff (diff)
Fix bug in ARM memset implementationHEADmaster
The ARM implementation of memset has a bug when the fill-value is negative or outside the [0, 255] range. To reproduce: char array[256]; memset(array, -5, 256); This is supposed to fill the array with int8 values -5, -5, -5, ... . On ARM, this does not work because the implementation assumes the high bytes of the fill-value argument are already zero. However in this test case they are filled with 1-bits. The aarch64 and x86_64 implementations do not have this problem: they first convert the fill-value to an unsigned byte following the specification of memset. With GCC one can use `memset(ptr, (-5 & 0xFF), size)` as a workaround, but for clang users that does not work: clang optimizes the `& 0xFF` away because it assumes that memset will do it. Signed-off-by: Tom Bannink <> Acked-by: Peter Korsgaard <>
1 files changed, 2 insertions, 0 deletions
diff --git a/libc/string/arm/memset.S b/libc/string/arm/memset.S
index 412270f50..29c583f16 100644
--- a/libc/string/arm/memset.S
+++ b/libc/string/arm/memset.S
@@ -32,6 +32,7 @@ memset:
cmp r2, #8 @ at least 8 bytes to do?
bcc 2f
+ and r1, r1, #0xFF
lsl r3, r1, #8
orr r1, r3
lsl r3, r1, #16
@@ -68,6 +69,7 @@ memset:
mov a4, a1
cmp a3, $8 @ at least 8 bytes to do?
blo 2f
+ and a2, a2, #0xFF
orr a2, a2, a2, lsl $8
orr a2, a2, a2, lsl $16