diff options
| author | Tom Bannink <tombannink@gmail.com> | 2022-04-12 13:36:51 +0000 |
|---|---|---|
| committer | Waldemar Brodkorb <wbx@openadk.org> | 2022-04-13 14:17:48 +0200 |
| commit | 592574ae535c35de500f6c3e8d8400d0bb0d985a (patch) | |
| tree | 2f92bea117177e747f95567982de711fcb601eb2 /libc/string/arm/memset.S | |
| parent | 3c34ca798156d58fdea79eef9c0c988f6c8980ff (diff) | |
Fix bug in ARM memset implementation
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 <tombannink@gmail.com>
Acked-by: Peter Korsgaard <peter@korsgaard.com>
Diffstat (limited to 'libc/string/arm/memset.S')
| -rw-r--r-- | libc/string/arm/memset.S | 2 |
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 1: |