Hi,
The ARM implementation of memset has a bug when the fill-value is negative or
outside the [0, 255] range. To reproduce:
int main() {
char array[256];
memset(array, -5, 256);
for (int i = 0; i < 256; ++i) {
printf("%d, ", (int)array[i]);
}
return 0;
}
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 other implementations that I checked (aarch64 and x86_64) 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.
How to fix/patch:
In this file:
https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/string/arm/memset.S
Before line 35 (lsl) insert this: uxtb r1, r1
Before line 71 (orr) insert this: uxtb a2, a2
Best regards,
Tom
_______________________________________________
devel mailing list -- devel@uclibc-ng.org
To unsubscribe send an email to devel-le...@uclibc-ng.org
