[uclibc-ng-devel] Re: Bug in memset on ARM

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/mems… Before line 35 (lsl) insert this: uxtb r1, r1 Before line 71 (orr) insert this: uxtb a2, a2