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

>>>> "tombannink" == tombannink <tombannink(a)gmail.com> writes:

Good catch, thanks Peter. From 880ae1a543f6518f37a32b3af5a734a7b72f9b39 Mon Sep 17 00:00:00 2001 From: Tom Bannink <tombannink(a)gmail.com> Date: Tue, 12 Apr 2022 11:15:41 +0200 Subject: [PATCH] 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.