On Mon, May 7, 2018 at 9:03 PM, Oliver Pinter <oliver.pin...@hardenedbsd.org > wrote:
> On 5/7/18, Mateusz Guzik <m...@freebsd.org> wrote: > > Author: mjg > > Date: Mon May 7 15:07:28 2018 > > New Revision: 333324 > > URL: https://svnweb.freebsd.org/changeset/base/333324 > > > > Log: > > amd64: replace libkern's memset and memmove with assembly variants > > > > memmove is repurposed bcopy (arguments swapped, return value added) > > The libkern variant is a wrapper around bcopy, so this is a big > > improvement. > > > > memset is repurposed memcpy. The librkern variant is doing fishy stuff, > > including branching on 0 and calling bzero. > > > > Both functions are rather crude and subject to partial depessimization. > > > > This is a soft prerequisite to adding variants utilizing the > > 'Enhanced REP MOVSB/STOSB' bit and let the kernel patch at runtime. > > > > + > > +/* > > + * memset(dst, c, len) > > + * rdi, rsi, rdx > > + */ > > +ENTRY(memset) > > + PUSH_FRAME_POINTER > > + movq %rdi,%r9 > > + movq %rdx,%rcx > > + movq %rsi,%rax > > + shrq $3,%rcx > > + rep > > + stosq > > According to Intel SDM stosq stores the whole RAX into destination, > and then increments the destination register with 8. This > implementation is wrong, since the c is a char, and the The RAX looks > like 000000CC, so the stored patter would be 000000CC * SIZE / 8 * 8 + > CC * SIZE % 8 in destination buffer. > Ye, my bad. Forgot to expand the arg with the multiplication trick. Fixed: https://svnweb.freebsd.org/base?view=revision&revision=333332 -- Mateusz Guzik <mjguzik gmail.com> _______________________________________________ svn-src-head@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
