Date: Sun, 18 Jun 2017 21:11:04 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: [PATCH] fix arm run-time abi string functions * Szabolcs Nagy <nsz@...t70.net> [2017-06-18 20:50:07 +0200]: > * Alexander Monakov <amonakov@...ras.ru> [2017-06-18 15:14:51 +0300]: > > Sorry for a bit of extreme nit-picking, but > > > > On Tue, 21 Feb 2017, Szabolcs Nagy wrote: > > > +__aeabi_memmove8: > > > +__aeabi_memmove4: > > > +__aeabi_memmove: > > > + cmp r0, r1 > > > + bls 2f > > > + cmp r2, #0 > > > + bxeq lr > > > + add r0, r0, r2 > > > + add r2, r1, r2 > > > +1: ldrb r3, [r2, #-1]! > > > + cmp r1, r2 > > > + strb r3, [r0, #-1]! > > > + bne 1b > > > + bx lr > > > +__aeabi_memcpy8: > > > +__aeabi_memcpy4: > > > +__aeabi_memcpy: > > > +2: cmp r2, #0 > > > + bxeq lr > > > + sub r0, r0, #1 > > > + add r2, r1, r2 > > > +1: ldrb r3, [r1], #1 > > > + cmp r1, r2 > > > + strb r3, [r0, #1]! > > > + bne 1b > > > + bx lr > > > > here it's possible to hoist and deduplicate 'cmp r2, #0; bxeq lr' by placing it > > prior to the direction check. > > > > i dont think there is a difference > (either way, both functions need to do this cmp once, > the executed insns are the same you just changed the > ordering a bit) > > > > +__aeabi_memclr8: > > > +__aeabi_memclr4: > > > +__aeabi_memclr: > > > + mov r2, #0 > > > +__aeabi_memset8: > > > +__aeabi_memset4: > > > +__aeabi_memset: > > > + cmp r1, #0 > > > + bxeq lr > > > + and r2, r2, #255 > > > > here I don't see why the 'and' is useful, I don't think the following strb > > needs high bits cleared? > > > > indeed > (i wrote naive c code and compiled with gcc.. > for some reason it did the and so i kept it, but > strb seems to ignore top bits according to spec) > > shall i resend without and? > i cannot reproduce the gcc issue with and now, however.. > > > + add r1, r0, r1 > > > +1: strb r2, [r0], #1 it seems strb with postindex+writeback is armv6t, so does not work in armv4t, i'll send an updated patch. > > > + cmp r1, r0 > > > + bne 1b > > > + bx lr > > > > Alexander
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