Date: Wed, 21 Apr 2021 08:32:54 -0400 From: Jesse DeGuire <jesse.a.deguire@...il.com> To: musl@...ts.openwall.com, Érico Nogueira <ericonr@...root.org> Subject: Re: [PATCH] shorten __aeabi_memset by one instruction On Wed, Apr 21, 2021 at 4:25 AM Szabolcs Nagy <nsz@...t70.net> wrote: > > * Érico Nogueira <ericonr@...root.org> [2021-04-20 16:15:19 -0300]: > > when building for armhf, this makes libc.so text smaller by 4 bytes: > > 606619 to 606615 > > --- > > src/string/arm/__aeabi_memset.s | 3 +-- > > 1 file changed, 1 insertion(+), 2 deletions(-) > > > > diff --git a/src/string/arm/__aeabi_memset.s b/src/string/arm/__aeabi_memset.s > > index f9f60583..980774e8 100644 > > --- a/src/string/arm/__aeabi_memset.s > > +++ b/src/string/arm/__aeabi_memset.s > > @@ -24,8 +24,7 @@ __aeabi_memset: > > cmp r1, #0 > > beq 2f > > adds r1, r0, r1 > > -1: strb r2, [r0] > > - adds r0, r0, #1 > > +1: strb r2, [r0], #1 > > this is not available before armv7 as thumb instruction (and it > has 32bit thumb encoding, so you replace two 16bit instructions > with a 32bit one.) > > normally this asm is compiled in arm mode even if your toolchain > defaults to thumb (i'm not sure why), but if you select a cpu or > arch that only supports thumb then the assembler will try to use > thumb and fail e.g. on -march=armv6-m (but i'm not sure if musl > supports that compilation mode throughout) > Musl currently does not build on Thumb1-only devices (Armv6-m and Armv8-m.base). I submitted a patch some time ago to allow it to build, though life and other obstacles have made me much too slow in actually getting a functioning toolchain together to test it properly. > > cmp r1, r0 > > bne 1b > > 2: bx lr > > -- > > 2.31.1
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