From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-1.7 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3, RCVD_IN_MSPIKE_WL,URIBL_BLACK autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 9542 invoked from network); 21 Apr 2021 19:02:31 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 21 Apr 2021 19:02:31 -0000 Received: (qmail 7658 invoked by uid 550); 21 Apr 2021 19:02:25 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 7637 invoked from network); 21 Apr 2021 19:02:24 -0000 X-Virus-Scanned: Debian amavisd-new at disroot.org DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=disroot.org; s=mail; t=1619031724; bh=tRNAMJlHHN96uQxJp6ihRkqiT1KazohldiYsZFxl030=; h=Subject:To:References:From:Date:In-Reply-To; b=dtkvilInnN826vH/bbd1uo/ez/+BwfBJ0CS4ePpNBbdx2+lMNI5x+GDngCBEYISXb CApfBxRz7jkOaMrD/xz9yzLN2L1zxVgKm/ZKfK35E/58Ga6rSUbuwWoCi5u860uH0d RMjjElyjsJXuR2WGiMPX611KPOxti8bDGrEQvRjOmih09qf9XESdIhBqNnm4TYVmrn 0Mp3DCsAaN+lstp0hAZkiw85m0tB3qIyttLS2UhMnoZhPJP+Q9gwucMGb/HgB5tVHP 4ZGWExJwAdAtB/XLWNp1cMLhpbDAtOLMl/fH1W1XfOfUHyOCv3PWmZEqKPnuvHfBzV RwI5mohFaLitQ== To: musl@lists.openwall.com References: <20210420191519.23822-1-ericonr@disroot.org> <20210420191519.23822-5-ericonr@disroot.org> <20210421082458.GI2799122@port70.net> <20210421173848.GS2546@brightrain.aerifal.cx> From: =?UTF-8?Q?=c3=89rico_Nogueira?= Message-ID: <87873c52-bd86-65e8-d9ae-26d0c1dbfdef@disroot.org> Date: Wed, 21 Apr 2021 16:02:00 -0300 Mime-Version: 1.0 In-Reply-To: <20210421173848.GS2546@brightrain.aerifal.cx> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Subject: Re: [musl] [PATCH] shorten __aeabi_memset by one instruction Em 21/04/2021 14:38, Rich Felker escreveu: > On Wed, Apr 21, 2021 at 10:24:58AM +0200, Szabolcs Nagy wrote: >> * Érico Nogueira [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) > > Should we hold off on doing anything about this for now then? I'd > rather avoid making more work for future, and this is pure *junk* code > that we do not expect to be called from anywhere (it's extremely slow) > and only there to satisfy broken tooling generating calls to it rather > than to the standard functions. That's ok for me. I was just browsing this file for some reason and noted the potential to "simplify" it. That said, src/string/arm/memcpy.S also uses this addressing mode, so it is probably relevant to watch out for it for an eventual port: /* align source to 32 bits. We need to insert 2 instructions between * a ldr[b|h] and str[b|h] because byte and half-word instructions * stall 2 cycles. */ movs r12, r3, lsl #31 sub r2, r2, r3 /* we know that r3 <= r2 because r2 >= 4 */ ldrbmi r3, [r1], #1 ldrbcs r4, [r1], #1 ldrbcs r12,[r1], #1 strbmi r3, [r0], #1 strbcs r4, [r0], #1 strbcs r12,[r0], #1 > > Rich