From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yw1-x112a.google.com (mail-yw1-x112a.google.com [IPv6:2607:f8b0:4864:20::112a]) by sourceware.org (Postfix) with ESMTPS id 5AC9A3858D37 for ; Wed, 1 Feb 2023 19:39:49 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 5AC9A3858D37 Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-yw1-x112a.google.com with SMTP id 00721157ae682-4a263c4ddbaso261124217b3.0 for ; Wed, 01 Feb 2023 11:39:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=V9GZyUcjd/HUz8a2aWMyEcfUpHqgMr23vwd6BoGim6g=; b=DrLgOeipvZiDp+MqxToefQ5dqxgdXolBEg+hHqRrVFpojVmh1hpuChrzad7EM297nk Nh3Dat6rdC1JKnXobRjEgMFEBLNk78LAjH82RfI7/EcP0TPE7WS10/W3d+sE4GulQx3r qJRwPK6hdZS3HX6BZ/q1r9ZyAznCc6/P//Ry3rVV6W8Ug8HthX0E8BfgddMQ3DjuQS2Y XO0Gw5rfvxHdcsQInNJu5m6ZAmKHmCsHDZW8D9sZtmFG1d4WhS3JQlsJCTY4536BJMF5 JWkTdl5YNLQAP1MokZYVPS9HQjg/fYzNCX3UNqfEfj1juatQCCVmUAazclxhuD4m09Vz RnCA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=V9GZyUcjd/HUz8a2aWMyEcfUpHqgMr23vwd6BoGim6g=; b=N6rViDCrL5Go19xewGz7LEhbq7x+FN4PTL2OfiDHT38Ig4M5n/alX2GQWeLSEmu0fN iZ2UOAae8CijIhKyXs8JlYQekov7Tu0AfoiR2FiNF9I1S2T/D0ePcWuG9lX26O8pOoNY bvfiFdRGh3ObMMREY0iCIgI9/ZK1Y0I+2FnjAeu6bacd8Eese0CxAQlJfWxPGOqyrKek d7rhyWWJsu+jR97ri/ps2uJsfvJVzVwYdjNNxTxOzkMed7C6cmt38Zzra1BXB/vzXTBJ RPRt7OXuZs+DbalYoaFV4o7/lWXRyAhramCxVfvtj4boBznshpW7WUlBRlivJt9oEKm2 rpKw== X-Gm-Message-State: AO0yUKVYbYHVyIybEyxrqUH8ug/kNXRhasKpB+9Jpbh2t7x9F221fKIR smir24vYOrV/1+ihXnxZ4ZeDdwVMB2q+pL3v98E= X-Google-Smtp-Source: AK7set9gk4RmaHpwC5vmgaFjjQESGI177DMBvZ12HrIPO/l8FqSdvybN7VBpCmiT5dKq/xlvV1bV9RyCNwlKOiWU9p0= X-Received: by 2002:a81:46d4:0:b0:506:3d29:a280 with SMTP id t203-20020a8146d4000000b005063d29a280mr401381ywa.421.1675280387944; Wed, 01 Feb 2023 11:39:47 -0800 (PST) MIME-Version: 1.0 References: <20230201170406.303978-1-adhemerval.zanella@linaro.org> <20230201170406.303978-6-adhemerval.zanella@linaro.org> In-Reply-To: <20230201170406.303978-6-adhemerval.zanella@linaro.org> From: Noah Goldstein Date: Wed, 1 Feb 2023 13:39:35 -0600 Message-ID: Subject: Re: [PATCH v11 05/29] string: Improve generic strnlen with memchr To: Adhemerval Zanella Cc: libc-alpha@sourceware.org, Richard Henderson , Jeff Law , Xi Ruoyao Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-8.7 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,GIT_PATCH_0,KAM_SHORT,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On Wed, Feb 1, 2023 at 11:04 AM Adhemerval Zanella wrote: > > It also cleanups the multiple inclusion by leaving the ifunc > implementation to undef the weak_alias and libc_hidden_def. > > Co-authored-by: Richard Henderson > --- > string/strnlen.c | 137 +----------------- > sysdeps/i386/i686/multiarch/strnlen-c.c | 14 +- > .../power4/multiarch/strnlen-ppc32.c | 14 +- > sysdeps/s390/strnlen-c.c | 14 +- > 4 files changed, 27 insertions(+), 152 deletions(-) > > diff --git a/string/strnlen.c b/string/strnlen.c > index 6ff294eab1..dc23354ec8 100644 > --- a/string/strnlen.c > +++ b/string/strnlen.c > @@ -1,10 +1,6 @@ > /* Find the length of STRING, but scan at most MAXLEN characters. > Copyright (C) 1991-2023 Free Software Foundation, Inc. > > - Based on strlen written by Torbjorn Granlund (tege@sics.se), > - with help from Dan Sahlin (dan@sics.se); > - commentary by Jim Blandy (jimb@ai.mit.edu). > - > The GNU C Library is free software; you can redistribute it and/or > modify it under the terms of the GNU Lesser General Public License as > published by the Free Software Foundation; either version 2.1 of the > @@ -20,7 +16,6 @@ > not, see . */ > > #include > -#include > > /* Find the length of S, but scan at most MAXLEN characters. If no > '\0' terminator is found in that many characters, return MAXLEN. */ > @@ -32,134 +27,12 @@ > size_t > __strnlen (const char *str, size_t maxlen) > { > - const char *char_ptr, *end_ptr = str + maxlen; > - const unsigned long int *longword_ptr; > - unsigned long int longword, himagic, lomagic; > - > - if (maxlen == 0) > - return 0; > - > - if (__glibc_unlikely (end_ptr < str)) > - end_ptr = (const char *) ~0UL; > - > - /* Handle the first few characters by reading one character at a time. > - Do this until CHAR_PTR is aligned on a longword boundary. */ > - for (char_ptr = str; ((unsigned long int) char_ptr > - & (sizeof (longword) - 1)) != 0; > - ++char_ptr) > - if (*char_ptr == '\0') > - { > - if (char_ptr > end_ptr) > - char_ptr = end_ptr; > - return char_ptr - str; > - } > - > - /* All these elucidatory comments refer to 4-byte longwords, > - but the theory applies equally well to 8-byte longwords. */ > - > - longword_ptr = (unsigned long int *) char_ptr; > - > - /* Bits 31, 24, 16, and 8 of this number are zero. Call these bits > - the "holes." Note that there is a hole just to the left of > - each byte, with an extra at the end: > - > - bits: 01111110 11111110 11111110 11111111 > - bytes: AAAAAAAA BBBBBBBB CCCCCCCC DDDDDDDD > - > - The 1-bits make sure that carries propagate to the next 0-bit. > - The 0-bits provide holes for carries to fall into. */ > - himagic = 0x80808080L; > - lomagic = 0x01010101L; > - if (sizeof (longword) > 4) > - { > - /* 64-bit version of the magic. */ > - /* Do the shift in two steps to avoid a warning if long has 32 bits. */ > - himagic = ((himagic << 16) << 16) | himagic; > - lomagic = ((lomagic << 16) << 16) | lomagic; > - } > - if (sizeof (longword) > 8) > - abort (); > - > - /* Instead of the traditional loop which tests each character, > - we will test a longword at a time. The tricky part is testing > - if *any of the four* bytes in the longword in question are zero. */ > - while (longword_ptr < (unsigned long int *) end_ptr) > - { > - /* We tentatively exit the loop if adding MAGIC_BITS to > - LONGWORD fails to change any of the hole bits of LONGWORD. > - > - 1) Is this safe? Will it catch all the zero bytes? > - Suppose there is a byte with all zeros. Any carry bits > - propagating from its left will fall into the hole at its > - least significant bit and stop. Since there will be no > - carry from its most significant bit, the LSB of the > - byte to the left will be unchanged, and the zero will be > - detected. > - > - 2) Is this worthwhile? Will it ignore everything except > - zero bytes? Suppose every byte of LONGWORD has a bit set > - somewhere. There will be a carry into bit 8. If bit 8 > - is set, this will carry into bit 16. If bit 8 is clear, > - one of bits 9-15 must be set, so there will be a carry > - into bit 16. Similarly, there will be a carry into bit > - 24. If one of bits 24-30 is set, there will be a carry > - into bit 31, so all of the hole bits will be changed. > - > - The one misfire occurs when bits 24-30 are clear and bit > - 31 is set; in this case, the hole at bit 31 is not > - changed. If we had access to the processor carry flag, > - we could close this loophole by putting the fourth hole > - at bit 32! > - > - So it ignores everything except 128's, when they're aligned > - properly. */ > - > - longword = *longword_ptr++; > - > - if ((longword - lomagic) & himagic) > - { > - /* Which of the bytes was the zero? If none of them were, it was > - a misfire; continue the search. */ > - > - const char *cp = (const char *) (longword_ptr - 1); > - > - char_ptr = cp; > - if (cp[0] == 0) > - break; > - char_ptr = cp + 1; > - if (cp[1] == 0) > - break; > - char_ptr = cp + 2; > - if (cp[2] == 0) > - break; > - char_ptr = cp + 3; > - if (cp[3] == 0) > - break; > - if (sizeof (longword) > 4) > - { > - char_ptr = cp + 4; > - if (cp[4] == 0) > - break; > - char_ptr = cp + 5; > - if (cp[5] == 0) > - break; > - char_ptr = cp + 6; > - if (cp[6] == 0) > - break; > - char_ptr = cp + 7; > - if (cp[7] == 0) > - break; > - } > - } > - char_ptr = end_ptr; > - } > - > - if (char_ptr > end_ptr) > - char_ptr = end_ptr; > - return char_ptr - str; > + const char *found = memchr (str, '\0', maxlen); Can be __memchr to skip PLT no? > + return found ? found - str : maxlen; > } > + > #ifndef STRNLEN > -libc_hidden_def (__strnlen) > weak_alias (__strnlen, strnlen) > -#endif > +libc_hidden_def (__strnlen) > libc_hidden_def (strnlen) > +#endif > diff --git a/sysdeps/i386/i686/multiarch/strnlen-c.c b/sysdeps/i386/i686/multiarch/strnlen-c.c > index 351e939a93..beb0350d53 100644 > --- a/sysdeps/i386/i686/multiarch/strnlen-c.c > +++ b/sysdeps/i386/i686/multiarch/strnlen-c.c > @@ -1,10 +1,10 @@ > #define STRNLEN __strnlen_ia32 > +#include > + > #ifdef SHARED > -# undef libc_hidden_def > -# define libc_hidden_def(name) \ > - __hidden_ver1 (__strnlen_ia32, __GI_strnlen, __strnlen_ia32); \ > - strong_alias (__strnlen_ia32, __strnlen_ia32_1); \ > - __hidden_ver1 (__strnlen_ia32_1, __GI___strnlen, __strnlen_ia32_1); > +/* Alias for internal symbol to avoid PLT generation, it redirects the > + libc_hidden_def (__strnlen/strlen) to default implementation. */ > +__hidden_ver1 (__strnlen_ia32, __GI_strnlen, __strnlen_ia32); > +strong_alias (__strnlen_ia32, __strnlen_ia32_1); > +__hidden_ver1 (__strnlen_ia32_1, __GI___strnlen, __strnlen_ia32_1); > #endif > - > -#include "string/strnlen.c" > diff --git a/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c b/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c > index 957b9b99e8..2ca1cd7181 100644 > --- a/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c > +++ b/sysdeps/powerpc/powerpc32/power4/multiarch/strnlen-ppc32.c > @@ -17,12 +17,12 @@ > . */ > > #define STRNLEN __strnlen_ppc > +#include > + > #ifdef SHARED > -# undef libc_hidden_def > -# define libc_hidden_def(name) \ > - __hidden_ver1 (__strnlen_ppc, __GI_strnlen, __strnlen_ppc); \ > - strong_alias (__strnlen_ppc, __strnlen_ppc_1); \ > - __hidden_ver1 (__strnlen_ppc_1, __GI___strnlen, __strnlen_ppc_1); > +/* Alias for internal symbol to avoid PLT generation, it redirects the > + libc_hidden_def (__strnlen/strlen) to default implementation. */ > +__hidden_ver1 (__strnlen_ppc, __GI_strnlen, __strnlen_ppc); \ > +strong_alias (__strnlen_ppc, __strnlen_ppc_1); \ > +__hidden_ver1 (__strnlen_ppc_1, __GI___strnlen, __strnlen_ppc_1); > #endif > - > -#include > diff --git a/sysdeps/s390/strnlen-c.c b/sysdeps/s390/strnlen-c.c > index 172fcc7caa..95156a0ff5 100644 > --- a/sysdeps/s390/strnlen-c.c > +++ b/sysdeps/s390/strnlen-c.c > @@ -21,14 +21,16 @@ > #if HAVE_STRNLEN_C > # if HAVE_STRNLEN_IFUNC > # define STRNLEN STRNLEN_C > +# endif > + > +# include > + > +# if HAVE_STRNLEN_IFUNC > # if defined SHARED && IS_IN (libc) > -# undef libc_hidden_def > -# define libc_hidden_def(name) \ > - __hidden_ver1 (__strnlen_c, __GI_strnlen, __strnlen_c); \ > - strong_alias (__strnlen_c, __strnlen_c_1); \ > - __hidden_ver1 (__strnlen_c_1, __GI___strnlen, __strnlen_c_1); > +__hidden_ver1 (__strnlen_c, __GI_strnlen, __strnlen_c); > +strong_alias (__strnlen_c, __strnlen_c_1); > +__hidden_ver1 (__strnlen_c_1, __GI___strnlen, __strnlen_c_1); > # endif > # endif > > -# include > #endif > -- > 2.34.1 >