From: Christian Brauner Date: Fri, 19 Mar 2021 14:19:07 +0000 (+0100) Subject: string_utils: provide a version of strchrnul() in case it's not available X-Git-Tag: lxc-5.0.0~254^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=88cf3229fe5dec0df3c560eb714c7365ba987f4d;p=thirdparty%2Flxc.git string_utils: provide a version of strchrnul() in case it's not available This should only happen on Android. Signed-off-by: Christian Brauner --- diff --git a/configure.ac b/configure.ac index 9bd625a71..7c7b34872 100644 --- a/configure.ac +++ b/configure.ac @@ -640,7 +640,7 @@ AC_CHECK_HEADER([ifaddrs.h], AC_HEADER_MAJOR # Check for some syscalls functions -AC_CHECK_FUNCS([setns pivot_root sethostname unshare rand_r confstr faccessat gettid memfd_create move_mount open_tree execveat clone3 fsopen fspick fsconfig fsmount, openat2, close_range, statvfs]) +AC_CHECK_FUNCS([setns pivot_root sethostname unshare rand_r confstr faccessat gettid memfd_create move_mount open_tree execveat clone3 fsopen fspick fsconfig fsmount, openat2, close_range, statvfs, strchrnul]) AC_CHECK_TYPES([__aligned_u64], [], [], [[#include ]]) AC_CHECK_TYPES([struct open_how], [], [], [[#include ]]) AC_CHECK_TYPES([struct clone_args], [], [], [[#include ]]) diff --git a/src/include/stchrnul.c b/src/include/stchrnul.c new file mode 100644 index 000000000..df3d5e2aa --- /dev/null +++ b/src/include/stchrnul.c @@ -0,0 +1,154 @@ +/* Copyright (C) 1991-2021 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Based on strlen implementation by Torbjorn Granlund (tege@sics.se), + with help from Dan Sahlin (dan@sics.se) and + bug fix and commentary by Jim Blandy (jimb@ai.mit.edu); + adaptation to strchr suggested by Dick Karpinski (dick@cca.ucsf.edu), + and implemented by Roland McGrath (roland@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 License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include +#include + +/* Find the first occurrence of C in S or the final NUL byte. */ +char *strchrnul(const char *s, int c_in) +{ + const unsigned char *char_ptr; + const unsigned long int *longword_ptr; + unsigned long int longword, magic_bits, charmask; + unsigned char c; + + c = (unsigned char)c_in; + + /* 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 = (const unsigned char *)s; + ((unsigned long int)char_ptr & (sizeof(longword) - 1)) != 0; + ++char_ptr) + if (*char_ptr == c || *char_ptr == '\0') + return (void *)char_ptr; + + /* 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. */ + magic_bits = -1; + magic_bits = magic_bits / 0xff * 0xfe << 1 >> 1 | 1; + + /* Set up a longword, each of whose bytes is C. */ + charmask = c | (c << 8); + charmask |= charmask << 16; + if (sizeof(longword) > 4) + /* Do the shift in two steps to avoid a warning if long has 32 bits. */ + charmask |= (charmask << 16) << 16; + 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. */ + for (;;) { + /* 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. + + 3) But wait! Aren't we looking for C as well as zero? + Good point. So what we do is XOR LONGWORD with a longword, + each of whose bytes is C. This turns each byte that is C + into a zero. */ + + longword = *longword_ptr++; + + /* Add MAGIC_BITS to LONGWORD. */ + if ((((longword + magic_bits) + + /* Set those bits that were unchanged by the addition. */ + ^ ~longword) + + /* Look at only the hole bits. If any of the hole bits + are unchanged, most likely one of the bytes was a + zero. */ + & ~magic_bits) != 0 + + /* That caught zeroes. Now test for C. */ + || ((((longword ^ charmask) + magic_bits) ^ + ~(longword ^ charmask)) & + ~magic_bits) != 0) { + /* Which of the bytes was C or zero? + If none of them were, it was a misfire; continue the search. */ + + const unsigned char *cp = + (const unsigned char *)(longword_ptr - 1); + + if (*cp == c || *cp == '\0') + return (char *)cp; + if (*++cp == c || *cp == '\0') + return (char *)cp; + if (*++cp == c || *cp == '\0') + return (char *)cp; + if (*++cp == c || *cp == '\0') + return (char *)cp; + if (sizeof(longword) > 4) { + if (*++cp == c || *cp == '\0') + return (char *)cp; + if (*++cp == c || *cp == '\0') + return (char *)cp; + if (*++cp == c || *cp == '\0') + return (char *)cp; + if (*++cp == c || *cp == '\0') + return (char *)cp; + } + } + } + + /* This should never happen. */ + return NULL; +} diff --git a/src/include/stchrnul.h b/src/include/stchrnul.h new file mode 100644 index 000000000..70a0d9442 --- /dev/null +++ b/src/include/stchrnul.h @@ -0,0 +1,25 @@ +/* Copyright (C) 1991-2021 Free Software Foundation, Inc. + This file is part of the GNU C Library. + Based on strlen implementation by Torbjorn Granlund (tege@sics.se), + with help from Dan Sahlin (dan@sics.se) and + bug fix and commentary by Jim Blandy (jimb@ai.mit.edu); + adaptation to strchr suggested by Dick Karpinski (dick@cca.ucsf.edu), + and implemented by Roland McGrath (roland@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 License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + . */ + +#include "compiler.h" + +__hidden extern char *strchrnul(const char *s, int c_in); diff --git a/src/lxc/string_utils.h b/src/lxc/string_utils.h index 52e3f35d5..688587de1 100644 --- a/src/lxc/string_utils.h +++ b/src/lxc/string_utils.h @@ -14,6 +14,10 @@ #include "include/strlcat.h" #endif +#ifndef HAVE_STRCHRNUL +#include "include/strchrnul.h" +#endif + /* convert variadic argument lists to arrays (for execl type argument lists) */ __hidden extern char **lxc_va_arg_list_to_argv(va_list ap, size_t skip, int do_strdup); __hidden extern const char **lxc_va_arg_list_to_argv_const(va_list ap, size_t skip);