string_utils: provide a version of strchrnul() in case it's not available

This should only happen on Android.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

diff --git a/configure.ac b/configure.ac
index 9bd625a71f18263fb974110e7778a10adaa3bbb9..7c7b348726fd1ca2c5a2b5c0b18dde8c2d59839d 100644 (file)
--- 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 <linux/types.h>]])
 AC_CHECK_TYPES([struct open_how], [], [], [[#include <linux/openat2.h>]])
 AC_CHECK_TYPES([struct clone_args], [], [], [[#include <linux/sched.h>]])

diff --git a/src/include/stchrnul.c b/src/include/stchrnul.c
new file mode 100644 (file)
index 0000000..df3d5e2
--- /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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <string.h>
+#include <stdlib.h>
+
+/* 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 (file)
index 0000000..70a0d94
--- /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
+   <https://www.gnu.org/licenses/>.  */
+
+#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 52e3f35d5ea63863a74be860fc8cf5bd39f19bda..688587de155c4f5ff986d9daf68881fcbff4a378 100644 (file)
--- 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);