sysdeps/unix/sysv/linux/dl-sysdep.c

   1 /* Dynamic linker system dependencies for Linux.
   2    Copyright (C) 1995,1997,2001,2004,2005,2006, 2008 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 /* Linux needs some special initialization, but otherwise uses
  20    the generic dynamic linker system interface code.  */
  21
  22 #include <string.h>
  23 #include <fcntl.h>
  24 #include <unistd.h>
  25 #include <sys/utsname.h>
  26 #include <ldsodefs.h>
  27 #include <kernel-features.h>
  28
  29 #ifdef SHARED
  30 # define DL_SYSDEP_INIT frob_brk ()
  31
  32 static inline void
  33 frob_brk (void)
  34 {
  35   __brk (0);                    /* Initialize the break.  */
  36
  37 #if ! __ASSUME_BRK_PAGE_ROUNDED
  38   /* If the dynamic linker was executed as a program, then the break may
  39      start immediately after our data segment.  However, dl-minimal.c has
  40      already stolen the remainder of the page for internal allocations.
  41      If we don't adjust the break location recorded by the kernel, the
  42      normal program startup will inquire, find the value at our &_end,
  43      and start allocating its own data there, clobbering dynamic linker
  44      data structures allocated there during startup.
  45
  46      Later Linux kernels have changed this behavior so that the initial
  47      break value is rounded up to the page boundary before we start.  */
  48
  49   extern char *__curbrk attribute_hidden;
  50   extern char _end[] attribute_hidden;
  51   char *const endpage = (void *) 0 + (((__curbrk - (char *) 0)
  52                                        + GLRO(dl_pagesize) - 1)
  53                                       & -GLRO(dl_pagesize));
  54   if (__builtin_expect (__curbrk >= _end && __curbrk < endpage, 0))
  55     __brk (endpage);
  56 #endif
  57 }
  58
  59 # include <elf/dl-sysdep.c>
  60 #endif
  61
  62
  63 int
  64 attribute_hidden
  65 _dl_discover_osversion (void)
  66 {
  67 #if (defined NEED_DL_SYSINFO || defined NEED_DL_SYSINFO_DSO) && defined SHARED
  68   if (GLRO(dl_sysinfo_map) != NULL)
  69     {
  70       /* If the kernel-supplied DSO contains a note indicating the kernel's
  71          version, we don't need to call uname or parse any strings.  */
  72
  73       static const struct
  74       {
  75         ElfW(Nhdr) hdr;
  76         char vendor[8];
  77       } expected_note = { { sizeof "Linux", sizeof (ElfW(Word)), 0 }, "Linux" };
  78       const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
  79       const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
  80       for (uint_fast16_t i = 0; i < phnum; ++i)
  81         if (phdr[i].p_type == PT_NOTE)
  82           {
  83             const ElfW(Addr) start = (phdr[i].p_vaddr
  84                                       + GLRO(dl_sysinfo_map)->l_addr);
  85             const ElfW(Nhdr) *note = (const void *) start;
  86             while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
  87               {
  88                 if (!memcmp (note, &expected_note, sizeof expected_note))
  89                   return *(const ElfW(Word) *) ((const void *) note
  90                                                 + sizeof expected_note);
  91 #define ROUND(len) (((len) + sizeof note->n_type - 1) & -sizeof note->n_type)
  92                 note = ((const void *) (note + 1)
  93                         + ROUND (note->n_namesz) + ROUND (note->n_descsz));
  94 #undef ROUND
  95               }
  96           }
  97     }
  98 #endif
  99
 100   char bufmem[64];
 101   char *buf = bufmem;
 102   unsigned int version;
 103   int parts;
 104   char *cp;
 105   struct utsname uts;
 106
 107   /* Try the uname system call.  */
 108   if (__uname (&uts))
 109     {
 110       /* This was not successful.  Now try reading the /proc filesystem.  */
 111       int fd = __open ("/proc/sys/kernel/osrelease", O_RDONLY);
 112       if (fd < 0)
 113         return -1;
 114       ssize_t reslen = __read (fd, bufmem, sizeof (bufmem));
 115       __close (fd);
 116       if (reslen <= 0)
 117         /* This also didn't work.  We give up since we cannot
 118            make sure the library can actually work.  */
 119         return -1;
 120       buf[MIN (reslen, (ssize_t) sizeof (bufmem) - 1)] = '\0';
 121     }
 122   else
 123     buf = uts.release;
 124
 125   /* Now convert it into a number.  The string consists of at most
 126      three parts.  */
 127   version = 0;
 128   parts = 0;
 129   cp = buf;
 130   while ((*cp >= '0') && (*cp <= '9'))
 131     {
 132       unsigned int here = *cp++ - '0';
 133
 134       while ((*cp >= '0') && (*cp <= '9'))
 135         {
 136           here *= 10;
 137           here += *cp++ - '0';
 138         }
 139
 140       ++parts;
 141       version <<= 8;
 142       version |= here;
 143
 144       if (*cp++ != '.' || parts == 3)
 145         /* Another part following?  */
 146         break;
 147     }
 148
 149   if (parts < 3)
 150     version <<= 8 * (3 - parts);
 151
 152   return version;
 153 }