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, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 /* Linux needs some special initialization, but otherwise uses
  21    the generic dynamic linker system interface code.  */
  22
  23 #include <string.h>
  24 #include <fcntl.h>
  25 #include <unistd.h>
  26 #include <sys/utsname.h>
  27 #include <ldsodefs.h>
  28 #include <kernel-features.h>
  29
  30 #ifdef SHARED
  31 # define DL_SYSDEP_INIT frob_brk ()
  32
  33 static inline void
  34 frob_brk (void)
  35 {
  36   __brk (0);                    /* Initialize the break.  */
  37
  38 #if ! __ASSUME_BRK_PAGE_ROUNDED
  39   /* If the dynamic linker was executed as a program, then the break may
  40      start immediately after our data segment.  However, dl-minimal.c has
  41      already stolen the remainder of the page for internal allocations.
  42      If we don't adjust the break location recorded by the kernel, the
  43      normal program startup will inquire, find the value at our &_end,
  44      and start allocating its own data there, clobbering dynamic linker
  45      data structures allocated there during startup.
  46
  47      Later Linux kernels have changed this behavior so that the initial
  48      break value is rounded up to the page boundary before we start.  */
  49
  50   extern void *__curbrk attribute_hidden;
  51   extern void _end attribute_hidden;
  52   void *const endpage = (void *) 0 + (((__curbrk - (void *) 0)
  53                                        + GLRO(dl_pagesize) - 1)
  54                                       & -GLRO(dl_pagesize));
  55   if (__builtin_expect (__curbrk >= &_end && __curbrk < endpage, 0))
  56     __brk (endpage);
  57 #endif
  58 }
  59
  60 # include <elf/dl-sysdep.c>
  61 #endif
  62
  63
  64 int
  65 attribute_hidden
  66 _dl_discover_osversion (void)
  67 {
  68 #if (defined NEED_DL_SYSINFO || defined NEED_DL_SYSINFO_DSO) && defined SHARED
  69   if (GLRO(dl_sysinfo_map) != NULL)
  70     {
  71       /* If the kernel-supplied DSO contains a note indicating the kernel's
  72          version, we don't need to call uname or parse any strings.  */
  73
  74       static const struct
  75       {
  76         ElfW(Nhdr) hdr;
  77         char vendor[8];
  78       } expected_note = { { sizeof "Linux", sizeof (ElfW(Word)), 0 }, "Linux" };
  79       const ElfW(Phdr) *const phdr = GLRO(dl_sysinfo_map)->l_phdr;
  80       const ElfW(Word) phnum = GLRO(dl_sysinfo_map)->l_phnum;
  81       for (uint_fast16_t i = 0; i < phnum; ++i)
  82         if (phdr[i].p_type == PT_NOTE)
  83           {
  84             const ElfW(Addr) start = (phdr[i].p_vaddr
  85                                       + GLRO(dl_sysinfo_map)->l_addr);
  86             const ElfW(Nhdr) *note = (const void *) start;
  87             while ((ElfW(Addr)) (note + 1) - start < phdr[i].p_memsz)
  88               {
  89                 if (!memcmp (note, &expected_note, sizeof expected_note))
  90                   return *(const ElfW(Word) *) ((const void *) note
  91                                                 + sizeof expected_note);
  92 #define ROUND(len) (((len) + sizeof note->n_type - 1) & -sizeof note->n_type)
  93                 note = ((const void *) (note + 1)
  94                         + ROUND (note->n_namesz) + ROUND (note->n_descsz));
  95 #undef ROUND
  96               }
  97           }
  98     }
  99 #endif
 100
 101   char bufmem[64];
 102   char *buf = bufmem;
 103   unsigned int version;
 104   int parts;
 105   char *cp;
 106   struct utsname uts;
 107
 108   /* Try the uname system call.  */
 109   if (__uname (&uts))
 110     {
 111       /* This was not successful.  Now try reading the /proc filesystem.  */
 112       int fd = __open ("/proc/sys/kernel/osrelease", O_RDONLY);
 113       if (fd < 0)
 114         return -1;
 115       ssize_t reslen = __read (fd, bufmem, sizeof (bufmem));
 116       __close (fd);
 117       if (reslen <= 0)
 118         /* This also didn't work.  We give up since we cannot
 119            make sure the library can actually work.  */
 120         return -1;
 121       buf[MIN (reslen, (ssize_t) sizeof (bufmem) - 1)] = '\0';
 122     }
 123   else
 124     buf = uts.release;
 125
 126   /* Now convert it into a number.  The string consists of at most
 127      three parts.  */
 128   version = 0;
 129   parts = 0;
 130   cp = buf;
 131   while ((*cp >= '0') && (*cp <= '9'))
 132     {
 133       unsigned int here = *cp++ - '0';
 134
 135       while ((*cp >= '0') && (*cp <= '9'))
 136         {
 137           here *= 10;
 138           here += *cp++ - '0';
 139         }
 140
 141       ++parts;
 142       version <<= 8;
 143       version |= here;
 144
 145       if (*cp++ != '.' || parts == 3)
 146         /* Another part following?  */
 147         break;
 148     }
 149
 150   if (parts < 3)
 151     version <<= 8 * (3 - parts);
 152
 153   return version;
 154 }