source/libs/libpng/libpng-1.6.16/contrib/arm-neon/linux-auxv.c

   1 /* contrib/arm-neon/linux-auxv.c
   2  *
   3  * Copyright (c) 2014 Glenn Randers-Pehrson
   4  * Written by Mans Rullgard, 2011.
   5  * Last changed in libpng 1.6.10 [March 6, 2014]
   6  *
   7  * This code is released under the libpng license.
   8  * For conditions of distribution and use, see the disclaimer
   9  * and license in png.h
  10  *
  11  * SEE contrib/arm-neon/README before reporting bugs
  12  *
  13  * STATUS: COMPILED, TESTED
  14  * BUG REPORTS: png-mng-implement@sourceforge.net
  15  *
  16  * png_have_neon implemented for Linux versions which allow access to
  17  * /proc/self/auxv.  This is probably faster, cleaner and safer than the code to
  18  * read /proc/cpuinfo in contrib/arm-neon/linux, however it is yet another piece
  19  * of potentially untested code and has more complex dependencies than the code
  20  * to read cpuinfo.
  21  *
  22  * This generic __linux__ implementation requires reading /proc/self/auxv and
  23  * looking at each element for one that records NEON capabilities.
  24  */
  25 #include <unistd.h> /* for POSIX 1003.1 */
  26 #include <errno.h>  /* for EINTR */
  27
  28 #include <sys/types.h>
  29 #include <sys/stat.h>
  30 #include <fcntl.h>
  31 #include <elf.h>
  32 #include <asm/hwcap.h>
  33
  34 /* A read call may be interrupted, in which case it returns -1 and sets errno to
  35  * EINTR if nothing was done, otherwise (if something was done) a partial read
  36  * may result.
  37  */
  38 static size_t
  39 safe_read(png_structp png_ptr, int fd, void *buffer_in, size_t nbytes)
  40 {
  41    size_t ntotal = 0;
  42    char *buffer = png_voidcast(char*, buffer_in);
  43
  44    while (nbytes > 0)
  45    {
  46       unsigned int nread;
  47       int iread;
  48
  49       /* Passing nread > INT_MAX to read is implementation defined in POSIX
  50        * 1003.1, therefore despite the unsigned argument portable code must
  51        * limit the value to INT_MAX!
  52        */
  53       if (nbytes > INT_MAX)
  54          nread = INT_MAX;
  55
  56       else
  57          nread = (unsigned int)/*SAFE*/nbytes;
  58
  59       iread = read(fd, buffer, nread);
  60
  61       if (iread == -1)
  62       {
  63          /* This is the devil in the details, a read can terminate early with 0
  64           * bytes read because of EINTR, yet it still returns -1 otherwise end
  65           * of file cannot be distinguished.
  66           */
  67          if (errno != EINTR)
  68          {
  69             png_warning(png_ptr, "/proc read failed");
  70             return 0; /* I.e., a permanent failure */
  71          }
  72       }
  73
  74       else if (iread < 0)
  75       {
  76          /* Not a valid 'read' result: */
  77          png_warning(png_ptr, "OS /proc read bug");
  78          return 0;
  79       }
  80
  81       else if (iread > 0)
  82       {
  83          /* Continue reading until a permanent failure, or EOF */
  84          buffer += iread;
  85          nbytes -= (unsigned int)/*SAFE*/iread;
  86          ntotal += (unsigned int)/*SAFE*/iread;
  87       }
  88
  89       else
  90          return ntotal;
  91    }
  92
  93    return ntotal; /* nbytes == 0 */
  94 }
  95
  96 static int
  97 png_have_neon(png_structp png_ptr)
  98 {
  99    int fd = open("/proc/self/auxv", O_RDONLY);
 100    Elf32_auxv_t aux;
 101
 102    /* Failsafe: failure to open means no NEON */
 103    if (fd == -1)
 104    {
 105       png_warning(png_ptr, "/proc/self/auxv open failed");
 106       return 0;
 107    }
 108
 109    while (safe_read(png_ptr, fd, &aux, sizeof aux) == sizeof aux)
 110    {
 111       if (aux.a_type == AT_HWCAP && (aux.a_un.a_val & HWCAP_NEON) != 0)
 112       {
 113          close(fd);
 114          return 1;
 115       }
 116    }
 117
 118    close(fd);
 119    return 0;
 120 }