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 */
 38static size_t
 39safe_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
 96static int
 97png_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}