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}
121