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