Sireesh Tripurari | b478e66 | 2014-05-09 15:15:10 +0530 | [diff] [blame] | 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 | } |