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 (at) 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 } 121