1 // Copyright (c) 2006-2009 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #include "build/build_config.h" 6 #include "base/safe_strerror_posix.h" 7 8 #include <errno.h> 9 #include <stdio.h> 10 #include <string.h> 11 12 #define USE_HISTORICAL_STRERRO_R (defined(__GLIBC__) || defined(OS_NACL)) 13 14 #if USE_HISTORICAL_STRERRO_R && defined(__GNUC__) 15 // GCC will complain about the unused second wrap function unless we tell it 16 // that we meant for them to be potentially unused, which is exactly what this 17 // attribute is for. 18 #define POSSIBLY_UNUSED __attribute__((unused)) 19 #else 20 #define POSSIBLY_UNUSED 21 #endif 22 23 #if USE_HISTORICAL_STRERRO_R 24 // glibc has two strerror_r functions: a historical GNU-specific one that 25 // returns type char *, and a POSIX.1-2001 compliant one available since 2.3.4 26 // that returns int. This wraps the GNU-specific one. 27 static void POSSIBLY_UNUSED wrap_posix_strerror_r( 28 char *(*strerror_r_ptr)(int, char *, size_t), 29 int err, 30 char *buf, 31 size_t len) { 32 // GNU version. 33 char *rc = (*strerror_r_ptr)(err, buf, len); 34 if (rc != buf) { 35 // glibc did not use buf and returned a static string instead. Copy it 36 // into buf. 37 buf[0] = '\0'; 38 strncat(buf, rc, len - 1); 39 } 40 // The GNU version never fails. Unknown errors get an "unknown error" message. 41 // The result is always null terminated. 42 } 43 #endif // USE_HISTORICAL_STRERRO_R 44 45 // Wrapper for strerror_r functions that implement the POSIX interface. POSIX 46 // does not define the behaviour for some of the edge cases, so we wrap it to 47 // guarantee that they are handled. This is compiled on all POSIX platforms, but 48 // it will only be used on Linux if the POSIX strerror_r implementation is 49 // being used (see below). 50 static void POSSIBLY_UNUSED wrap_posix_strerror_r( 51 int (*strerror_r_ptr)(int, char *, size_t), 52 int err, 53 char *buf, 54 size_t len) { 55 int old_errno = errno; 56 // Have to cast since otherwise we get an error if this is the GNU version 57 // (but in such a scenario this function is never called). Sadly we can't use 58 // C++-style casts because the appropriate one is reinterpret_cast but it's 59 // considered illegal to reinterpret_cast a type to itself, so we get an 60 // error in the opposite case. 61 int result = (*strerror_r_ptr)(err, buf, len); 62 if (result == 0) { 63 // POSIX is vague about whether the string will be terminated, although 64 // it indirectly implies that typically ERANGE will be returned, instead 65 // of truncating the string. We play it safe by always terminating the 66 // string explicitly. 67 buf[len - 1] = '\0'; 68 } else { 69 // Error. POSIX is vague about whether the return value is itself a system 70 // error code or something else. On Linux currently it is -1 and errno is 71 // set. On BSD-derived systems it is a system error and errno is unchanged. 72 // We try and detect which case it is so as to put as much useful info as 73 // we can into our message. 74 int strerror_error; // The error encountered in strerror 75 int new_errno = errno; 76 if (new_errno != old_errno) { 77 // errno was changed, so probably the return value is just -1 or something 78 // else that doesn't provide any info, and errno is the error. 79 strerror_error = new_errno; 80 } else { 81 // Either the error from strerror_r was the same as the previous value, or 82 // errno wasn't used. Assume the latter. 83 strerror_error = result; 84 } 85 // snprintf truncates and always null-terminates. 86 snprintf(buf, 87 len, 88 "Error %d while retrieving error %d", 89 strerror_error, 90 err); 91 } 92 errno = old_errno; 93 } 94 95 void safe_strerror_r(int err, char *buf, size_t len) { 96 if (buf == NULL || len <= 0) { 97 return; 98 } 99 // If using glibc (i.e., Linux), the compiler will automatically select the 100 // appropriate overloaded function based on the function type of strerror_r. 101 // The other one will be elided from the translation unit since both are 102 // static. 103 wrap_posix_strerror_r(&strerror_r, err, buf, len); 104 } 105 106 std::string safe_strerror(int err) { 107 const int buffer_size = 256; 108 char buf[buffer_size]; 109 safe_strerror_r(err, buf, sizeof(buf)); 110 return std::string(buf); 111 } 112
