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 #if defined(__ANDROID__)
6 // Post-L versions of bionic define the GNU-specific strerror_r if _GNU_SOURCE
7 // is defined, but the symbol is renamed to __gnu_strerror_r which only exists
8 // on those later versions. To preserve ABI compatibility with older versions,
9 // undefine _GNU_SOURCE and use the POSIX version.
10 #undef _GNU_SOURCE
11 #endif
12
13 #include "base/posix/safe_strerror.h"
14
15 #include <errno.h>
16 #include <stdio.h>
17 #include <string.h>
18
19 #include "build/build_config.h"
20
21 namespace base {
22
23 #if defined(__GLIBC__) || defined(OS_NACL)
24 #define USE_HISTORICAL_STRERRO_R 1
25 #else
26 #define USE_HISTORICAL_STRERRO_R 0
27 #endif
28
29 #if USE_HISTORICAL_STRERRO_R && defined(__GNUC__)
30 // GCC will complain about the unused second wrap function unless we tell it
31 // that we meant for them to be potentially unused, which is exactly what this
32 // attribute is for.
33 #define POSSIBLY_UNUSED __attribute__((unused))
34 #else
35 #define POSSIBLY_UNUSED
36 #endif
37
38 #if USE_HISTORICAL_STRERRO_R
39 // glibc has two strerror_r functions: a historical GNU-specific one that
40 // returns type char *, and a POSIX.1-2001 compliant one available since 2.3.4
41 // that returns int. This wraps the GNU-specific one.
wrap_posix_strerror_r(char * (* strerror_r_ptr)(int,char *,size_t),int err,char * buf,size_t len)42 static void POSSIBLY_UNUSED wrap_posix_strerror_r(
43 char *(*strerror_r_ptr)(int, char *, size_t),
44 int err,
45 char *buf,
46 size_t len) {
47 // GNU version.
48 char *rc = (*strerror_r_ptr)(err, buf, len);
49 if (rc != buf) {
50 // glibc did not use buf and returned a static string instead. Copy it
51 // into buf.
52 buf[0] = '\0';
53 strncat(buf, rc, len - 1);
54 }
55 // The GNU version never fails. Unknown errors get an "unknown error" message.
56 // The result is always null terminated.
57 }
58 #endif // USE_HISTORICAL_STRERRO_R
59
60 // Wrapper for strerror_r functions that implement the POSIX interface. POSIX
61 // does not define the behaviour for some of the edge cases, so we wrap it to
62 // guarantee that they are handled. This is compiled on all POSIX platforms, but
63 // it will only be used on Linux if the POSIX strerror_r implementation is
64 // being used (see below).
wrap_posix_strerror_r(int (* strerror_r_ptr)(int,char *,size_t),int err,char * buf,size_t len)65 static void POSSIBLY_UNUSED wrap_posix_strerror_r(
66 int (*strerror_r_ptr)(int, char *, size_t),
67 int err,
68 char *buf,
69 size_t len) {
70 int old_errno = errno;
71 // Have to cast since otherwise we get an error if this is the GNU version
72 // (but in such a scenario this function is never called). Sadly we can't use
73 // C++-style casts because the appropriate one is reinterpret_cast but it's
74 // considered illegal to reinterpret_cast a type to itself, so we get an
75 // error in the opposite case.
76 int result = (*strerror_r_ptr)(err, buf, len);
77 if (result == 0) {
78 // POSIX is vague about whether the string will be terminated, although
79 // it indirectly implies that typically ERANGE will be returned, instead
80 // of truncating the string. We play it safe by always terminating the
81 // string explicitly.
82 buf[len - 1] = '\0';
83 } else {
84 // Error. POSIX is vague about whether the return value is itself a system
85 // error code or something else. On Linux currently it is -1 and errno is
86 // set. On BSD-derived systems it is a system error and errno is unchanged.
87 // We try and detect which case it is so as to put as much useful info as
88 // we can into our message.
89 int strerror_error; // The error encountered in strerror
90 int new_errno = errno;
91 if (new_errno != old_errno) {
92 // errno was changed, so probably the return value is just -1 or something
93 // else that doesn't provide any info, and errno is the error.
94 strerror_error = new_errno;
95 } else {
96 // Either the error from strerror_r was the same as the previous value, or
97 // errno wasn't used. Assume the latter.
98 strerror_error = result;
99 }
100 // snprintf truncates and always null-terminates.
101 snprintf(buf,
102 len,
103 "Error %d while retrieving error %d",
104 strerror_error,
105 err);
106 }
107 errno = old_errno;
108 }
109
safe_strerror_r(int err,char * buf,size_t len)110 void safe_strerror_r(int err, char *buf, size_t len) {
111 if (buf == nullptr || len <= 0) {
112 return;
113 }
114 // If using glibc (i.e., Linux), the compiler will automatically select the
115 // appropriate overloaded function based on the function type of strerror_r.
116 // The other one will be elided from the translation unit since both are
117 // static.
118 wrap_posix_strerror_r(&strerror_r, err, buf, len);
119 }
120
safe_strerror(int err)121 std::string safe_strerror(int err) {
122 const int buffer_size = 256;
123 char buf[buffer_size];
124 safe_strerror_r(err, buf, sizeof(buf));
125 return std::string(buf);
126 }
127
128 } // namespace base
129