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