support/errno.c

   1 /*
   2  * <errno.h> wrapper functions.
   3  */
   4
   5 #include <errno.h>
   6 #include <string.h>
   7 #include "map.h"
   8 #include "mph.h"
   9 #include <stdio.h>
  10
  11 G_BEGIN_DECLS
  12
  13 int
  14 Mono_Posix_Stdlib_GetLastError (void)
  15 {
  16         return errno;
  17 }
  18
  19 void
  20 Mono_Posix_Stdlib_SetLastError (int error_number)
  21 {
  22         errno = error_number;
  23 }
  24
  25 #ifdef HAVE_STRERROR_R
  26
  27 /*
  28  * There are two versions of strerror_r:
  29  *  - the GNU version:  char *strerror_r (int errnum, char *buf, size_t n);
  30  *  - the XPG version:    int strerror_r (int errnum, char *buf, size_t n);
  31  *
  32  * Ideally I could stick with the XPG version, but we need to support
  33  * Red Hat 9, which only supports the GNU version.
  34  *
  35  * Furthermore, I do NOT want to export the GNU version in Mono.Posix.dll,
  36  * as that's supposed to contain *standard* function definitions (give or
  37  * take a few GNU extensions).  Portability trumps all.
  38  *
  39  * Consequently, we export the functionality of the XPG version.
  40  * Internally, we se the GNU version if _GNU_SOURCE is defined, otherwise
  41  * we assume that the XPG version is present.
  42  */
  43
  44 #ifdef _GNU_SOURCE
  45 #define mph_min(x,y) ((x) <= (y) ? (x) : (y))
  46
  47 /* If you pass an invalid errno value to glibc 2.3.2's strerror_r, you get
  48  * back the string "Unknown error" with the error value appended. */
  49 static const char mph_unknown[] = "Unknown error ";
  50
  51 /*
  52  * Translate the GNU semantics to the XPG semantics.
  53  *
  54  * From reading the (RH9-using) GLibc 2.3.2 sysdeps/generic/_strerror.c,
  55  * we can say the following:
  56  *   - If errnum is a valid error number, a pointer to a constant string is
  57  *     returned.  Thus, the prototype *lies* (it's not really a char*).
  58  *     `buf' is unchanged (WTF?).
  59  *   - If errnum is an *invalid* error number, an error message is copied
  60  *     into `buf' and `buf' is returned.  The error message returned is
  61  *     "Unknown error %i", where %i is the input errnum.
  62  *
  63  * Meanwhile, XPG always modifies `buf' if there's enough space, and either
  64  * returns 0 (success) or -1 (error) with errno = EINVAL (bad errnum) or
  65  * ERANGE (`buf' isn't big enough).  Also, GLibc 2.3.3 (which has the XPG
  66  * version) first checks the validity of errnum first, then does the copy.
  67  *
  68  * Assuming that the GNU implementation doesn't change much (ha!), we can
  69  * check for EINVAL by comparing the strerror_r return to `buf', OR by
  70  * comparing the return value to "Uknown error".  (This assumes that
  71  * strerror_r will always only return the input buffer for errors.)
  72  *
  73  * Check for ERANGE by comparing the string length returned by strerror_r to
  74  * `n'.
  75  *
  76  * Then pray that this actually works...
  77  */
  78 gint32
  79 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
  80 {
  81         char *r;
  82         char ebuf [sizeof(mph_unknown)];
  83         size_t len;
  84         size_t blen;
  85
  86         mph_return_if_size_t_overflow (n);
  87
  88         /* first, check for valid errnum */
  89 #if PLATFORM_ANDROID
  90         /* Android NDK defines _GNU_SOURCE but strerror_r follows the XSI semantics
  91          * not the GNU one. XSI version returns an integer, as opposed to the GNU one
  92          * which returns pointer to the buffer.
  93          */
  94         if (strerror_r (errnum, ebuf, sizeof(ebuf)) == -1) {
  95                 /* XSI strerror_r will return -1 if errno is set, but if we leave the value
  96                  * alone it breaks Mono.Posix StdioFileStream tests, so we'll ignore the value
  97                  * and set errno as below
  98                  */
  99                 errno = EINVAL;
 100                 return -1;
 101         }
 102         r = ebuf;
 103 #else
 104         r = strerror_r (errnum, ebuf, sizeof(ebuf));
 105 #endif
 106         if (!r) {
 107                 errno = EINVAL;
 108                 return -1;
 109         }
 110         len = strlen (r);
 111
 112         if (r == ebuf ||
 113                         strncmp (r, mph_unknown, mph_min (len, sizeof(mph_unknown))) == 0) {
 114                 errno = EINVAL;
 115                 return -1;
 116         }
 117
 118         /* valid errnum (we hope); is buffer big enough? */
 119         blen = (size_t) n;
 120         if ((len+1) > blen) {
 121                 errno = ERANGE;
 122                 return -1;
 123         }
 124
 125         strncpy (buf, r, len);
 126         buf[len] = '\0';
 127
 128         return 0;
 129 }
 130
 131 #else /* !def _GNU_SOURCE */
 132
 133 gint32
 134 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
 135 {
 136         mph_return_if_size_t_overflow (n);
 137         return strerror_r (errnum, buf, (size_t) n);
 138 }
 139
 140 #endif /* def _GNU_SOURCE */
 141
 142 #endif /* def HAVE_STRERROR_R */
 143
 144 G_END_DECLS
 145
 146 /*
 147  * vim: noexpandtab
 148  */