Add macro for the reserved error code

The documentation in error.h mentions that the error code -1 is reserved
for other errors. Make this explicit by adding a macro to error.h.

Author: yanesca

include/mbedtls/error.h

@@ -55,6 +55,7 @@
  * Low-level module errors (0x0002-0x007E, 0x0003-0x007F)
  *
  * Module   Nr  Codes assigned
+ * (any)     1                  0x0001
  * MPI       7  0x0002-0x0010
  * GCM       3  0x0012-0x0014   0x0013-0x0013
  * BLOWFISH  3  0x0016-0x0018   0x0017-0x0017
@@ -108,6 +109,8 @@
  * Module dependent error code (5 bits 0x.00.-0x.F8.)
  */
 
+#define MBEDTLS_ERR_GENERIC_ERROR       -0x0001  /**< Generic error */
+
 #ifdef __cplusplus
 extern "C" {
 #endif

library/error.c

@@ -688,6 +688,8 @@ void mbedtls_strerror( int ret, char *buf, size_t buflen )
     if( use_ret == -(MBEDTLS_ERR_XTEA_HW_ACCEL_FAILED) )
         mbedtls_snprintf( buf, buflen, "XTEA - XTEA hardware accelerator failed" );
 #endif /* MBEDTLS_XTEA_C */
+    if( use_ret == -(MBEDTLS_ERR_GENERIC_ERROR) )
+        mbedtls_snprintf( buf, buflen, "Generic error" );
     // END generated code
 
     if( strlen( buf ) != 0 )

scripts/generate_errors.pl

@@ -66,6 +66,9 @@
 
 my %error_codes_seen;
 
+my $reserved_name = "";
+my $reserved_description = "";
+my $ll_white_space = '    ';
 
 foreach my $line (@matches)
 {
@@ -82,6 +85,13 @@
         warn "Missing description for $error_name\n";
     }
 
+    if (hex($error_code) == 1)
+    {
+        $reserved_name = $error_name;
+        $reserved_description = $description;
+        next;
+    }
+
     my ($module_name) = $error_name =~ /^MBEDTLS_ERR_([^_]+)/;
 
     # Fix faulty ones
@@ -114,7 +124,7 @@
     {
         $code_check = \$ll_code_check;
         $old_define = \$ll_old_define;
-        $white_space = '    ';
+        $white_space = $ll_white_space;
     }
     else
     {
@@ -182,6 +192,13 @@
     $hl_code_check .= " */\n";
 }
 
+if ($reserved_name ne "")
+{
+    $ll_code_check .= "${ll_white_space}if( use_ret == -($reserved_name) )\n".
+                      "${ll_white_space}    mbedtls_snprintf( buf, buflen, \"".
+                      "$reserved_description\" );\n"
+}
+
 $error_format =~ s/HEADER_INCLUDED\n/$headers/g;
 $error_format =~ s/LOW_LEVEL_CODE_CHECKS\n/$ll_code_check/g;
 $error_format =~ s/HIGH_LEVEL_CODE_CHECKS\n/$hl_code_check/g;