lib/mbedtls_errors: Add code to patch mbedtls for shortened error strs.

The file `mbedtls_errors/mp_mbedtls_errors.c` can be used instead of
`mbedtls/library/error.c` to give shorter error strings, reducing the build
size of the error strings from about 12-16kB down to about 2-5kB.

1 files changed, 165 insertions, 0 deletions

diff --git a/lib/mbedtls_errors/error.fmt b/lib/mbedtls_errors/error.fmt
new file mode 100644
index 000000000..5beeb6e7c
--- /dev/null
+++ b/lib/mbedtls_errors/error.fmt
@@ -0,0 +1,165 @@
+/*
+ *  Error message information
+ *
+ *  Copyright (C) 2006-2015, ARM Limited, All Rights Reserved
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+#if !defined(MBEDTLS_CONFIG_FILE)
+#include "mbedtls/config.h"
+#else
+#include MBEDTLS_CONFIG_FILE
+#endif
+
+#if defined(MBEDTLS_ERROR_C) || defined(MBEDTLS_ERROR_STRERROR_DUMMY)
+#include "mbedtls/error.h"
+#include <string.h>
+#endif
+
+#if defined(MBEDTLS_PLATFORM_C)
+#include "mbedtls/platform.h"
+#else
+#define mbedtls_snprintf snprintf
+#define mbedtls_time_t   time_t
+#endif
+
+#if defined(MBEDTLS_ERROR_C)
+
+#include <stdio.h>
+
+HEADER_INCLUDED
+
+// Error code table type
+struct ssl_errs {
+    int16_t errnum;
+    const char *errstr;
+};
+
+// Table of high level error codes
+static const struct ssl_errs mbedtls_high_level_error_tab[] = {
+// BEGIN generated code
+HIGH_LEVEL_CODE_CHECKS
+// END generated code
+};
+
+static const struct ssl_errs mbedtls_low_level_error_tab[] = {
+// Low level error codes
+//
+// BEGIN generated code
+LOW_LEVEL_CODE_CHECKS
+// END generated code
+};
+
+static const char *mbedtls_err_prefix = "MBEDTLS_ERR_";
+#define MBEDTLS_ERR_PREFIX_LEN ( sizeof("MBEDTLS_ERR_")-1 )
+
+// copy error text into buffer, ensure null termination, return strlen of result
+static size_t mbedtls_err_to_str(int err, const struct ssl_errs tab[], int tab_len, char *buf, size_t buflen) {
+    if (buflen == 0) return 0;
+
+    // prefix for all error names
+    strncpy(buf, mbedtls_err_prefix, buflen);
+    if (buflen <= MBEDTLS_ERR_PREFIX_LEN+1) {
+        buf[buflen-1] = 0;
+        return buflen-1;
+    }
+
+    // append error name from table
+    for (int i = 0; i < tab_len; i++) {
+        if (tab[i].errnum == err) {
+            strncpy(buf+MBEDTLS_ERR_PREFIX_LEN, tab[i].errstr, buflen-MBEDTLS_ERR_PREFIX_LEN);
+            buf[buflen-1] = 0;
+            return strlen(buf);
+        }
+    }
+
+    mbedtls_snprintf(buf+MBEDTLS_ERR_PREFIX_LEN, buflen-MBEDTLS_ERR_PREFIX_LEN, "UNKNOWN (0x%04X)",
+            err);
+    return strlen(buf);
+}
+
+#define ARRAY_SIZE(a) (sizeof(a) / sizeof((a)[0]))
+
+void mbedtls_strerror(int ret, char *buf, size_t buflen) {
+    int use_ret;
+
+    if (buflen == 0) return;
+
+    buf[buflen-1] = 0;
+
+    if (ret < 0) ret = -ret;
+
+    //
+    // High-level error codes
+    //
+    uint8_t got_hl = (ret & 0xFF80) != 0;
+    if (got_hl) {
+        use_ret = ret & 0xFF80;
+
+        // special case
+#if defined(MBEDTLS_SSL_TLS_C)
+        if (use_ret == -(MBEDTLS_ERR_SSL_FATAL_ALERT_MESSAGE)) {
+            strncpy(buf, "MBEDTLS_ERR_SSL_FATAL_ALERT_MESSAGE", buflen);
+            buf[buflen-1] = 0;
+            return;
+        }
+#endif
+
+        size_t len = mbedtls_err_to_str(use_ret, mbedtls_high_level_error_tab,
+                ARRAY_SIZE(mbedtls_high_level_error_tab), buf, buflen);
+
+        buf += len;
+        buflen -= len;
+        if (buflen == 0) return;
+    }
+
+    //
+    // Low-level error codes
+    //
+    use_ret = ret & ~0xFF80;
+
+    if (use_ret == 0) return;
+
+    // If high level code is present, make a concatenation between both error strings.
+    if (got_hl) {
+        if (buflen < 2) return;
+        *buf++ = '+';
+        buflen--;
+    }
+
+    mbedtls_err_to_str(use_ret, mbedtls_low_level_error_tab,
+            ARRAY_SIZE(mbedtls_low_level_error_tab), buf, buflen);
+}
+
+#else /* MBEDTLS_ERROR_C */
+
+#if defined(MBEDTLS_ERROR_STRERROR_DUMMY)
+
+/*
+ * Provide an non-function in case MBEDTLS_ERROR_C is not defined
+ */
+void mbedtls_strerror( int ret, char *buf, size_t buflen )
+{
+    ((void) ret);
+
+    if( buflen > 0 )
+        buf[0] = '\0';
+}
+
+#endif /* MBEDTLS_ERROR_STRERROR_DUMMY */
+
+#endif /* MBEDTLS_ERROR_C */