From d4da6f84e2e8bc550868a918ce9087a7bc4de224 Mon Sep 17 00:00:00 2001
From: Kareem <kareem@wolfssl.com>
Date: Wed, 15 May 2024 11:45:30 -0700
Subject: [PATCH] Avoid flexible arrays on unsupported platforms via a macro.

---
 src/dtls.c                  | 2 +-
 wolfssl/internal.h          | 6 +++---
 wolfssl/wolfcrypt/wc_port.h | 9 +++++++++
 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/dtls.c b/src/dtls.c
index ba7760dc94..43cf61f775 100644
--- a/src/dtls.c
+++ b/src/dtls.c
@@ -1040,7 +1040,7 @@ typedef struct ConnectionID {
 #ifdef _MSC_VER
 #pragma warning(disable: 4200)
 #endif
-    byte id[];
+    byte id[WOLFSSL_FLEXIBLE_ARRAY_SIZE];
 } ConnectionID;
 
 typedef struct CIDInfo {
diff --git a/wolfssl/internal.h b/wolfssl/internal.h
index c2d412986a..3b41b9c98a 100644
--- a/wolfssl/internal.h
+++ b/wolfssl/internal.h
@@ -3175,7 +3175,7 @@ typedef struct SignatureAlgorithms {
     #ifdef _MSC_VER
     #pragma warning(disable: 4200)
     #endif
-    byte        hashSigAlgo[]; /* sig/algo to offer */
+    byte        hashSigAlgo[WOLFSSL_FLEXIBLE_ARRAY_SIZE]; /* sig/algo to offer */
 } SignatureAlgorithms;
 
 WOLFSSL_LOCAL SignatureAlgorithms* TLSX_SignatureAlgorithms_New(
@@ -3353,7 +3353,7 @@ typedef struct Cookie {
     #ifdef _MSC_VER
     #pragma warning(disable: 4200)
     #endif
-    byte   data[];
+    byte   data[WOLFSSL_FLEXIBLE_ARRAY_SIZE];
 } Cookie;
 
 WOLFSSL_LOCAL int TLSX_Cookie_Use(const WOLFSSL* ssl, const byte* data,
@@ -5213,7 +5213,7 @@ typedef struct DtlsFragBucket {
 #ifdef _MSC_VER
 #pragma warning(disable: 4200)
 #endif
-    byte buf[];
+    byte buf[WOLFSSL_FLEXIBLE_ARRAY_SIZE];
 } DtlsFragBucket;
 
 typedef struct DtlsMsg {
diff --git a/wolfssl/wolfcrypt/wc_port.h b/wolfssl/wolfcrypt/wc_port.h
index 878e31913f..4cc62accb0 100644
--- a/wolfssl/wolfcrypt/wc_port.h
+++ b/wolfssl/wolfcrypt/wc_port.h
@@ -1267,6 +1267,15 @@ WOLFSSL_ABI WOLFSSL_API int wolfCrypt_Cleanup(void);
         #endif
     #endif
 
+#if defined(__STRICT_ANSI__)
+    #define WOLFSSL_FLEXIBLE_ARRAY_SIZE 1
+#elif defined(__GNUC__) && !defined(__clang__)
+    #define WOLFSSL_FLEXIBLE_ARRAY_SIZE
+    /*!< \brief Value appropriate as a size for an array that will be allocated to a variable size.  Built-in value usually works. */
+#else
+    #define WOLFSSL_FLEXIBLE_ARRAY_SIZE 0
+#endif
+
 #ifdef __cplusplus
     }  /* extern "C" */
 #endif