Merge pull request #10318 from keith-packard/gcc-14-3-array-bounds

Avoid invalid gcc 14.3 warning about array bounds in mbedtls_xor

ChangeLog.d/gcc-14.3.txt

@@ -0,0 +1,4 @@
+Bugfix
+   * Appease GCC 14.3's array bounds checker by inserting checks in mbedtls_xor
+     that bail before the byte-at-a-time loop when the array size is a constant
+     (using MBEDTLS_HAS_BUILTIN) and an exact multiple of the larger loop size.

library/common.h

@@ -99,6 +99,13 @@ extern void (*mbedtls_test_hook_test_fail)(const char *test, int line, const cha
  * fall back to the unsafe implementation. */
 #define ARRAY_LENGTH(array) ARRAY_LENGTH_UNSAFE(array)
 #endif
+
+#if defined(__has_builtin)
+#define MBEDTLS_HAS_BUILTIN(x) __has_builtin(x)
+#else
+#define MBEDTLS_HAS_BUILTIN(x) 0
+#endif
+
 /** Allow library to access its structs' private members.
  *
  * Although structs defined in header files are publicly available,
@@ -208,6 +215,11 @@ static inline void mbedtls_xor(unsigned char *r,
         return;
     }
 #endif
+#if defined(MBEDTLS_COMPILER_IS_GCC) && MBEDTLS_HAS_BUILTIN(__builtin_constant_p)
+    if (__builtin_constant_p(n) && n % 16 == 0) {
+        return;
+    }
+#endif
 #elif defined(MBEDTLS_ARCH_IS_X64) || defined(MBEDTLS_ARCH_IS_ARM64)
     /* This codepath probably only makes sense on architectures with 64-bit registers */
     for (; (i + 8) <= n; i += 8) {
@@ -219,6 +231,11 @@ static inline void mbedtls_xor(unsigned char *r,
         return;
     }
 #endif
+#if defined(MBEDTLS_COMPILER_IS_GCC) && MBEDTLS_HAS_BUILTIN(__builtin_constant_p)
+    if (__builtin_constant_p(n) && n % 8 == 0) {
+        return;
+    }
+#endif
 #else
     for (; (i + 4) <= n; i += 4) {
         uint32_t x = mbedtls_get_unaligned_uint32(a + i) ^ mbedtls_get_unaligned_uint32(b + i);
@@ -229,6 +246,11 @@ static inline void mbedtls_xor(unsigned char *r,
         return;
     }
 #endif
+#if defined(MBEDTLS_COMPILER_IS_GCC) && MBEDTLS_HAS_BUILTIN(__builtin_constant_p)
+    if (__builtin_constant_p(n) && n % 4 == 0) {
+        return;
+    }
+#endif
 #endif
 #endif
     for (; i < n; i++) {
@@ -367,12 +389,6 @@ static inline void mbedtls_xor_no_simd(unsigned char *r,
     struct ISO_C_does_not_allow_extra_semicolon_outside_of_a_function
 #endif
 
-#if defined(__has_builtin)
-#define MBEDTLS_HAS_BUILTIN(x) __has_builtin(x)
-#else
-#define MBEDTLS_HAS_BUILTIN(x) 0
-#endif
-
 /* Define compiler branch hints */
 #if MBEDTLS_HAS_BUILTIN(__builtin_expect)
 #define MBEDTLS_LIKELY(x)       __builtin_expect(!!(x), 1)