From 4089affd371e6d62dd8c1e57b344f8cc329005ea Mon Sep 17 00:00:00 2001
From: Khem Raj <raj.khem@gmail.com>
Date: Sat, 14 Jan 2023 23:11:08 -0800
Subject: [PATCH] Define alignof using _Alignof when using C11 or newer

WG14 N2350 made very clear that it is an UB having type definitions
within "offsetof" [1]. This patch enhances the implementation of macro
alignof_slot to use builtin "_Alignof" to avoid undefined behavior on
when using std=c11 or newer

clang 16+ has started to flag this [2]

Fixes build when using -std >= gnu11 and using clang16+

Older compilers gcc < 4.9 or clang < 8 has buggy _Alignof even though it
may support C11, exclude those compilers too

[1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
[2] https://reviews.llvm.org/D133574

Upstream-Status: Submitted [https://groups.google.com/g/opkg-devel/c/gjcQPZgT_jI]
Signed-off-by: Khem Raj <raj.khem@gmail.com>
---
 libopkg/md5.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/libopkg/md5.c b/libopkg/md5.c
index 981b9b8..ccb645e 100644
--- a/libopkg/md5.c
+++ b/libopkg/md5.c
@@ -237,7 +237,17 @@ void md5_process_bytes(const void *buffer, size_t len, struct md5_ctx *ctx)
     /* Process available complete blocks.  */
     if (len >= 64) {
 #if !_STRING_ARCH_unaligned
+/* GCC releases before GCC 4.9 had a bug in _Alignof.  See GCC bug 52023
+   <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52023>.
+   clang versions < 8.0.0 have the same bug.  */
+#if (!defined __STDC_VERSION__ || __STDC_VERSION__ < 201112 \
+     || (defined __GNUC__ && __GNUC__ < 4 + (__GNUC_MINOR__ < 9) \
+         && !defined __clang__) \
+     || (defined __clang__ && __clang_major__ < 8))
 #define alignof(type) offsetof (struct { char c; type x; }, x)
+#else
+#define alignof(type) _Alignof(type)
+#endif
 #define UNALIGNED_P(p) (((size_t) p) % alignof (uint32_t) != 0)
         if (UNALIGNED_P(buffer))
             while (len > 64) {
-- 
2.39.0