From 194ed4e6e66cab28c3b5c0226cdfe6cc382d1f5a Mon Sep 17 00:00:00 2001
From: Maria Matejka <mq@ucw.cz>
Date: Fri, 24 Nov 2023 12:11:21 +0100
Subject: [PATCH] Macro SKIP_BACK now evaluates its argument only once.

---
 lib/birdlib.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/birdlib.h b/lib/birdlib.h
index 9e60da39..9004704c 100644
--- a/lib/birdlib.h
+++ b/lib/birdlib.h
@@ -26,7 +26,11 @@
 #define OFFSETOF(s, i) ((size_t) &((s *)0)->i)
 #endif
 
-#define SKIP_BACK(s, i, p) ({ s *_ptr = ((s *)((char *)p - OFFSETOF(s, i))); SAME_TYPE(&_ptr->i, p); _ptr; })
+#define SKIP_BACK(s, i, p) ({ \
+    typeof(p) _orig = p; \
+    s *_ptr = ((s *)((char *)_orig - OFFSETOF(s, i))); \
+    SAME_TYPE(&_ptr->i, _orig); \
+    _ptr; })
 #define BIRD_ALIGN(s, a) (((s)+a-1)&~(a-1))
 #define CPU_STRUCT_ALIGN  (MAX_(_Alignof(void*), _Alignof(u64)))
 #define BIRD_CPU_ALIGN(s) BIRD_ALIGN((s), CPU_STRUCT_ALIGN)