The C standard specifies that it's undefined behavior to dereference
NULL (even if you use & right after). The hand-rolled offsetof idiom
&(((s*)NULL)->f) is thus technically undefined. This clutters the
output of UBSan and is simple to fix: just use the real offsetof when
it's available.
This patch also changes two instances of pointer arithmetic on void *
to use char * instead, again to avoid UB.
After this patch, HAProxy can run without crashing after building w/
clang-19 -fsanitize=undefined -fno-sanitize=function,alignment
---
include/haproxy/compiler.h | 4 ++--
include/haproxy/list.h | 2 +-
include/import/mt_list.h | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/haproxy/compiler.h b/include/haproxy/compiler.h
index 80d9be772..52aee39b9 100644
--- a/include/haproxy/compiler.h
+++ b/include/haproxy/compiler.h
@@ -350,7 +350,7 @@
* <type> which has its member <name> stored at address <ptr>.
*/
#ifndef container_of
-#define container_of(ptr, type, name) ((type *)(((void *)(ptr)) -
((long)&((type *)0)->name)))
+#define container_of(ptr, type, name) ((type *)(((char *)(ptr)) -
offsetof(type, name)))
#endif
/* returns a pointer to the structure of type <type> which has its member
<name>
@@ -359,7 +359,7 @@
#ifndef container_of_safe
#define container_of_safe(ptr, type, name) \
({ void *__p = (ptr); \
- __p ? (type *)(__p - ((long)&((type *)0)->name)) : (type *)0; \
+ __p ? (type *)((char *)__p - offsetof(type, name)) : (type *)0;
\
})
#endif
diff --git a/include/haproxy/list.h b/include/haproxy/list.h
index ff203147c..c2fcdfbc6 100644
--- a/include/haproxy/list.h
+++ b/include/haproxy/list.h
@@ -97,7 +97,7 @@
* since it's used only once.
* Example: LIST_ELEM(cur_node->args.next, struct node *, args)
*/
-#define LIST_ELEM(lh, pt, el) ((pt)(((const char *)(lh)) -
((size_t)&((pt)NULL)->el)))
+#define LIST_ELEM(lh, pt, el) ((pt)(((const char *)(lh)) -
offsetof(typeof(*(pt)NULL), el)))
/* checks if the list head <lh> is empty or not */
#define LIST_ISEMPTY(lh) ((lh)->n == (lh))
diff --git a/include/import/mt_list.h b/include/import/mt_list.h
index 9339d0e07..09526eb0b 100644
--- a/include/import/mt_list.h
+++ b/include/import/mt_list.h
@@ -87,7 +87,7 @@ struct mt_list {
*
* return MT_LIST_ELEM(cur_node->args.next, struct node *, args)
*/
-#define MT_LIST_ELEM(a, t, m) ((t)(size_t)(((size_t)(a)) -
((size_t)&((t)NULL)->m)))
+#define MT_LIST_ELEM(a, t, m) ((t)(size_t)(((size_t)(a)) -
offsetof(typeof(*(t)NULL), m)))
/* Returns a pointer of type <t> to a structure following the element which
--
2.50.1
