* lib/obstack.in.h (_OBSTACK_CPTR): New macro.
(obstack_free): Use it instead of comparing pointers directly,
when the pointers might not point into the same object.
---
ChangeLog | 5 +++++
lib/obstack.in.h | 17 ++++++++++++++---
2 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/ChangeLog b/ChangeLog
index dc81c8c726..e63d92728a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
2025-05-07 Paul Eggert <egg...@cs.ucla.edu>
+ obstack: avoid undefined pointer comparison
+ * lib/obstack.in.h (_OBSTACK_CPTR): New macro.
+ (obstack_free): Use it instead of comparing pointers directly,
+ when the pointers might not point into the same object.
+
obstack: check def before use in macros
* lib/obstack.in.h (__attribute_noreturn__, __extension__):
Be more careful about checking whether a macro is defined before
diff --git a/lib/obstack.in.h b/lib/obstack.in.h
index 7d2327977e..4b133c32cc 100644
--- a/lib/obstack.in.h
+++ b/lib/obstack.in.h
@@ -136,6 +136,16 @@
# endif
#endif
+/* A type suitable for comparing pointers regardless of whether they
+ point into the same object, e.g., (_OBSTACK_CPTR) p < (_OBSTACK_CPTR) q.
+ If possible, use uintptr_t to avoid undefined behavior and pacify
+ sanitizers. Otherwise, use a pointer directly and hope for the best. */
+#ifdef _OBSTACK_UINTPTR_TYPE
+typedef _OBSTACK_UINTPTR_TYPE _OBSTACK_CPTR;
+#else
+typedef char *_OBSTACK_CPTR;
+#endif
+
/* These macros highlight the places where this implementation
is different from the one in GNU libc. */
#if defined __GL_GNULIB_HEADER
@@ -478,7 +488,8 @@ extern int obstack_exit_failure;
__extension__
\
({ struct obstack *__o = (OBSTACK);
\
void *__obj = (void *) (OBJ); \
- if (__obj > (void *) __o->chunk && __obj < (void *) __o->chunk_limit) \
+ if ((_OBSTACK_CPTR) __o->chunk < (_OBSTACK_CPTR) __obj \
+ && (_OBSTACK_CPTR) __obj < (_OBSTACK_CPTR) __o->chunk_limit)
\
__o->next_free = __o->object_base = (char *) __obj; \
else \
__obstack_free (__o, __obj); })
@@ -579,8 +590,8 @@ extern int obstack_exit_failure;
# define obstack_free(h, obj) \
((h)->temp.tempptr = (void *) (obj), \
- (((h)->temp.tempptr > (void *) (h)->chunk \
- && (h)->temp.tempptr < (void *) (h)->chunk_limit) \
+ (((_OBSTACK_CPTR) (h)->chunk < (OBSTACK_CPTR) (h)->temp.tempptr \
+ && (_OBSTACK_CPTR) (h)->temp.tempptr < (_OBSTACK_CPTR) (h)->chunk_limit) \
? (void) ((h)->next_free = (h)->object_base = (char *) (h)->temp.tempptr) \
: __obstack_free ((h), (h)->temp.tempptr)))
--
2.49.0
