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Re: [Bug-gnulib] obstack uses casts as lvalues
From: |
Paul Eggert |
Subject: |
Re: [Bug-gnulib] obstack uses casts as lvalues |
Date: |
21 Oct 2003 18:49:35 -0700 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.3 |
"Joseph S. Myers" <address@hidden> writes:
> If they are used, they can't ever have worked, but maybe they need to be
> removed.
They're documented in the glibc manual, so it may be a hassle to
remove them. For now let's keep them.
> I think that reinterpreting the bit pattern of p in this way as another
> type of pointer would break the type-based aliasing rules.
OK. I installed the following more-conservative change. It's more
elaborate than what you proposed, since it attacks the non-GCC side as
well, and it revamps the code to make the "unused and never-tested
macro" bug less likely in the future.
2003-10-21 Paul Eggert <address@hidden>
* obstack.h (obstack_1grow_fast): Properly parenthesize arg.
(obstack_ptr_grow_fast, obstack_int_grow_fast):
Don't use lvalue casts, as GCC plans to remove support for them
in GCC 3.5. Reported by Joseph S. Meyers. This bug
was also present in the non-GCC version, indicating that this
code had always been buggy and had never been widely used.
(obstack_1grow, obstack_ptr_grow, obstack_int_grow, obstack_blank):
Use the fast variant of each macro, rather than copying the
definiens of the fast variant; that way, we'll be more likely to
catch future bugs in the fast variants.
Index: obstack.h
===================================================================
RCS file: /cvsroot/gnulib/gnulib/lib/obstack.h,v
retrieving revision 1.23
diff -p -u -r1.23 obstack.h
--- obstack.h 9 Sep 2003 23:00:43 -0000 1.23
+++ obstack.h 22 Oct 2003 00:59:13 -0000
@@ -274,7 +274,7 @@ extern int obstack_exit_failure;
# define obstack_freefun(h, newfreefun) \
((h) -> freefun = (void (*)(void *, struct _obstack_chunk *)) (newfreefun))
-#define obstack_1grow_fast(h,achar) (*((h)->next_free)++ = achar)
+#define obstack_1grow_fast(h,achar) (*((h)->next_free)++ = (achar))
#define obstack_blank_fast(h,n) ((h)->next_free += (n))
@@ -342,7 +342,7 @@ __extension__
\
({ struct obstack *__o = (OBSTACK); \
if (__o->next_free + 1 > __o->chunk_limit) \
_obstack_newchunk (__o, 1); \
- *(__o->next_free)++ = (datum); \
+ obstack_1grow_fast (__o, datum); \
(void) 0; })
/* These assume that the obstack alignment is good enough for pointers
@@ -354,22 +354,28 @@ __extension__
\
({ struct obstack *__o = (OBSTACK); \
if (__o->next_free + sizeof (void *) > __o->chunk_limit) \
_obstack_newchunk (__o, sizeof (void *)); \
- *((void **)__o->next_free)++ = (datum); \
- (void) 0; })
+ obstack_ptr_grow_fast (__o, datum); }) \
# define obstack_int_grow(OBSTACK,datum) \
__extension__ \
({ struct obstack *__o = (OBSTACK); \
if (__o->next_free + sizeof (int) > __o->chunk_limit) \
_obstack_newchunk (__o, sizeof (int)); \
- *((int *)__o->next_free)++ = (datum); \
- (void) 0; })
+ obstack_int_grow_fast (__o, datum); })
-# define obstack_ptr_grow_fast(h,aptr) \
- (*((void **) (h)->next_free)++ = (aptr))
+# define obstack_ptr_grow_fast(OBSTACK,aptr) \
+__extension__ \
+({ struct obstack *__o1 = (OBSTACK); \
+ *(const void **) __o1->next_free = (aptr); \
+ __o1->next_free += sizeof (const void *); \
+ (void) 0; })
-# define obstack_int_grow_fast(h,aint) \
- (*((int *) (h)->next_free)++ = (aint))
+# define obstack_int_grow_fast(OBSTACK,aint) \
+__extension__ \
+({ struct obstack *__o1 = (OBSTACK); \
+ *(int *) __o1->next_free = (aint); \
+ __o1->next_free += sizeof (int); \
+ (void) 0; })
# define obstack_blank(OBSTACK,length) \
__extension__ \
@@ -377,7 +383,7 @@ __extension__
\
int __len = (length); \
if (__o->chunk_limit - __o->next_free < __len) \
_obstack_newchunk (__o, __len); \
- __o->next_free += __len; \
+ obstack_blank_fast (__o, __len); \
(void) 0; })
# define obstack_alloc(OBSTACK,length) \
@@ -464,29 +470,29 @@ __extension__
\
# define obstack_1grow(h,datum)
\
( (((h)->next_free + 1 > (h)->chunk_limit) \
? (_obstack_newchunk ((h), 1), 0) : 0), \
- (*((h)->next_free)++ = (datum)))
+ obstack_1grow_fast (h, datum))
# define obstack_ptr_grow(h,datum) \
( (((h)->next_free + sizeof (char *) > (h)->chunk_limit) \
? (_obstack_newchunk ((h), sizeof (char *)), 0) : 0), \
- (*((const char **) (((h)->next_free+=sizeof(char *))-sizeof(char *))) =
(datum)))
+ obstack_ptr_grow_fast (h, datum))
# define obstack_int_grow(h,datum) \
( (((h)->next_free + sizeof (int) > (h)->chunk_limit) \
? (_obstack_newchunk ((h), sizeof (int)), 0) : 0), \
- (*((int *) (((h)->next_free+=sizeof(int))-sizeof(int))) = (datum)))
+ obstack_int_grow_fast (h, datum))
# define obstack_ptr_grow_fast(h,aptr) \
- (*((const char **) (h)->next_free)++ = (aptr))
+ (((const void **) ((h)->next_free += sizeof (void *)))[-1] = (aptr))
# define obstack_int_grow_fast(h,aint) \
- (*((int *) (h)->next_free)++ = (aint))
+ (((int *) ((h)->next_free += sizeof (int)))[-1] = (aptr))
# define obstack_blank(h,length) \
( (h)->temp = (length),
\
(((h)->chunk_limit - (h)->next_free < (h)->temp) \
? (_obstack_newchunk ((h), (h)->temp), 0) : 0), \
- ((h)->next_free += (h)->temp))
+ obstack_blank_fast (h, (h)->temp))
# define obstack_alloc(h,length) \
(obstack_blank ((h), (length)), obstack_finish ((h)))