[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #1 from pinskia at gmail dot com 2007-09-02 13:26 ---
Subject: Re: New: Failed to warn uninitialized stack variable
On 2 Sep 2007 13:19:45 -, hjl at lucon dot org
[EMAIL PROTECTED] wrote:
[EMAIL PROTECTED] uninit-2]$ cat x.c
typedef int mpz_t[1];
typedef struct iterator_stack
{
struct iterator_stack *prev;
mpz_t value;
} iterator_stack;
iterator_stack *x;
void bar (mpz_t);
void
foo ()
{
iterator_stack frame;
bar (frame.value);
x = frame.prev;
}
[EMAIL PROTECTED] uninit-2]$ make
/export/build/gnu/gcc/build-x86_64-linux/gcc/xgcc
-B/export/build/gnu/gcc/build-x86_64-linux/gcc/ -O2 -Wuninitialized -S x.c
Not really because this is the same as
bar (frame.value[0]);
Where bar can do pointer tricks to get back to original struct and
then change prev, trust me, this is allowed. There is a comment in
GCC sources about this specific issue.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #2 from pinskia at gcc dot gnu dot org 2007-09-02 13:32 --- As mentioned by me in comment #1, we cannot warn about this. -- pinskia at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #3 from hjl at lucon dot org 2007-09-02 13:37 --- Subject: Re: New: Failed to warn uninitialized stack variable Not really because this is the same as bar (frame.value[0]); Where bar can do pointer tricks to get back to original struct and then change prev, trust me, this is allowed. There is a comment in GCC sources about this specific issue. How does bar know it is called by bar (frame.value); not mpz_t value; ... bar (value); -- hjl at lucon dot org changed: What|Removed |Added Status|RESOLVED|UNCONFIRMED Resolution|INVALID | http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #4 from pinskia at gcc dot gnu dot org 2007-09-02 13:43 --- bar (frame.value); That call to bar causes the whole frame struct escapes here, not just the array element. void bar (mpz_t); is really: void bar(int*); because of array decaying in parameters. Again with pointer arithmetic, bar can get back to the original struct and be able to set prev. So again there is no bug here. -- pinskia at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #5 from hjl at lucon dot org 2007-09-02 13:56 ---
(In reply to comment #4)
bar (frame.value);
That call to bar causes the whole frame struct escapes here, not just the
array
element.
void bar (mpz_t);
is really:
void bar(int*);
because of array decaying in parameters.
Again with pointer arithmetic, bar can get back to the original struct and be
able to set prev. So again there is no bug here.
When bar is called from
mpz_t value;
...
bar (value);
there is no original struct to go back to and there can be another
struct
typedef struct iterator_stack_2
{
struct iterator_stack_2 *prev;
mpz_t value;
int foo;
} iterator_stack_2;
iterator_stack_2 x;
..
bar (x.value);
What does bar get back to? Are you saying if a pointer is passed to bar,
it can get back to any original struct where the pointer is a field?
--
hjl at lucon dot org changed:
What|Removed |Added
Status|RESOLVED|UNCONFIRMED
Resolution|INVALID |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #6 from hjl at lucon dot org 2007-09-02 13:58 --- (In reply to comment #5) What does bar get back to? Are you saying if a pointer is passed to bar, it can get back to any original struct where the pointer is a field? If you can write such a function, I can pass you a pointer and your function will be wrong. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
Re: [Bug middle-end/33279] Failed to warn uninitialized stack variable
On 2 Sep 2007 13:56:13 -, hjl at lucon dot org [EMAIL PROTECTED] wrote: What does bar get back to? Are you saying if a pointer is passed to bar, it can get back to any original struct where the pointer is a field? It only matters at the context at the point bar is called with the struct. No other place matters. It does not matter if bar can be called with a simple array (that will cause undefined code if bar tries to go before the array) as it still can be using pointer arithmetic.
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #7 from pinskia at gmail dot com 2007-09-02 14:01 --- Subject: Re: Failed to warn uninitialized stack variable On 2 Sep 2007 13:56:13 -, hjl at lucon dot org [EMAIL PROTECTED] wrote: What does bar get back to? Are you saying if a pointer is passed to bar, it can get back to any original struct where the pointer is a field? It only matters at the context at the point bar is called with the struct. No other place matters. It does not matter if bar can be called with a simple array (that will cause undefined code if bar tries to go before the array) as it still can be using pointer arithmetic. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
Re: [Bug middle-end/33279] Failed to warn uninitialized stack variable
On 2 Sep 2007 13:58:23 -, hjl at lucon dot org [EMAIL PROTECTED] wrote: If you can write such a function, I can pass you a pointer and your function will be wrong. yes so but that call would be undefined, not the one we are talking about currently. --Pinski
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #8 from pinskia at gmail dot com 2007-09-02 14:02 --- Subject: Re: Failed to warn uninitialized stack variable On 2 Sep 2007 13:58:23 -, hjl at lucon dot org [EMAIL PROTECTED] wrote: If you can write such a function, I can pass you a pointer and your function will be wrong. yes so but that call would be undefined, not the one we are talking about currently. --Pinski -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #9 from rguenth at gcc dot gnu dot org 2007-09-02 14:03 --- What does bar get back to? Are you saying if a pointer is passed to bar, it can get back to any original struct where the pointer is a field? No, but if you pass a pointer to a field of a struct the callee may derive the address of the containing object and modify it. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
[Bug middle-end/33279] Failed to warn uninitialized stack variable
--- Comment #10 from pinskia at gcc dot gnu dot org 2007-09-02 17:19 --- As mentioned by Richard and I, this bug is invalid. -- pinskia at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33279
