erofs: Eliminate usage of uninitialized_var() macro
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Message ID 20200615040141.3627746-1-yanaijie@huawei.com
State New
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Series
  • erofs: Eliminate usage of uninitialized_var() macro
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Commit Message

Jason Yan June 15, 2020, 4:01 a.m. UTC
This is an effort to eliminate the uninitialized_var() macro[1].

The use of this macro is the wrong solution because it forces off ANY
analysis by the compiler for a given variable. It even masks "unused
variable" warnings.

Quoted from Linus[2]:

"It's a horrible thing to use, in that it adds extra cruft to the
source code, and then shuts up a compiler warning (even the _reliable_
warnings from gcc)."

The gcc option "-Wmaybe-uninitialized" has been disabled and this change
will not produce any warnnings even with "make W=1".

[1] https://github.com/KSPP/linux/issues/81
[2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/

Cc: Kees Cook <keescook@chromium.org>
Cc: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
---
 fs/erofs/data.c  | 4 ++--
 fs/erofs/zdata.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

Comments

Gao Xiang June 15, 2020, 7:25 a.m. UTC | #1
Hi Jason,

On Mon, Jun 15, 2020 at 12:01:41PM +0800, Jason Yan wrote:
> This is an effort to eliminate the uninitialized_var() macro[1].
> 
> The use of this macro is the wrong solution because it forces off ANY
> analysis by the compiler for a given variable. It even masks "unused
> variable" warnings.
> 
> Quoted from Linus[2]:
> 
> "It's a horrible thing to use, in that it adds extra cruft to the
> source code, and then shuts up a compiler warning (even the _reliable_
> warnings from gcc)."
> 
> The gcc option "-Wmaybe-uninitialized" has been disabled and this change
> will not produce any warnnings even with "make W=1".
> 
> [1] https://github.com/KSPP/linux/issues/81
> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
> 
> Cc: Kees Cook <keescook@chromium.org>
> Cc: Chao Yu <yuchao0@huawei.com>
> Signed-off-by: Jason Yan <yanaijie@huawei.com>
> ---

I'm fine with the patch since "-Wmaybe-uninitialized" has been disabled and
I've also asked Kees for it in private previously.

I still remembered that Kees sent out a treewide patch. Sorry about that
I don't catch up it... But what is wrong with the original patchset?

Thanks,
Gao Xiang
Jason Yan June 15, 2020, 7:43 a.m. UTC | #2
在 2020/6/15 15:25, Gao Xiang 写道:
> Hi Jason,
> 
> On Mon, Jun 15, 2020 at 12:01:41PM +0800, Jason Yan wrote:
>> This is an effort to eliminate the uninitialized_var() macro[1].
>>
>> The use of this macro is the wrong solution because it forces off ANY
>> analysis by the compiler for a given variable. It even masks "unused
>> variable" warnings.
>>
>> Quoted from Linus[2]:
>>
>> "It's a horrible thing to use, in that it adds extra cruft to the
>> source code, and then shuts up a compiler warning (even the _reliable_
>> warnings from gcc)."
>>
>> The gcc option "-Wmaybe-uninitialized" has been disabled and this change
>> will not produce any warnnings even with "make W=1".
>>
>> [1] https://github.com/KSPP/linux/issues/81
>> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
>>
>> Cc: Kees Cook <keescook@chromium.org>
>> Cc: Chao Yu <yuchao0@huawei.com>
>> Signed-off-by: Jason Yan <yanaijie@huawei.com>
>> ---
> 
> I'm fine with the patch since "-Wmaybe-uninitialized" has been disabled and
> I've also asked Kees for it in private previously.
> 
> I still remembered that Kees sent out a treewide patch. Sorry about that
> I don't catch up it... But what is wrong with the original patchset?
> 

Yes, Kees has remind me of that and I will let him handle it. So you can 
ignore this patch.

Thanks,
Jason

> Thanks,
> Gao Xiang
> 
> 
> .
>
Chao Yu June 15, 2020, 8:29 a.m. UTC | #3
On 2020/6/15 16:07, Gao Xiang wrote:
> On Mon, Jun 15, 2020 at 03:43:09PM +0800, Jason Yan wrote:
>>
>>
>> 鍦?2020/6/15 15:25, Gao Xiang 鍐欓亾:
>>> Hi Jason,
>>>
>>> On Mon, Jun 15, 2020 at 12:01:41PM +0800, Jason Yan wrote:
>>>> This is an effort to eliminate the uninitialized_var() macro[1].
>>>>
>>>> The use of this macro is the wrong solution because it forces off ANY
>>>> analysis by the compiler for a given variable. It even masks "unused
>>>> variable" warnings.
>>>>
>>>> Quoted from Linus[2]:
>>>>
>>>> "It's a horrible thing to use, in that it adds extra cruft to the
>>>> source code, and then shuts up a compiler warning (even the _reliable_
>>>> warnings from gcc)."
>>>>
>>>> The gcc option "-Wmaybe-uninitialized" has been disabled and this change
>>>> will not produce any warnnings even with "make W=1".
>>>>
>>>> [1] https://github.com/KSPP/linux/issues/81
>>>> [2] https://lore.kernel.org/lkml/CA+55aFz2500WfbKXAx8s67wrm9=yVJu65TpLgN_ybYNv0VEOKA@mail.gmail.com/
>>>>
>>>> Cc: Kees Cook <keescook@chromium.org>
>>>> Cc: Chao Yu <yuchao0@huawei.com>
>>>> Signed-off-by: Jason Yan <yanaijie@huawei.com>
>>>> ---
>>>
>>> I'm fine with the patch since "-Wmaybe-uninitialized" has been disabled and
>>> I've also asked Kees for it in private previously.
>>>
>>> I still remembered that Kees sent out a treewide patch. Sorry about that
>>> I don't catch up it... But what is wrong with the original patchset?
>>>
>>
>> Yes, Kees has remind me of that and I will let him handle it. So you can
>> ignore this patch.
> 
> Okay, I was just wondering if this part should be send out via EROFS tree
> for this cycle. However if there was an automatic generated patch by Kees,
> I think perhaps Linus could pick them out directly. But anyway, both ways
> are fine with me. ;) Ping me when needed.

Either way is okay to me.

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,

> 
> Thanks,
> Gao Xiang
> 
>>
>> Thanks,
>> Jason
>>
>>> Thanks,
>>> Gao Xiang
>>>
>>>
>>> .
>>>
>>
> 
> .
>

Patch
diff mbox series

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index 64b56c7df023..d0542151e8c4 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -265,7 +265,7 @@  static inline struct bio *erofs_read_raw_page(struct bio *bio,
  */
 static int erofs_raw_access_readpage(struct file *file, struct page *page)
 {
-	erofs_off_t uninitialized_var(last_block);
+	erofs_off_t last_block;
 	struct bio *bio;
 
 	trace_erofs_readpage(page, true);
@@ -282,7 +282,7 @@  static int erofs_raw_access_readpage(struct file *file, struct page *page)
 
 static void erofs_raw_access_readahead(struct readahead_control *rac)
 {
-	erofs_off_t uninitialized_var(last_block);
+	erofs_off_t last_block;
 	struct bio *bio = NULL;
 	struct page *page;
 
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index be50a4d9d273..24a26aaf847f 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1161,7 +1161,7 @@  static void z_erofs_submit_queue(struct super_block *sb,
 	struct z_erofs_decompressqueue *q[NR_JOBQUEUES];
 	void *bi_private;
 	/* since bio will be NULL, no need to initialize last_index */
-	pgoff_t uninitialized_var(last_index);
+	pgoff_t last_index;
 	unsigned int nr_bios = 0;
 	struct bio *bio = NULL;