2020-06-15 04:03:45

by Jason Yan

Subject: [PATCH] f2fs: Eliminate usage of uninitialized_var() macro

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 <[email protected]>
Signed-off-by: Jason Yan <[email protected]>
---
fs/f2fs/data.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 326c63879ddc..e6ec61274d76 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
};
#endif
int nr_pages;
- pgoff_t uninitialized_var(writeback_index);
+ pgoff_t writeback_index;
pgoff_t index;
pgoff_t end; /* Inclusive */
pgoff_t done_index;
--
2.25.4

2020-06-15 08:29:37

by Chao Yu

Subject: Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized_var() macro

On 2020/6/15 12:02, 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 <[email protected]>
> Signed-off-by: Jason Yan <[email protected]>
> ---
> fs/f2fs/data.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index 326c63879ddc..e6ec61274d76 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
> };
> #endif
> int nr_pages;
> - pgoff_t uninitialized_var(writeback_index);
> + pgoff_t writeback_index;

I suggest to delete this variable directly, as we did for mm in
commit 28659cc8cc87 (mm/page-writeback.c: remove unused variable).

Thanks,

> pgoff_t index;
> pgoff_t end; /* Inclusive */
> pgoff_t done_index;
>

2020-06-15 08:41:23

by Jason Yan

Subject: Re: [f2fs-dev] [PATCH] f2fs: Eliminate usage of uninitialized_var() macro

在 2020/6/15 16:26, Chao Yu 写道:
> On 2020/6/15 12:02, 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 <[email protected]>
>> Signed-off-by: Jason Yan <[email protected]>
>> ---
>> fs/f2fs/data.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 326c63879ddc..e6ec61274d76 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -2856,7 +2856,7 @@ static int f2fs_write_cache_pages(struct address_space *mapping,
>> };
>> #endif
>> int nr_pages;
>> - pgoff_t uninitialized_var(writeback_index);
>> + pgoff_t writeback_index;
>
> I suggest to delete this variable directly, as we did for mm in
> commit 28659cc8cc87 (mm/page-writeback.c: remove unused variable).
>

Good suggestion, I will send v2.

Thanks,
Jason

> Thanks,
>
>> pgoff_t index;
>> pgoff_t end; /* Inclusive */
>> pgoff_t done_index;
>>
>
> .
>