Re: [PATCH] silence gcc warning about possibly uninitialized use of variable in scsi_scan

Re: [PATCH] silence gcc warning about possibly uninitialized use of variable in scsi_scan

[James Bottomley]

On Sun, 2006-02-26 at 16:39 +0100, Jesper Juhl wrote:
> Gcc can't see that 'result' will always be initialized inside the for loop
> and thus it warns
>   drivers/scsi/scsi_scan.c:445: warning: 'result' might be used uninitialized in this function
> This patch silences the warning by initializing 'result' to zero.

Really, this is a gcc bug.  My version of the compiler:

gcc version 4.0.3 20051201 (prerelease) (Debian 4.0.2-5)

Doesn't give this warning.  And, since the loop has fixed parameters,
gcc should see not only that it's always executed, but that it could be
unrolled.

Which version is causing the problem?

James

Re: [PATCH] silence gcc warning about possibly uninitialized use of variable in scsi_scan

[Jesper Juhl]

On 2/26/06, James Bottomley <James.Bottomley@steeleye.com> wrote:
> On Sun, 2006-02-26 at 16:39 +0100, Jesper Juhl wrote:
> > Gcc can't see that 'result' will always be initialized inside the for loop
> > and thus it warns
> >   drivers/scsi/scsi_scan.c:445: warning: 'result' might be used uninitialized in this function
> > This patch silences the warning by initializing 'result' to zero.
>
> Really, this is a gcc bug.  My version of the compiler:
>
> gcc version 4.0.3 20051201 (prerelease) (Debian 4.0.2-5)
>
> Doesn't give this warning.  And, since the loop has fixed parameters,
> gcc should see not only that it's always executed, but that it could be
> unrolled.
>
> Which version is causing the problem?
>
2.6.16-rc4-mm2 build with gcc 3.4.5

and I agree that gcc really should be noticing, but in fact it
doesn't. It's no big deal, I just thought we might want to shut gcc up
and give people one less warning to worry about.

--
Jesper Juhl <jesper.juhl@gmail.com>
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Re: [PATCH] silence gcc warning about possibly uninitialized use of variable in scsi_scan

[James Bottomley]

On Sun, 2006-02-26 at 19:23 +0100, Jesper Juhl wrote:
> > gcc version 4.0.3 20051201 (prerelease) (Debian 4.0.2-5)
> >
> > Doesn't give this warning.  And, since the loop has fixed parameters,
> > gcc should see not only that it's always executed, but that it could be
> > unrolled.
> >
> > Which version is causing the problem?
> >
> 2.6.16-rc4-mm2 build with gcc 3.4.5

I also tried with

gcc version 3.3.5 (Debian 1:3.3.5-13)

which likewise fails to give this warning, so I really think this is a
bug in your particular version of gcc.

James


> and I agree that gcc really should be noticing, but in fact it
> doesn't. It's no big deal, I just thought we might want to shut gcc up
> and give people one less warning to worry about.
> 
> --
> Jesper Juhl <jesper.juhl@gmail.com>
> Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
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Re: [PATCH] silence gcc warning about possibly uninitialized use of variable in scsi_scan

[Jesper Juhl]

On 2/26/06, James Bottomley <James.Bottomley@steeleye.com> wrote:
> On Sun, 2006-02-26 at 19:23 +0100, Jesper Juhl wrote:
> > > gcc version 4.0.3 20051201 (prerelease) (Debian 4.0.2-5)
> > >
> > > Doesn't give this warning.  And, since the loop has fixed parameters,
> > > gcc should see not only that it's always executed, but that it could be
> > > unrolled.
> > >
> > > Which version is causing the problem?
> > >
> > 2.6.16-rc4-mm2 build with gcc 3.4.5
>
> I also tried with
>
> gcc version 3.3.5 (Debian 1:3.3.5-13)
>
> which likewise fails to give this warning, so I really think this is a
> bug in your particular version of gcc.
>

Hmm, it's quite reproducible and the gcc 3.4.5 I have here is not
patched by the distribution (Slackware). If you want I can send you
the .config that results in the warning..

--
Jesper Juhl <jesper.juhl@gmail.com>
Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please      http://www.expita.com/nomime.html

Re: [PATCH] silence gcc warning about possibly uninitialized use of variable in scsi_scan

[James Bottomley]

On Sun, 2006-02-26 at 20:01 +0100, Jesper Juhl wrote:
> Hmm, it's quite reproducible and the gcc 3.4.5 I have here is not
> patched by the distribution (Slackware). If you want I can send you
> the .config that results in the warning..

I really don't think it's a config issue.  scsi_probe_lun() is always
compiled in if CONFIG_SCSI is set.  I think you have a compiler problem.

James

Re: [PATCH] silence gcc warning about possibly uninitialized use of variable in scsi_scan

[Jesper Juhl]

On 2/26/06, James Bottomley <James.Bottomley@steeleye.com> wrote:
> On Sun, 2006-02-26 at 20:01 +0100, Jesper Juhl wrote:
> > Hmm, it's quite reproducible and the gcc 3.4.5 I have here is not
> > patched by the distribution (Slackware). If you want I can send you
> > the .config that results in the warning..
>
> I really don't think it's a config issue.  scsi_probe_lun() is always
> compiled in if CONFIG_SCSI is set.  I think you have a compiler problem.
>

I must admit I think the compiler is OK.
I have two different boxes with gcc 3.4.5 and they both give the same
warning (not to mention that that gcc builds everything I've thrown at
it correctly).
But nevermind, it's just a silly little warning - just leave it be.

--
Jesper Juhl <jesper.juhl@gmail.com>
Don't top-post  http://www.catb.org/~esr/jargon/html/T/top-post.html
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