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Subject: |
Gcc 4.8.2 -Werror=maybe-unused warning in dfa.c |
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Date: |
Wed, 11 Jun 2014 23:39:32 +0930 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 |
G'day,
Just upgraded to a recent release of gcc (previously I was running
4.7.x):
$ gcc --version
gcc (Gentoo 4.8.2 p1.3r1, pie-0.5.8r1) 4.8.2
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
It complains about an stack variable, mbclen, possibly being
used uninitialised in a call to transit_state_consume_1char.
The warning message is (I'm still at 2.20 post-admin commit
....78f07b8c8e26):
make[2]: Entering directory `/home/grep-gnu/grep/src'
CC dfa.o
dfa.c: In function 'transit_state':
dfa.c:3213:31: error: 'mbclen' may be used uninitialized in this function
[-Werror=maybe-uninitialized]
transit_state_consume_1char (d, s, pp, wc, mbclen, match_lens);
^
cc1: all warnings being treated as errors
make[2]: *** [dfa.o] Error 1
make[2]: Leaving directory `/home/grep-gnu/grep/src
The earlier version of gcc did not complain about this code.
Reading through the code, it looks that the offending line is
only reached if (nelem > 0), and, if so, mbclen is initialised
earlier. At the expense of some code duplication, or perhaps
the judicious use of a couple of goto's, the
(nelem == 0 || maxlen == 0) block could be split up and rearranged
such that the connection between the preceding paragraph
(nelem > 0) and the following paragraphs (transit_state_consume_1char)
would become more apparent, and the fact that mbclen is always
initialised would become clear, both to the reader and the
compiler.
cheers,
behoffski (Brenton Hoff)
Programmer, Grouse Software
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--- Begin Message ---
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Subject: |
Re: bug#17754: Gcc 4.8.2 -Werror=maybe-unused warning in dfa.c |
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Date: |
Wed, 11 Jun 2014 08:08:26 -0700 |
On Wed, Jun 11, 2014 at 7:09 AM, behoffski <address@hidden> wrote:
> G'day,
>
> Just upgraded to a recent release of gcc (previously I was running
> 4.7.x):
> $ gcc --version
> gcc (Gentoo 4.8.2 p1.3r1, pie-0.5.8r1) 4.8.2
> Copyright (C) 2013 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions. There is
> NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> PURPOSE.
>
> It complains about an stack variable, mbclen, possibly being
> used uninitialised in a call to transit_state_consume_1char.
>
> The warning message is (I'm still at 2.20 post-admin commit
> ....78f07b8c8e26):
>
> make[2]: Entering directory `/home/grep-gnu/grep/src'
> CC dfa.o
> dfa.c: In function 'transit_state':
> dfa.c:3213:31: error: 'mbclen' may be used uninitialized in this
> function [-Werror=maybe-uninitialized]
> transit_state_consume_1char (d, s, pp, wc, mbclen, match_lens);
> ^
> cc1: all warnings being treated as errors
> make[2]: *** [dfa.o] Error 1
> make[2]: Leaving directory `/home/grep-gnu/grep/src
>
> The earlier version of gcc did not complain about this code.
Thanks for the report, but...
With gcc-4.9, I don't see that warning, so I suspect gcc's flow
analysis has improved enough that it determines there is no
risk of use-uninitialized there. Also, gcc's 4.8.2->4.8.3 delta
fixed many bugs, so if you require 4.8.x, it's probably
better to use 4.8.3.
When enabling warnings, it's best to use the most recent version
of gcc and e.g., glibc header files possible. Otherwise, we end
up with false positives like this.
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