[OpenWrt-Devel] [PATCH uci 2/2] build: Add -Wclobbered to detect problems with longjmp

[Hauke Mehrtens]

On 11/5/19 1:27 AM, Petr Štetiar wrote:
> Hi,
> 
> Hauke Mehrtens <hauke at hauke-m.de> [2019-11-01 17:06:34]:
> 
>> +ADD_DEFINITIONS(-Os -Wall -Werror -Wclobbered --std=gnu99 -g3 -I. -DUCI_PREFIX="${CMAKE_INSTALL_PREFIX}")
> 
> is there any reason to not use -Wextra directly?

I was looking on how we could prevent to have a similar problem as the
one described in CVE-2019-15513 and found this warning which should have
warned us about this problem. First I was trying to understand this CVE
and then I wanted to learn from it to prevent such problems next time.

I support adding -Wextra it is even better.

> 
>  list.c:140:11: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  file.c:572:51: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  file.c:850:15: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  file.c:865:15: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  delta.c:199:6: error: this statement may fall through [-Werror=implicit-fallthrough=]
>  parse.c:80:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
>  parse.c:81:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
>  file.c:572:51: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  file.c:850:15: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  file.c:865:15: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  delta.c:199:6: error: this statement may fall through [-Werror=implicit-fallthrough=]
>  parse.c:80:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
>  parse.c:81:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
>  ucimap.c:146:16: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:151:17: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:243:34: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:247:9: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:254:39: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:258:9: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:285:34: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:363:17: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:563:12: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:753:18: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
>  ucimap.c:879:17: error: comparison between signed and unsigned integer expressions [-Werror=sign-compare]
> 
> Yousong Zhou <yszhou4tech at gmail.com> [2019-11-04 11:29:05]:
> 
>> The -Wclobber check can produce false-positives right?
> 
> I didn't looked deeper, but GCC 6,7,8,9 on x86/64 reports following:
> 
>  list.c:626:21: error: variable ‘prev’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
>   626 |  struct uci_option *prev = NULL;
>       |                     ^~~~
> 
>  list.c:627:14: error: variable ‘value2’ might be clobbered by ‘longjmp’ or ‘vfork’ [-Werror=clobbered]
>   627 |  const char *value2 = NULL;
>       |              ^~~~~~

I think I also saw these problems in my manual review, but the
-Wclobbered did not complain about them for me with gcc 8.3 on MIPS.

> 
> but clang 9,10 on x86/64 doesn't.
> 
> -- ynezz
> 

Hauke

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