[libvirt] Compiler warnings

[Alex Jia]

On 10/18/2011 10:09 AM, Wen Congyang wrote:
> At 10/18/2011 09:32 AM, Wen Congyang Write:
>> At 10/18/2011 01:04 AM, Eric Blake Write:
>>> On 10/17/2011 11:03 AM, Eric Blake wrote:
>>>> On 10/17/2011 10:17 AM, Alex Jia wrote:
>>>>> Eric,
>>>>> It's latest libvirt upstream, current commit id is commit 0a71c79.
>>>>>
>>>>> # rpm -q glibc
>>>>> glibc-2.12-1.42.el6.x86_64
>>>>>
>>>>> 430 if (strchr(toescape, *cur))
>>>>>>> CC libvirt_util_la-buf.lo
>>>>>>> util/buf.c: In function 'virBufferEscape':
>>>>>>> util/buf.c:430: warning: logical '&&' with non-zero constant will
>>>>>>> always
>>>>>>> evaluate as true [-Wlogical-op]
>>>> Something's screwy. There's no&&  in that line, unless strchr() is a
>>>> macro based on your particular compilation flags. I'm suspecting that
>>>> this is a case of -D_FORTIFY_SOURCE going awry. I don't see how this
>>>> could possibly be a libvirt issue; more likely, it is an issue with the
>>>> choice of compiler flags you are using, coupled with an issue in the
>>>> system headers causing the preprocessor to expand strchr() into
>>>> something that tickles a spurious gcc warning.
>>> Just to make sure, could you show 'make V=1' output, so we know exactly
>>> which compiler flags are in effect?
>>>
>> I can reproduce this problem, here is 'make V=1' output:
>>
>> =====================================================
>> make[3]: Entering directory `/root/rpmbuild/BUILD/libvirt-0.9.6/src'
>> /bin/sh ../libtool  --tag=CC   --mode=compile gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I.. -I../gnulib/lib -I../gnulib/lib -I../include -I../src/util -I../include -DIN_LIBVIRT        -I/usr/include/libxml2   -Wall -W -Wformat-y2k -Wformat-security -Winit-self -Wmissing-include-dirs -Wunused -Wunknown-pragmas -Wstrict-aliasing -Wshadow -Wpointer-arith -Wbad-function-cast -Wcast-align -Wwrite-strings -Wlogical-op -Waggregate-return -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -Wmissing-noreturn -Wmissing-format-attribute -Wredundant-decls -Wnested-externs -Winline -Winvalid-pch -Wvolatile-register-var -Wdisabled-optimization -Wbuiltin-macro-redefined -Wmudflap -Wpacked-bitfield-compat -Wsync-nand -Wattributes -Wcoverage-mismatch -Wmultichar -Wno-missing-field-initializers -Wno-sign-compare -Wframe-larger-than=4096 -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-all --param=ssp-buffer-size=4 -fexceptions -fasynchronous-unwind-tables -fdiagnostics
> -s
>> how-option -funit-at-a-time -Werror      -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -MT libvirt_util_la-buf.lo -MD -MP -MF .deps/libvirt_util_la-buf.Tpo -c -o libvirt_util_la-buf.lo `test -f 'util/buf.c' || echo './'`util/buf.c
>> libtool: compile:  gcc -std=gnu99 -DHAVE_CONFIG_H -I. -I.. -I../gnulib/lib -I../gnulib/lib -I../include -I../src/util -I../include -DIN_LIBVIRT -I/usr/include/libxml2 -Wall -W -Wformat-y2k -Wformat-security -Winit-self -Wmissing-include-dirs -Wunused -Wunknown-pragmas -Wstrict-aliasing -Wshadow -Wpointer-arith -Wbad-function-cast -Wcast-align -Wwrite-strings -Wlogical-op -Waggregate-return -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-declarations -Wmissing-noreturn -Wmissing-format-attribute -Wredundant-decls -Wnested-externs -Winline -Winvalid-pch -Wvolatile-register-var -Wdisabled-optimization -Wbuiltin-macro-redefined -Wmudflap -Wpacked-bitfield-compat -Wsync-nand -Wattributes -Wcoverage-mismatch -Wmultichar -Wno-missing-field-initializers -Wno-sign-compare -Wframe-larger-than=4096 -Wp,-D_FORTIFY_SOURCE=2 -fstack-protector-all --param=ssp-buffer-size=4 -fexceptions -fasynchronous-unwind-tables -fdiagnostics-show-option -funit-at-a-time -Werro
> r
>> -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -MT libvirt_util_la-buf.lo -MD -MP -MF .deps/libvirt_util_la-buf.Tpo -c util/buf.c  -fPIC -DPIC -o .libs/libvirt_util_la-buf.o
>> cc1: warnings being treated as errors
>> util/buf.c: In function 'virBufferEscape':
>> util/buf.c:430: error: logical '&&' with non-zero constant will always evaluate as true [-Wlogical-op]
>> make[3]: *** [libvirt_util_la-buf.lo] Error 1
>> =====================================================
>>
>> If I remove -O2, I can build util/buf.c.
> I test strchr in a small program:
> =====================================================
> # cat test.c
> #include<stdio.h>
> #include<string.h>
>
> int main() {
>      char *s = "abcdefg";
>      int chr = (int)'d';
>      char *d;
>
>      d = strchr(s, chr);
>      if (d)
>          printf("%s\n", d);
>
>      return 0;
> }
> # gcc -std=c99 -Wall -o test test.c -Wlogical-op -Werror
> # gcc -std=c99 -O2 -Wall -o test test.c -Wlogical-op -Werror
> cc1: warnings being treated as errors
> test.c: In function ‘main’:
> test.c:9: error: logical ‘&&’ with non-zero constant will always evaluate as true
> # gcc -std=c99 -Wall -o test test.c -Wlogical-op -Werror
> # gcc -std=c99 -Wall -o test test.c -Werror
> =====================================================
>
> The building failed only when '-O2' and '-Wlogical-op' are specified at the same time.
>
> Thanks
> Wen Congyang
Chonyang, thanks for your reply and good example.

Regards,
Alex
>> I am still investigating this problem.
>>
>> Thanks
>> Wen Congyang
>>
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