Re: [Qemu-devel] [PATCH] Fix compilation on GCC 4.5

[Stefan Weil <sw@weilnetz.de>]

Am 03.10.2012 21:49, schrieb Søren Sandmann:
> Stefan Weil<sw@weilnetz.de>  writes:
>
>> I don't see any warnings with gcc Debian 4.4.5-8.
>>
>> Could you please provide more information on your environment
>> and the warnings which you get?
>>
>> Here is a macro which simplifies the version check:
>>
>> #if QEMU_GNUC_PREREQ(4, 6)
>>
>> Regards
>>
>> Stefan Weil
>
> With this compiler:
>
>      dhcp-100-3-184:~/vertigo/qemu% gcc -v
>      Using built-in specs.
>      COLLECT_GCC=/usr/bin/gcc
>      COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-redhat-linux/4.5.1/lto-wrapper
>      Target: x86_64-redhat-linux
>      Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
>      --infodir=/usr/share/info
>      --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap
>      --enable-shared --enable-threads=posix --enable-checking=release
>      --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions
>      --enable-gnu-unique-object --enable-linker-build-id
>      --enable-languages=c,c++,objc,obj-c++,java,fortran,ada,lto
>      --enable-plugin --enable-java-awt=gtk --disable-dssi
>      --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
>      --enable-libgcj-multifile --enable-java-maintainer-mode
>      --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
>      --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic
>      --with-arch_32=i686 --build=x86_64-redhat-linux
>      Thread model: posix
>      gcc version 4.5.1 20100924 (Red Hat 4.5.1-4) (GCC)
>
> This is the error I get:
>
>      make  BUILD_DIR=/home/ssp/vertigo/qemu -C i386-softmmu V="1"
>      TARGET_DIR="i386-softmmu/" all
>      make[1]: Entering directory `/home/ssp/vertigo/qemu/i386-softmmu'
>      gcc -I/home/ssp/vertigo/qemu/slirp -I. -I/home/ssp/vertigo/qemu
>      -I/home/ssp/vertigo/qemu/fpu -I/home/ssp/vertigo/qemu/libcacard
>      -I/home/ssp/vertigo/qemu/linux-headers -I/home/ssp/vertigo/qemu/tcg
>      -I/home/ssp/vertigo/qemu/tcg/i386  -Werror -fPIE -DPIE -m64
>      -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
>      -Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings
>      -Wmissing-prototypes -fno-strict-aliasing  -fstack-protector-all
>      -Wendif-labels -Wmissing-include-dirs -Wempty-body -Wnested-externs
>      -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers
>      -Wold-style-declaration -Wold-style-definition -Wtype-limits
>      -I/usr/include/libpng12   -I/usr/include/spice-server
>      -I/usr/include/pixman-1 -I/usr/include/spice-1   -I/usr/include/nss3
>      -I/usr/include/nspr4   -pthread -I/usr/include/glib-2.0
>      -I/usr/lib64/glib-2.0/include   -DHAS_AUDIO -DHAS_AUDIO_CHOICE
>      -DTARGET_PHYS_ADDR_BITS=64 -I../linux-headers
>      -I.. -I/home/ssp/vertigo/qemu/target-i386 -DNEED_CPU_H
>      -I/home/ssp/vertigo/qemu/include    -I/usr/include/libpng12   -pthread
>      -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include   -MMD -MP -MT
>      hw/vfio_pci.o -MF hw/vfio_pci.d -O2 -D_FORTIFY_SOURCE=2 -g  -c -o
>      hw/vfio_pci.o /home/ssp/vertigo/qemu/hw/vfio_pci.c
>      cc1: warnings being treated as errors
>      /home/ssp/vertigo/qemu/hw/vfio_pci.c: In function ‘vfio_bar_write’:
>      /home/ssp/vertigo/qemu/hw/vfio_pci.c:604:84: error: value computed is not used
>      /home/ssp/vertigo/qemu/hw/vfio_pci.c: In function ‘vfio_bar_read’:
>      /home/ssp/vertigo/qemu/hw/vfio_pci.c:644:84: error: value computed is
>      not used
>      make[1]: *** [hw/vfio_pci.o] Error 1
>      make[1]: Leaving directory `/home/ssp/vertigo/qemu/i386-softmmu'
>      make: *** [subdir-i386-softmmu] Error 2

That's strange.

The lines which cause compiler errors look like this:

     vfio_eoi(DO_UPCAST(VFIODevice, bars[bar->nr], bar));

There are more uses of DO_UPCAST without any compiler error:

     VFIODevice *vdev = DO_UPCAST(VFIODevice, pdev, pdev);

Neither of both lines creates a compiler error with any of my
compilers (gcc 4.4 up to latest gcc, Linux and MinGW hosts).

When I compile with gcc option -save-temps, I get this code
for the first line:

     vfio_eoi(( __extension__ ( { char __attribute__((unused)) 
offset_must_be_zero[ -__builtin_offsetof (VFIODevice, bars[bar->nr])]; 
({ const typeof(((VFIODevice *) 0)->bars[bar->nr]) *__mptr = (bar); 
(VFIODevice *) ((char *) __mptr - __builtin_offsetof (VFIODevice, 
bars[bar->nr]));});})));

Could you please replace the first line by that code and try your compiler?
If it remains silent, I suspect a bad offsetof macro.

Do you compile on Linux? Which distribution or which C library do you use?

Regards

Stefan Weil