Re: [Qemu-devel] Undefined reference to 'ffs' when building for win64

[Andreas Färber]

Am 15.02.2013 22:16, schrieb Stefan Weil:
> Am 15.02.2013 20:40, schrieb Andreas Färber:
>> Am 15.02.2013 19:29, schrieb Jacob Kroon:
>>> On Fri, Feb 15, 2013 at 7:03 PM, Andreas Färber <address@hidden> wrote:
>>>> Am 06.02.2013 14:12, schrieb Jacob Kroon:
>>>>> I'm trying to cross-build qemu for win64 on a Fedora 18/x86_64 system,
>>>>> using all the necessary mingw64 packages from Fedora. Using latest
>>>>> qemu from git (5f876756c57c15f5e14d4136fc432b74f05f082b), I get an
>>>>> error when linking "qemu-img.exe":
>>>> Has this been resolved in the meantime? MinGW64 cross-build of my patch
>>>> queue works fine.
>>> I tried again with latest from git,
>>> 571f65ec20fbcb991d7bce51787248ab9d325e3f, I still get the linking
>>> errors though.
>>>
>>> The configure-script command-line I use is:
>>>
>>> ./configure --cross-prefix=x86_64-w64-mingw32- --disable-guest-agent
>>> --disable-vnc --disable-werror --enable-debug
>>> --target-list=i386-softmmu
>>>
>>> I'm on a Fedora 18 system, updated with latest packages.
>> Okay, so I can reproduce it now by adding --enable-debug:
>> .../configure --cross-prefix=x86_64-w64-mingw32- --enable-debug
>>
>>   LINK  arm-softmmu/qemu-system-armw.exe
>> ../block.o: In function `bdrv_set_dirty_tracking':
>> /home/andreas/QEMU/qemu-cpu/block.c:4316: undefined reference to `ffs'
>> ../block/qcow2.o: In function `qcow2_create2':
>> /home/andreas/QEMU/qemu-cpu/block/qcow2.c:1184: undefined reference to `ffs'
>> ../block/qed.o: In function `bdrv_qed_open':
>> /home/andreas/QEMU/qemu-cpu/block/qed.c:429: undefined reference to `ffs'
>> /home/andreas/QEMU/qemu-cpu/block/qed.c:431: undefined reference to `ffs'
>> ../hw/bt-sdp.o: In function `sdp_service_record_build':
>> /home/andreas/QEMU/qemu-cpu/hw/bt-sdp.c:710: undefined reference to `ffs'
>> ../hw/max7310.o:/home/andreas/QEMU/qemu-cpu/hw/max7310.c:94: more
>> undefined references to `ffs' follow
>> collect2: error: ld returned 1 exit status
>> make[1]: *** [qemu-system-armw.exe] Fehler 1
>> make: *** [subdir-arm-softmmu] Fehler 2
>>
>> Jacob, for now just drop --enable-debug from your command line or try
>> tweaking --extra-cflags with some higher -O optimization option.
>>
>> Paolo, Stefan, any ideas how to fix?
>>
>> Andreas
> 
> 
> Hi Jacob,
> 
> earlier versions of QEMU provided an implementation of ffs()
> because it was needed for w32 compilations without optimisation.
> 
> Later w32 used libiberty.a which provides ffs(). w64 never needed
> the ffs() implementation, so I removed it in commit
> 57a8821bc6e4457230075a5c8da5f8a083889686.
> 
> In my builds (w32 and w64, Debian / Ubuntu Linux cross and native)
> I don't get an unresolvedsymbol ffs.
> 
> It looks like most (but not all) versions of gcc emit built-in code
> for ffs() even for compilations without optimisation. I have to provide
> additional compiler options (e.g. -fno-builtin-ffs) to get a real
> function call.
> Only then I get the linker errors which you see.
> 
> Obviously your compiler behaves different (or did you add extra
> compiler options?).
> 
> Try this short test.c code:
> 
> int ffs(unsigned n);
> int main(int argc, char *argv[])
> {
>   return ffs(argc);
> }
> 
> On Debian, I compiled and tested like this:
> 
> amd64-mingw32msvc-gcc -c -g -O0 test.c
> amd64-mingw32msvc-nm test.o
> 
> There is no ffs function call in the resulting binary.
> 
> If your compiler creates a function call, we have to know
> why and whether there is a simple rule which versions of
> gcc behave like that. If there is no simple rule, we need
> a configure check.

$ x86_64-w64-mingw32-gcc --version
x86_64-w64-mingw32-gcc (GCC) 4.7.2
Copyright (C) 2012 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.
$ x86_64-w64-mingw32-gcc -c -g -O0 test_ffs.c
$ x86_64-w64-mingw32-nm test_ffs.o
0000000000000000 b .bss
0000000000000000 d .data
0000000000000000 N .debug_abbrev
0000000000000000 N .debug_aranges
0000000000000000 N .debug_frame
0000000000000000 N .debug_info
0000000000000000 N .debug_line
0000000000000000 N .debug_loc
0000000000000000 p .pdata
0000000000000000 t .text
0000000000000000 r .xdata
                 U __main
                 U ffs
0000000000000000 T main

https://build.opensuse.org/package/show?package=mingw64-cross-gcc&project=windows%3Amingw%3Awin64

Regards,
Andreas

-- 
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg