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

[Jacob Kroon]

Hi Stefan,

[...]

On Fri, Feb 15, 2013 at 10:16 PM, Stefan Weil <address@hidden> wrote:
>
> 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?).

Version information about the compiler I'm using is listed below:

address@hidden flexemu]$ i686-w64-mingw32-gcc -v
Using built-in specs.
COLLECT_GCC=i686-w64-mingw32-gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/i686-w64-mingw32/4.7.2/lto-wrapper
Target: i686-w64-mingw32
Configured with: ../configure --prefix=/usr --bindir=/usr/bin
--includedir=/usr/include --libdir=/usr/lib64 --mandir=/usr/share/man
--infodir=/usr/share/info --datadir=/usr/share
--build=x86_64-redhat-linux-gnu --host=x86_64-redhat-linux-gnu
--with-gnu-as --with-gnu-ld --verbose --without-newlib
--disable-multilib --disable-plugin --with-system-zlib --disable-nls
--without-included-gettext --disable-win32-registry
--enable-languages=c,c++,objc,obj-c++,fortran
--with-bugurl=http://bugzilla.redhat.com/bugzilla --with-ppl
--disable-ppl-version-check --with-cloog --enable-libgomp
--target=i686-w64-mingw32
--with-sysroot=/usr/i686-w64-mingw32/sys-root
--with-gxx-include-dir=/usr/i686-w64-mingw32/sys-root/mingw/include/c++
Thread model: win32
gcc version 4.7.2 20120920 (Fedora MinGW 4.7.2-7.fc18) (GCC)


I'm not passing any special compiler flags that I know of. Building
for W32 gives me the
same linking errors, as Andreas pointed out it seems to the
"--enable-debug" flag that is
breaking the build for me. This is the qcow2.o compile command I get:

i686-w64-mingw32-gcc -I. -I/home/jkroon/Projects/flexemu/qemu -I/home/jkroon/Pro
jects/flexemu/qemu/include -m32 -D__USE_MINGW_ANSI_STDIO=1 -DWIN32_LEAN_AND_MEAN
 -DWINVER=0x501 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -Wstric
t-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings -Wmissing-prototype
s -fno-strict-aliasing -I/home/jkroon/Projects/flexemu/qemu/../slaves  -fstack-p
rotector-all -Wendif-labels -Wmissing-include-dirs -Wempty-body -Wnested-externs
 -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers -Wold-style-dec
laration -Wold-style-definition -Wtype-limits -I/usr/i686-w64-mingw32/sys-root/m
ingw/include/pixman-1   -Iblock -Iblock -mms-bitfields -I/usr/i686-w64-mingw32/s
ys-root/mingw/include/glib-2.0 -I/usr/i686-w64-mingw32/sys-root/mingw/lib/glib-2
.0/include   -MMD -MP -MT block/qcow2.o -MF block/qcow2.d -g  -c -o block/qcow2.
o block/qcow2.c

> 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.

Output on my laptop, not quite sure how to interpret it though.. :

address@hidden temp]$ i686-w64-mingw32-nm test.o
00000000 b .bss
00000000 d .data
00000000 N .debug_abbrev
00000000 N .debug_aranges
00000000 N .debug_frame
00000000 N .debug_info
00000000 N .debug_line
00000000 N .debug_loc
         U _ffs
00000000 T _main
         U ___main
00000000 t .text

Regards
Jacob