| Message ID | 1314564200-6872-2-git-send-email-weil@mail.berlios.de |
|---|---|
| State | Superseded |
| Headers | show |
Am 28.08.2011 um 22:43 schrieb Stefan Weil: > A packed struct needs different gcc attributes for compilations > with MinGW compilers because glib-2.0 adds compiler flag > -mms-bitfields which modifies the packing algorithm. Is that algorithm actually needed anywhere? If not, is there no GCC option to fix this centrally in configure for win32 only? Andreas > Attribute gcc_struct reverses the negative effects of -mms-bitfields. > QEMU_PACKED sets this attribute and must be used for any packed > struct which is affected by -mms-bitfields. > > Signed-off-by: Stefan Weil <weil@mail.berlios.de> > --- > compiler.h | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > diff --git a/compiler.h b/compiler.h > index 9af5dc6..a2d5959 100644 > --- a/compiler.h > +++ b/compiler.h > @@ -12,6 +12,12 @@ > #define QEMU_WARN_UNUSED_RESULT > #endif > > +#if defined(_WIN32) > +# define QEMU_PACKED __attribute__((gcc_struct, packed)) > +#else > +# define QEMU_PACKED __attribute__((packed)) > +#endif > + > #define QEMU_BUILD_BUG_ON(x) \ > typedef char qemu_build_bug_on__##__LINE__[(x)?-1:1]; > > -- > 1.7.0.4 > >
Am 28.08.2011 22:47, schrieb Andreas Färber: > Am 28.08.2011 um 22:43 schrieb Stefan Weil: > >> A packed struct needs different gcc attributes for compilations >> with MinGW compilers because glib-2.0 adds compiler flag >> -mms-bitfields which modifies the packing algorithm. > > Is that algorithm actually needed anywhere? If not, is there no GCC > option to fix this centrally in configure for win32 only? > > Andreas I think it is needed: glib-2.0 requires -mms-bitfields for MinGW which breaks networking (and more) for w32 hosts because of changes in struct alignment. A central solution would require removal of -mms-bitfields or its effects. This is possible, but very risky, because it will raise problems with glib-2.0 and w32 libraries. Therefore a central solution was rejected. See this thread: http://lists.gnu.org/archive/html/qemu-devel/2011-08/msg01877.html Stefan
On Sun, Aug 28, 2011 at 8:43 PM, Stefan Weil <weil@mail.berlios.de> wrote: > A packed struct needs different gcc attributes for compilations > with MinGW compilers because glib-2.0 adds compiler flag > -mms-bitfields which modifies the packing algorithm. > > Attribute gcc_struct reverses the negative effects of -mms-bitfields. > QEMU_PACKED sets this attribute and must be used for any packed > struct which is affected by -mms-bitfields. > > Signed-off-by: Stefan Weil <weil@mail.berlios.de> > --- > compiler.h | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > diff --git a/compiler.h b/compiler.h > index 9af5dc6..a2d5959 100644 > --- a/compiler.h > +++ b/compiler.h > @@ -12,6 +12,12 @@ > #define QEMU_WARN_UNUSED_RESULT > #endif > > +#if defined(_WIN32) > +# define QEMU_PACKED __attribute__((gcc_struct, packed)) Maybe we could also use gcc_struct also for non-win32? > +#else > +# define QEMU_PACKED __attribute__((packed)) > +#endif > + > #define QEMU_BUILD_BUG_ON(x) \ > typedef char qemu_build_bug_on__##__LINE__[(x)?-1:1]; > > -- > 1.7.0.4 > > >
On 08/30/2011 07:57 PM, Blue Swirl wrote: >> > >> > +#if defined(_WIN32) >> > +# define QEMU_PACKED __attribute__((gcc_struct, packed)) > Maybe we could also use gcc_struct also for non-win32? > >> > +#else >> > +# define QEMU_PACKED __attribute__((packed)) >> > +#endif Indeed. Paolo
Am 30.08.2011 20:29, schrieb Paolo Bonzini: > On 08/30/2011 07:57 PM, Blue Swirl wrote: >>> > >>> > +#if defined(_WIN32) >>> > +# define QEMU_PACKED __attribute__((gcc_struct, packed)) >> Maybe we could also use gcc_struct also for non-win32? >> >>> > +#else >>> > +# define QEMU_PACKED __attribute__((packed)) >>> > +#endif > > Indeed. > > Paolo > No. Extract from gcc documentation: "Two attributes are currently defined for i386 configurations: |ms_struct| and |gcc_struct" For non i386 configuration, these configurations are undefined: mipsel-linux-gnu-gcc -c -Wall test.c test.c:3: warning: ‘gcc_struct’ attribute directive ignored Therefore, we cannot use gcc_struct for most supported hosts. Linux i386 or x86_64 would support it, but they don't need it... We need one #if ... #else ... #endif to avoid 250 of them :-) Stefan |
diff --git a/compiler.h b/compiler.h index 9af5dc6..a2d5959 100644 --- a/compiler.h +++ b/compiler.h @@ -12,6 +12,12 @@ #define QEMU_WARN_UNUSED_RESULT #endif +#if defined(_WIN32) +# define QEMU_PACKED __attribute__((gcc_struct, packed)) +#else +# define QEMU_PACKED __attribute__((packed)) +#endif + #define QEMU_BUILD_BUG_ON(x) \ typedef char qemu_build_bug_on__##__LINE__[(x)?-1:1];
A packed struct needs different gcc attributes for compilations with MinGW compilers because glib-2.0 adds compiler flag -mms-bitfields which modifies the packing algorithm. Attribute gcc_struct reverses the negative effects of -mms-bitfields. QEMU_PACKED sets this attribute and must be used for any packed struct which is affected by -mms-bitfields. Signed-off-by: Stefan Weil <weil@mail.berlios.de> --- compiler.h | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-)