Re: [Qemu-devel] [PATCH] windows build: -lssp added to qga-vss.dll libraries list

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/03/2015 20:59, Stefan Weil wrote:
> Am 11.03.2015 um 18:10 schrieb Joseph Hindin:
>> When building qga-bss.dll with 64-bit mingw toolchain v. 4.9.2, the
> 
> Typo: qga-vss.dll
> 
>> qga-vss.dll linking fails with unresolved symbols from libssp,
>> stack protection support, like the following message:
>>
>> .../qga/vss-win32/install.cpp:52: undefined reference to
>> `__stack_chk_fail'
>>
>> The patch fixes the problem by adding libssp to the qga-vss.dll
>> libraries list.
>>
>> Signed-off-by: Joseph Hindin <jhindin@daynix.com>
>> ---
>>   qga/vss-win32/Makefile.objs | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/qga/vss-win32/Makefile.objs b/qga/vss-win32/Makefile.objs
>> index 6a69d50..bd0840d 100644
>> --- a/qga/vss-win32/Makefile.objs
>> +++ b/qga/vss-win32/Makefile.objs
>> @@ -5,7 +5,7 @@ qga-vss-dll-obj-y += requester.o provider.o install.o
>>   obj-qga-vss-dll-obj-y = $(addprefix $(obj)/, $(qga-vss-dll-obj-y))
>>   $(obj-qga-vss-dll-obj-y): QEMU_CXXFLAGS = $(filter-out
>> -Wstrict-prototypes -Wmissing-prototypes -Wnested-externs
>> -Wold-style-declaration -Wold-style-definition -Wredundant-decls
>> -fstack-protector-all, $(QEMU_CFLAGS)) -Wno-unknown-pragmas
>> -Wno-delete-non-virtual-dtor
>>   -$(obj)/qga-vss.dll: LDFLAGS = -shared
>> -Wl,--add-stdcall-alias,--enable-stdcall-fixup -lole32 -loleaut32
>> -lshlwapi -luuid -static
>> +$(obj)/qga-vss.dll: LDFLAGS = -shared
>> -Wl,--add-stdcall-alias,--enable-stdcall-fixup -lole32 -loleaut32
>> -lshlwapi -luuid -lssp -static
>>   $(obj)/qga-vss.dll: $(obj-qga-vss-dll-obj-y)
>> $(SRC_PATH)/$(obj)/qga-vss.def
>>       $(call quiet-command,$(CXX) -o $@ $(qga-vss-dll-obj-y)
>> $(SRC_PATH)/qga/vss-win32/qga-vss.def $(CXXFLAGS) $(LDFLAGS),"  LINK 
>> $(TARGET_DIR)$@")
>>   
> 
> Adding -lssp works, but adding -fstack-protector-all to the linker flags
> also works and might be the better solution.
> 
> -$(obj)/qga-vss.dll: LDFLAGS = -shared
> -Wl,--add-stdcall-alias,--enable-stdcall-fixup -lole32 -loleaut32
> -lshlwapi -luuid -static
> +$(obj)/qga-vss.dll: LDFLAGS = -fstack-protector-all -shared
> -Wl,--add-stdcall-alias,--enable-stdcall-fixup -lole32 -loleaut32
> -lshlwapi -luuid -static
> 
> Could you please try that and send an updated patch? Please cc it also
> to qemu-trivial.

Actually it's not trivial...

There is already an attempt to avoid the stack protector in
qga/vss-win32/Makefile.objs:

$(obj-qga-vss-dll-obj-y): QEMU_CXXFLAGS = $(filter-out -Wstrict-prototypes \
    -Wmissing-prototypes -Wnested-externs -Wold-style-declaration \
    -Wold-style-definition -Wredundant-decls -fstack-protector-all, \
    $(QEMU_CFLAGS)) -Wno-unknown-pragmas -Wno-delete-non-virtual-dtor

Perhaps you're using -fstack-protector-strong, and so the above line
should use "-fstack-protector%"?

Instead, if using the stack protector is fine, -fstack-protector-all
should not be filtered out in the above line.

In that case, I agree with Stefan that using -f is cleaner than -lssp,
but it's even cleaner to make the flags match (i.e. it's unclean to
have -fstack-protector-strong in the CFLAGS and -fstack-protector-all
in the LDFLAGS).  So I'd do something like this to get the right flag:

diff --git a/configure b/configure
index 7ba4bcb..0e84b22 100755
--- a/configure
+++ b/configure
@@ -1510,6 +1510,7 @@ if test "$stack_protector" != "no"; then
     # setups fail only on a .c->.o compile and some only at link time
     if do_cc $QEMU_CFLAGS -Werror $flag -c -o $TMPO $TMPC &&
        compile_prog "-Werror $flag" ""; then
+      stack_protector=$flag
       QEMU_CFLAGS="$QEMU_CFLAGS $flag"
       LIBTOOLFLAGS="$LIBTOOLFLAGS -Wc,$flag"
       sp_on=1
@@ -5003,6 +5004,7 @@ echo "LDFLAGS_NOPIE=$LDFLAGS_NOPIE" >> $config_host_mak
 echo "LIBTOOLFLAGS=$LIBTOOLFLAGS" >> $config_host_mak
 echo "LIBS+=$LIBS" >> $config_host_mak
 echo "LIBS_TOOLS+=$libs_tools" >> $config_host_mak
+echo "STACK_PROTECTOR_FLAG=$stack_protector" >> $config_host_mak
 echo "EXESUF=$EXESUF" >> $config_host_mak
 echo "DSOSUF=$DSOSUF" >> $config_host_mak
 echo "LDFLAGS_SHARED=$LDFLAGS_SHARED" >> $config_host_mak


and then use it in qga/vss-win32/Makefile.objs.

Thanks,

Paolo