Re: [Qemu-devel] [PATCH v2] configure: Force the C standard to gnu99

[Thomas Huth <thuth@redhat.com>]

On 2019-01-09 15:31, Daniel P. Berrangé wrote:
> On Wed, Jan 09, 2019 at 03:24:29PM +0100, Thomas Huth wrote:
>> Different versions of GCC and Clang use different versions of the C standard.
>> This repeatedly caused problems already, e.g. with duplicated typedefs:
>>
>>  https://lists.gnu.org/archive/html/qemu-devel/2018-11/msg05829.html
>>
>> or with for-loop variable initializers:
>>
>>  https://lists.gnu.org/archive/html/qemu-devel/2019-01/msg00237.html
>>
>> To avoid these problems, we should enforce the C language version to the
>> same level for all compilers. Since our minimum compiler versions is
>> GCC v4.8, our best option is "gnu99" right now ("gnu17" is not available
>> there yet, and "gnu11" is marked as "experimental").
>>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>  v2: Use gnu99 instead of gnu11
>>
>>  configure | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> 
>> diff --git a/configure b/configure
>> index b9f34af..721ade7 100755
>> --- a/configure
>> +++ b/configure
>> @@ -105,7 +105,8 @@ update_cxxflags() {
>>      for arg in $QEMU_CFLAGS; do
>>          case $arg in
>>              -Wstrict-prototypes|-Wmissing-prototypes|-Wnested-externs|\
>> -            -Wold-style-declaration|-Wold-style-definition|-Wredundant-decls)
>> +            -Wold-style-declaration|-Wold-style-definition|-Wredundant-decls|\
>> +            -std=gnu99)
> 
> IIUC this is to  drop  -std=gnu99 from CXXFLAGS, so C++ code (only the
> guest-agent on Win32 IIUC) will use the compiler default still.

We also use it for the capstone disassembler and disas/libvixl.

> We could consider also setting a suitable -std for CXXFLAGS too in future
> though...

Shall I send a v3 with "-std=gnu++98" (which seems to be the only usable
option right now), or shall we wait until we really hit a problem with
the C++ code?

 Thomas