Re: [PATCH] Only compile the hypervisor with -Wdeclaration-after-statement

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.12.2023 19:32, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> Right now, all tools and hypervisor will be complied with the option
> -Wdeclaration-after-statement. While most of the code in the hypervisor
> is controlled by us, for tools we may import external libraries.
> 
> The build will fail if one of them are using the construct we are
> trying to prevent. This is the case when building against Python 3.12
> and Yocto:
> 
> | In file included from 
> /srv/storage/alex/yocto/build-virt/tmp/work/core2-64-poky-linux/xen-tools/4.17+stable/recipe-sysroot/usr/include/python3.12/Python.h:44,
> |                  from xen/lowlevel/xc/xc.c:8:
> | 
> /srv/storage/alex/yocto/build-virt/tmp/work/core2-64-poky-linux/xen-tools/4.17+stable/recipe-sysroot/usr/include/python3.12/object.h:
>  In function 'Py_SIZE':
> | 
> /srv/storage/alex/yocto/build-virt/tmp/work/core2-64-poky-linux/xen-tools/4.17+stable/recipe-sysroot/usr/include/python3.12/object.h:233:5:
>  error: ISO C90 forbids mixed declarations and code 
> [-Werror=declaration-after-statement]
> |   233 |     PyVarObject *var_ob = _PyVarObject_CAST(ob);
> |       |     ^~~~~~~~~~~
> | In file included from 
> /srv/storage/alex/yocto/build-virt/tmp/work/core2-64-poky-linux/xen-tools/4.17+stable/recipe-sysroot/usr/include/python3.12/Python.h:53:
> | 
> /srv/storage/alex/yocto/build-virt/tmp/work/core2-64-poky-linux/xen-tools/4.17+stable/recipe-sysroot/usr/include/python3.12/cpython/longintrepr.h:
>  In function '_PyLong_CompactValue':
> | 
> /srv/storage/alex/yocto/build-virt/tmp/work/core2-64-poky-linux/xen-tools/4.17+stable/recipe-sysroot/usr/include/python3.12/cpython/longintrepr.h:121:5:
>  error: ISO C90 forbids mixed declarations and code 
> [-Werror=declaration-after-statement]
> |   121 |     Py_ssize_t sign = 1 - (op->long_value.lv_tag & 
> _PyLong_SIGN_MASK);
> |       |     ^~~~~~~~~~
> | cc1: all warnings being treated as errors
> 
> Looking at the tools directory, a fair few directory already add
> -Wno-declaration-after-statement to inhibit the default behavior.
> 
> We have always build the hypervisor with the flag, so for now remove
> only the flag for anything but the hypervisor. We can decide at later
> time whether we want to relax.
> 
> Also remove the -Wno-declaration-after-statement in some subdirectory
> as the flag is now unnecessary.

With all these removals, don't you need to add the option centrally
somewhere? Or else are you sure that no compiler version, including
distro-customized ones, would ever come with the warning enabled by
default?

Jan