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Re: [PATCH] Config.mk: drop -Wdeclaration-after-statement


  • To: Alexander Kanavin <alex@xxxxxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 29 Nov 2023 08:51:11 +0100
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  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 29 Nov 2023 07:51:36 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 28.11.2023 18:47, Alexander Kanavin wrote:
> Such constructs are fully allowed by C99:
> https://gcc.gnu.org/onlinedocs/gcc-12.2.0/gcc/Mixed-Labels-and-Declarations.html#Mixed-Labels-and-Declarations

There's more to this: It may also be a policy of ours (or of any sub-component)
to demand that declarations and statements are properly separated. This would
therefore need discussing first.

> If the flag is present, then building against python 3.12 will fail thusly:
> 
> | 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

At least by the specific wording of the diagnostic I'm inclined to call this
a compiler bug: There's no point in mentioning C90 when -std=gnu99 was passed.

> --- a/Config.mk
> +++ b/Config.mk
> @@ -177,8 +177,6 @@ CFLAGS += -std=gnu99

Just up from here there is

CFLAGS += -std=gnu99

Yet there's no

HOSTCFLAGS += -std=gnu99

anywhere. Hence ...

>  CFLAGS += -Wall -Wstrict-prototypes
>  
> -$(call cc-option-add,HOSTCFLAGS,HOSTCC,-Wdeclaration-after-statement)

... imo this removal is inappropriate.

Jan

> -$(call cc-option-add,CFLAGS,CC,-Wdeclaration-after-statement)
>  $(call cc-option-add,CFLAGS,CC,-Wno-unused-but-set-variable)
>  $(call cc-option-add,CFLAGS,CC,-Wno-unused-local-typedefs)
>  




 


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