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Re: [PATCH v2] Kbuild: use -fshort-wchar globally

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  Re: [PATCH v2] Kbuild: use -fshort-wchar globally Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-08-20 14:40 +0200
    Re: [PATCH v2] Kbuild: use -fshort-wchar globally Arnd Bergmann <arnd@arndb.de> - 2017-08-20 21:30 +0200
      Re: [PATCH v2] Kbuild: use -fshort-wchar globally Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-08-21 02:20 +0200

#1715931 — Re: [PATCH v2] Kbuild: use -fshort-wchar globally

Hi Arnd,

This patch was picked up for linux-next
(I assume it was queued up for 4.14-rc1)
but I see this warning in Linus' tree.

If we are not comfortable with this warning in the 4.13 release,
shall I include this patch in the kbuild/fixes pull request?
(planned this week)

Please let me know your thought.


2017-07-26 22:36 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
> A previous patch added the --no-wchar-size-warning to the Makefile to
> avoid this harmless warning:

"A previous patch" sounds ambiguous.

The previous patch was applied one year ago.


If it is OK, I can reword like

Commit 971a69db7dc0 ("Xen: don't warn about 2-byte wchar_t in efi") added ...






> arm-linux-gnueabi-ld: warning: drivers/xen/efi.o uses 2-byte wchar_t yet the output is to use 4-byte wchar_t; use of wchar_t values across objects may fail
>
> Changing kbuild to use thin archives instead of recursive linking
> unfortunately brings the same warning back during the final link.
>
> The kernel does not use wchar_t string literals at this point, and
> xen does not use wchar_t at all (only efi_char16_t), so the flag
> has no effect, but as pointed out by Jan Beulich, adding a wchar_t
> string literal would be bad here.
>
> Since wchar_t is always defined as u16, independent of the toolchain
> default, always passing -fshort-wchar is correct and lets us
> remove the Xen specific hack along with fixing the warning.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Fixes: 971a69db7dc0 ("Xen: don't warn about 2-byte wchar_t in efi")
> Acked-by: David Vrabel <david.vrabel@citrix.com>
> Link: https://patchwork.kernel.org/patch/9275217/
> ---
> I submitted an earlier patch in August 2016, simply removing the
> flag in xen, but there seems to be no harm in enabling it globally
> ---
>  Makefile             | 2 +-
>  drivers/xen/Makefile | 3 ---
>  2 files changed, 1 insertion(+), 4 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index f1533423094f..0fe63a47fd52 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -396,7 +396,7 @@ LINUXINCLUDE    := \
>  KBUILD_CPPFLAGS := -D__KERNEL__
>
>  KBUILD_CFLAGS   := -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
> -                  -fno-strict-aliasing -fno-common \
> +                  -fno-strict-aliasing -fno-common -fshort-wchar \
>                    -Werror-implicit-function-declaration \
>                    -Wno-format-security \
>                    -std=gnu89 $(call cc-option,-fno-PIE)
> diff --git a/drivers/xen/Makefile b/drivers/xen/Makefile
> index 8feab810aed9..7f188b8d0c67 100644
> --- a/drivers/xen/Makefile
> +++ b/drivers/xen/Makefile
> @@ -7,9 +7,6 @@ obj-y   += xenbus/
>  nostackp := $(call cc-option, -fno-stack-protector)
>  CFLAGS_features.o                      := $(nostackp)
>
> -CFLAGS_efi.o                           += -fshort-wchar
> -LDFLAGS                                        += $(call ld-option, --no-wchar-size-warning)
> -
>  dom0-$(CONFIG_ARM64) += arm-device.o
>  dom0-$(CONFIG_PCI) += pci.o
>  dom0-$(CONFIG_USB_SUPPORT) += dbgp.o
> --
> 2.9.0
>



-- 
Best Regards
Masahiro Yamada

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#1716008

On Sun, Aug 20, 2017 at 2:31 PM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> Hi Arnd,
>
> This patch was picked up for linux-next
> (I assume it was queued up for 4.14-rc1)
> but I see this warning in Linus' tree.
>
> If we are not comfortable with this warning in the 4.13 release,
> shall I include this patch in the kbuild/fixes pull request?
> (planned this week)
>
> Please let me know your thought.

Yes, I think it would be good to have in 4.13, since it's a regression
against older kernels.

> 2017-07-26 22:36 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
>> A previous patch added the --no-wchar-size-warning to the Makefile to
>> avoid this harmless warning:
>
> "A previous patch" sounds ambiguous.
>
> The previous patch was applied one year ago.
>
>
> If it is OK, I can reword like
>
> Commit 971a69db7dc0 ("Xen: don't warn about 2-byte wchar_t in efi") added ...

Good idea, thanks!

       Arnd

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#1716048

2017-08-21 4:22 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
> On Sun, Aug 20, 2017 at 2:31 PM, Masahiro Yamada
> <yamada.masahiro@socionext.com> wrote:
>> Hi Arnd,
>>
>> This patch was picked up for linux-next
>> (I assume it was queued up for 4.14-rc1)
>> but I see this warning in Linus' tree.
>>
>> If we are not comfortable with this warning in the 4.13 release,
>> shall I include this patch in the kbuild/fixes pull request?
>> (planned this week)
>>
>> Please let me know your thought.
>
> Yes, I think it would be good to have in 4.13, since it's a regression
> against older kernels.
>
>> 2017-07-26 22:36 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
>>> A previous patch added the --no-wchar-size-warning to the Makefile to
>>> avoid this harmless warning:
>>
>> "A previous patch" sounds ambiguous.
>>
>> The previous patch was applied one year ago.
>>
>>
>> If it is OK, I can reword like
>>
>> Commit 971a69db7dc0 ("Xen: don't warn about 2-byte wchar_t in efi") added ...
>
> Good idea, thanks!
>


Applied to linux-kbuild/fixes.  Thanks!



-- 
Best Regards
Masahiro Yamada

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