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

[Masahiro Yamada]

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@xxxxxxxx>:
> 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@xxxxxxxx>
> Fixes: 971a69db7dc0 ("Xen: don't warn about 2-byte wchar_t in efi")
> Acked-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> 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