Re: [XEN PATCH] xen/build: introduce CLANG_FLAGS for testing other CFLAGS

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 29/05/2020 16:43, Anthony PERARD wrote:
> Commit 534519f0514f ("xen: Have Kconfig check $(CC)'s version")
> introduced the use of CLANG_FLAGS in Kconfig which is used when
> testing for other CFLAGS via $(cc-option ...) but CLANG_FLAGS doesn't
> exist in the Xen build system. (It's a Linux/Kbuild variable that
> haven't been added yet.)
>
> The missing CLANG_FLAGS isn't an issue for $(cc-option ..) but it
> would be when $(as-instr ..) gets imported from Kbuild to tests
> assembly instruction. We need to know if we are going to use clang's
> assembler or not.
>
> CLANG_FLAGS needs to be calculated before we call Kconfig.
>
> So, this patch adds CLANG_FLAGS which may contain two flags which are
> needed for further testing of $(CC)'s capabilities:
>   -no-integrated-as
>     This flags isn't new, but simply tested earlier so that it can be
>     used in Kconfig. The flags is only added for x86 builds like
>     before.
>   -Werror=unknown-warning-option
>     The one is new and is to make sure that the warning is enabled,
>     even though it is by default but could be disabled in a particular
>     build of clang, see Linux's commit e8de12fb7cde ("kbuild: Check
>     for unknown options with cc-option usage in Kconfig and clang")
>
>     It is present in clang 3.0.0, according Linux's commit
>     589834b3a009 ("kbuild: Add -Werror=unknown-warning-option to
>     CLANG_FLAGS").
>
> (The "note" that say that the flags was only added once wasn't true
> when tested on CentOS 6, so the patch uses $(or) and the flag will only
> be added once.)
>
> Fixes: 534519f0514f ("xen: Have Kconfig check $(CC)'s version")
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>