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SubjectRe: [PATCH 1/3] retpolines: Only enable retpoline when compiler support it
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On 2018/10/30 18:09, Peter Zijlstra wrote:
> On Tue, Oct 30, 2018 at 06:39:24PM +0900, Masahiro Yamada wrote:
>> Hi,
>>
>>
>>
>> On Tue, Oct 30, 2018 at 3:57 PM Zhenzhong Duan
>> <zhenzhong.duan@oracle.com> wrote:
>>>
>>> Since retpoline capable compilers are widely available, make
>>> CONFIG_RETPOLINE hard depend on it.
>>>
>>> Change KBUILD to use CONFIG_RETPOLINE_SUPPORT to avoid conflict with
>>> CONFIG_RETPOLINE which is used by kernel.
>>>
>>> With all that stuff, the check of RETPOLINE is changed to
>>> CONFIG_RETPOLINE.
>>>
>>> This change is based on suggestion in https://lkml.org/lkml/2018/9/18/1016
>>>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
>>> Cc: Thomas Gleixner <tglx@linutronix.de>
>>> Cc: Peter Zijlstra <peterz@infradead.org>
>>> Cc: Borislav Petkov <bp@suse.de>
>>> Cc: Daniel Borkmann <daniel@iogearbox.net>
>>> Cc: David Woodhouse <dwmw@amazon.co.uk>
>>> Cc: H. Peter Anvin <hpa@zytor.com>
>>> Cc: Ingo Molnar <mingo@redhat.com>
>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>> Cc: Andy Lutomirski <luto@kernel.org>
>>> Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
>>> Cc: Michal Marek <michal.lkml@markovi.net>
>>> ---
>>
>>
>> Instead of adding another CONFIG option,
>> does it make sense to add compiler support checks
>> to 'depends on' syntax ?
>>
>>
>> config RETPOLINE
>> bool "Avoid speculative indirect branches in kernel"
>> depends on $(cc-option,-mindirect-branch=thunk-extern
>> -mindirect-branch-register) || \
>> $(cc-option,-mretpoline-external-thunk)
>> default y
>> select STACK_VALIDATION if HAVE_STACK_VALIDATION

Looks better, thanks for suggestion.

>
> That seems to be what we did for stackprotector, which is similar in
> that it used to fail the build. So yes, this seems sane.

Should I add a scripts/gcc-x86_64-has-retpoline.sh like what
stackprotector does as below or there is a simpler way?

config CC_HAS_SANE_STACKPROTECTOR
bool
default
$(success,$(srctree)/scripts/gcc-x86_64-has-stack-protector.sh $(CC)) if
64BIT
default
$(success,$(srctree)/scripts/gcc-x86_32-has-stack-protector.sh $(CC))
help
We have to make sure stack protector is unconditionally
disabled if
the compiler produces broken code.

Thanks
Zhenzhong

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