Re: Re: [PATCH v3 1/7] riscv: ftrace: support fastcc in Clang for WITH_ARGS

Evgenii Shatokhin
2024-12-03T14:44:45Z

Hi,

On 03.12.2024 15:05, Björn Töpel wrote:
>
> Andy Chiu <andybnac@gmail.com> writes:
>
>> From: Andy Chiu <andy.chiu@sifive.com>
>>
>> Some caller-saved registers which are not defined as function arguments
>> in the ABI can still be passed as arguments when the kernel is compiled
>> with Clang. As a result, we must save and restore those registers to
>> prevent ftrace from clobbering them.
>>
>> - [1]: https://reviews.llvm.org/D68559
>>
>> Reported-by: Evgenii Shatokhin <e.shatokhin@yadro.com>
>> Closes: https://lore.kernel.org/linux-riscv/7e7c7914-445d-426d-89a0-59a9199c45b1@yadro.com/
>> Acked-by: Nathan Chancellor <nathan@kernel.org>
>> Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
>
> Fixes tag?

As far as I understand it, Ftrace for RISC-V has had this problem since
support for FTRACE_WITH_REGS was added. FTRACE_WITH_ARGS inherited it.

So, it should probably be as follows:

Fixes: aea4c671fb98 ("riscv/ftrace: Add DYNAMIC_FTRACE_WITH_REGS support")

It is more of a workaround rather than a fix though, because it is still
undecided where the problem is, in the kernel or in LLVM/clang. That
discussion went nowhere, unfortunately, so it is better to use a
workaround and move on, IMO.

>
> Reviewed-by: Björn Töpel <bjorn@rivosinc.com>
>

Regards,
Evgenii