Re: [PATCH v1 4/6] bpf, core: Add weak arch_prepare_goto()

[Tiezhu Yang]

On 10/16/2024 02:36 AM, Alexei Starovoitov wrote:
> On Tue, Oct 15, 2024 at 4:50 AM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> > The objtool program needs to analysis the control flow of each
> > object file generated by compiler toolchain, it needs to know
> > all the locations that a branch instruction may jump into.

...

> > +       arch_prepare_goto();
> >         goto *jumptable[insn->code];
>
> That looks fragile. There is no guarantee that compiler will keep
> asm statement next to indirect goto.
> It has all rights to move/copy such goto around.
> There are other parts in the kernel which are not annotated either:
> drm_exec_retry_on_contention(),
> drivers/misc/lkdtm/cfi.c
>
> You're arguing that it's hard to properly in the compiler,
> but that's the only option. It has to be done by the compiler.

Thank you very much for your reply. I will drop this patch
and try to find a proper way to handle this case.

By the way, I spent more time to test and analysis with gcc
and clang on x86 and loongarch, it needs to fix some corner
issues for the other patches compiled with clang.

Anyway, I will submit v2 series without changing bpf file,
patch #4 and patch #5 will be removed.

Thanks,
Tiezhu