Exception/instruction barrier

[Hendrik Greving]

Yes it would.  But some instructions following these semantics also
have output operands, and this not supported afaik.

On Sat, Aug 31, 2013 at 4:16 AM, Rob <robpilling@gmail.com> wrote:
> On Fri, Aug 30, 2013 at 10:41:47AM -0700, Hendrik Greving wrote:
>> Following problem: Below, the instruction
>> my_insn_can_jump_to_coolLabel is an instruction that can raise a
>> fault, that is subsequently handled by a higher OS like code, that
>> then will always jump to B3. I believe similar stuff exists in the
>> Linux kernel. What happens is that some code from B3 gets hoisted to
>> B1' (some base address from a complex address in B3, I suspect CSE).
>> The base address is then missing in case we 'jump' to B3 if an
>> exception had been raised.
>>
> ...
>>
>> Is there anything like instruction barriers I can somehow support at
>> codeLabel maybe? How does the Linux kernel do this (if so)?
>
> Will asm goto() help here? gcc assumes asm statements don't affect
> program flow when it reorders basic blocks. You should use asm goto()
> with a list of labels at the end if your asm statement will jump around.
>
> Or alternatively you could give gcc -fno-reorder-blocks to stop it
> shifting code around.
>
> Thanks,
> Rob