Exception/instruction barrier

Rob robpilling@gmail.com
Sat Aug 31 16:32:00 GMT 2013

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.


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