sbcl-help

[Sbcl-help] Prevent register clobbering

[Leslie P. P. <sk...@vi...>]

I'm writing a function to interrupt a thread and take a
look at the current state of its registers.

I will use VOPs to store the register values into a known
memory location. This in itself works fine.

The problem is that a full call as in

  (interrupt-thread thread #'save-regs)

clobbers at least part of the registers (e.g. function
in EAX on x86).

I've considered using a signal handler instead of
INTERRUPT-THREAD but I'm unsure whether that will
do the job since a handler installed with
ENABLE-INTERRUPT will be run in an APPLY inside an
FLET.

Before I spent more time digging: is there a smart way
to have a direct jump to the function entry point
preventing any reg modifications?

Alternatively, can I instruct the compiler to push the
old state of the registers onto the stack?

  Leslie

-- 
http://www.linkedin.com/in/polzer

Re: [Sbcl-help] Prevent register clobbering

[Gábor M. <me...@re...>]

On Lunes 06 Julio 2009, Leslie P. Polzer wrote:
> I'm writing a function to interrupt a thread and take a
> look at the current state of its registers.
>
> I will use VOPs to store the register values into a known
> memory location. This in itself works fine.
>
> The problem is that a full call as in
>
>   (interrupt-thread thread #'save-regs)
>
> clobbers at least part of the registers (e.g. function
> in EAX on x86).
>
> I've considered using a signal handler instead of
> INTERRUPT-THREAD but I'm unsure whether that will
> do the job since a handler installed with
> ENABLE-INTERRUPT will be run in an APPLY inside an
> FLET.
>
> Before I spent more time digging: is there a smart way
> to have a direct jump to the function entry point
> preventing any reg modifications?
>
> Alternatively, can I instruct the compiler to push the
> old state of the registers onto the stack?
>
>   Leslie

Even a C signal handler will have some registers clobbered. The 
interrupt context is already stored, see interrupt_contexts in 
src/runtime/genesis/thread.h. It's of type os_context and is platform 
specific.

Cheers, Gabor