[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] Re: Question on implementatio of GETPC()
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: Question on implementatio of GETPC() |
Date: |
Wed, 28 Apr 2010 10:12:42 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
Jun Koi wrote:
> Hi,
>
> In x86, GETPC() is implemented as below:
>
> # define GETPC() ((void *)((unsigned long)__builtin_return_address(0) - 1))
>
> As I understand, it gets the returned address on the stack, then
> subtract 1 to get back to the above address.
>
> Imagine we have code like this (pseudo asm code):
>
> ....
> CALL <relative address>
> <next-insn>
> ....
>
> When we call GETPC, we get the address of <next-insn>, and subtract 1.
> But the problem is that the CALL insn is more than 1 byte, so how can
> GETPC() gives us the address of the CALL insn above?
>
> I guess I must misunderstood something here ....
IIRC, the result of GETPC is used for a range check. So you just have to
ensure that it points somewhere into the translated code sequence of the
current target instruction.
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux