[Qemu-devel] Re: Question on implementatio of GETPC()

[Jan Kiszka <jan.kiszka@siemens.com>]

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

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