Re: Aarch64 implementation for dwarf exception handling

[Shiva Chen <shiva0217@gmail.com>]

Hi, Yufeng

Sorry, I don't have any testcase
I just mis-understanding the implementation.


Hi, Renlin

Thanks to point out my mis-understanding.
I didn't aware that LP would in different position between FP needed
(bottom of callee) and FP not needed(top of callee).
I have check the aarch64_layout_frame() and find out the FP/LP will
push as last register by aarch64_save_or_restore_callee_save_registers
() if FP is not needed.

Thanks for your kindly help,
I really appreciate it.

Shiva


2014-02-13 22:32 GMT+08:00 Renlin Li <renlin.li@arm.com>:
> On 13/02/14 02:14, Shiva Chen wrote:
>>
>> Hi,
>>
>> I have a question about the implementation of
>>
>> aarch64_final_eh_return_addr
>>
>> which is used to point out the return address of the frame
>>
>> According the source code
>>
>> If FP is not needed
>>
>>    return gen_frame_mem (DImode,
>>                          plus_constant (Pmode,
>>                                         stack_pointer_rtx,
>>                                         fp_offset
>>                                         +
>> cfun->machine->frame.saved_regs_size
>>                                         - 2 * UNITS_PER_WORD));
>>
>>
>> According the frame layout
>>
>>          +-------------------------------+ <-- arg_pointer_rtx
>>          |
>>          |  callee-allocated save area
>>          |  for register varargs
>>          |
>>          +-------------------------------+
>>          |
>>          |  local variables
>>          |
>>          +-------------------------------+ <-- frame_pointer_rtx
>>          |
>>          |  callee-saved registers
>>          |
>>          +-------------------------------+
>>          |  LR'
>>          +-------------------------------+
>>          |  FP'
>>         P+-------------------------------+ <-- hard_frame_pointer_rtx
>>          |  dynamic allocation
>>          +-------------------------------+
>>          |
>>          |  outgoing stack arguments
>>          |
>>          +-------------------------------+ <-- stack_pointer_rtx
>>
>> Shouldn't the return value be
>>
>>    return gen_frame_mem (DImode,
>>                          plus_constant (Pmode,
>>                                         stack_pointer_rtx,
>>                                         fp_offset
>>                                         +  2* UNITS_PER_WORD));
>>
>> Or I just mis-understanding something ?
>>
>>
>> Hope someone could give me a tip.
>>
>> It would be very helpful.
>>
>> Thanks
>>
>> Shiva Chen
>>
> Hi,
>
> If frame pointer is not needed. The prologue routine will store the callee
> saved registers to stack according to ascending order, which means X0 will
> be saved first if needed, and X30(LR) will be the last if it's pushed into
> stack.
>
> Please check the source code, aarch64_layout_frame().
>
> As the comment above the code also indicates, LR would be at the top of the
> saved registers block().
>
> By the way, there is one additional stack slot might be needed to keep stack
> pointer 16-byte aligned,  so - 2 * UNITS_PER_WORD is needed to adjust the
> load  address.
>
>         +-------------------------------+ <-- arg_pointer_rtx
>         |
>         +-------------------------------+ <-- frame_pointer_rtx
>         |  dummy
>         |  LR
>         |  bla...bla...
>         |  x3
>         |  x2
>         |  x1
>         |  x0
>       P +-------------------------------+ <-- hard_frame_pointer_rtx
>         |
>         +-------------------------------+ <-- stack_pointer_rtx
>
>
> Kind regards,
> Renlin
>