From: Renlin Li <renlin.li@arm.com>
To: Shiva Chen <shiva0217@gmail.com>
Cc: "gcc@gcc.gnu.org" <gcc@gcc.gnu.org>
Subject: Re: Aarch64 implementation for dwarf exception handling
Date: Thu, 13 Feb 2014 14:32:00 -0000 [thread overview]
Message-ID: <52FCD786.1040407@arm.com> (raw)
In-Reply-To: <CAH=PD7byDjYwq3KjpR=THt-HO6a73Zy9abq8_Zttg8kqjy-VMw@mail.gmail.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
next prev parent reply other threads:[~2014-02-13 14:32 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-13 2:15 Shiva Chen
2014-02-13 11:41 ` Yufeng Zhang 张玉峰
2014-02-13 14:32 ` Renlin Li [this message]
2014-02-13 15:37 ` Shiva Chen
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