Re: [Patch] New gdbarch method "dwarf_cfa_op" and migrate SPARC to it

[Ivo Raisr <ivo.raisr@oracle.com>]

On 19.4.2017 12:17, Jiong Wang wrote:
> Hi,
>
> Recently a feature called "return address signing" has been added to GCC to
> prevent stack smash stack on AArch64.  For details please refer:
>
>   https://gcc.gnu.org/ml/gcc-patches/2017-01/msg00376.html
>
> GDB needs to be aware of this feature so it can restore the original return
> address which is critical for unwinding.
>
> On compiler side, whenever return address, i.e. LR register, is mangled or
> restored by hardware instruction, compiler is expected to generate a
> DW_CFA_GNU_window_save CFA instruction to toggle the LR signing status.
> DW_CFA_GNU_window_save was introduced by SPARC for their register window
> feature, here AArch64 want to multiplex this DWARF CFA instruction as
> it's in vendor space.  So, a new gdbarch method, dwarf_cfa_op, is introduced.

Are you sure to reuse DW_CFA_GNU_window_save for AArch64 purposes? 
Because semantics of DW_CFA_GNU_window_save (implied from "window save") 
mean much more than just fiddling with return address. For example as 
you learned from dwarf2-frame.c, whole register window needs to be copied.


>   SPARC-linux cross gdb build OK.

I have built gdb on sparc64-linux with your changes and no new 
regressions are introduced in the test suite. So the patch is ok w.r.t. 
this.

I.