[Bug target/79793] Incorrect stack alignment for interrupt handler in 64-bit

[ubizjak at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79793

--- Comment #9 from Uroš Bizjak <ubizjak at gmail dot com> ---
Created attachment 41826
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41826&action=edit
Adjust INCOMING_FRAME_SP_OFFSET for TYPE_EXCEPTION functions

How about something like attached patch? The patch adjusts
INCOMING_FRAME_SP_OFFSET of an exception handler to 2 * UNITS_PER_WORD.

The resulting code reads:

        .cfi_startproc
        subq    $392, %rsp
        .cfi_def_cfa_offset 400
        fxsave64        -120(%rsp)
        addq    $400, %rsp
        .cfi_def_cfa_offset 0
        iretq
        .cfi_endproc

Patch is otherwise untested. Probably, function argument parsing code has to be
adjusted as well. I'm also not sure if all .cfi directives are correct.