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SubjectRe: [PATCH 4/5] x86: entry_64.S: always allocate complete "struct pt_regs"
>>> On 11.08.14 at 02:46, <fweisbec@gmail.com> wrote:
> On Mon, Aug 04, 2014 at 05:03:42AM +0200, Denys Vlasenko wrote:
>> On Sat, Aug 2, 2014 at 1:19 AM, Frederic Weisbecker <fweisbec@gmail.com>
> wrote:
>> >> CFI_ESCAPE 0x0f /* DW_CFA_def_cfa_expression */, 6, \
>> >> 0x77 /* DW_OP_breg7 */, 0, \
>> >> 0x06 /* DW_OP_deref */, \
>> >> - 0x08 /* DW_OP_const1u */, SS+8-RBP, \
>> >> + 0x08 /* DW_OP_const1u */, SS+8, \
>> >> 0x22 /* DW_OP_plus */
>> >> /* We entered an interrupt context - irqs are off: */
>> >> TRACE_IRQS_OFF
>> >> -
>> >> call \func
>> >> .endm
>> >>
>> >> @@ -749,10 +719,9 @@ ret_from_intr:
>> >>
>> >> /* Restore saved previous stack */
>> >> popq %rsi
>> >
>> > And then you pop to rsi. Ok that indeed works but perhaps we should keep it symetrical
>> > just for clarity? Any reason why we can't reuse rdi here?
>>
>> I changed this entire area in v2: basically, I will not change the logic,
>> but will add comments explaining what are we doing here, and why.
>> (Some minor code changes will be done, not affecting the logic).
>>
>> While we are at it, what this CFI_ESCAPE thing does here?
>> As usual, it has no comment :/

Each of its lines has a comment; with other CFI annotations not
each having comments, I don't see what else is needed here.

> I don't know, only Jan Beulich understands those CFI black magic.

That would be very said if true.

In any case: This needs to be a CFI_ESCAPE because there's no
other way I know of to emit the DW_CFA_def_cfa_expression.
And the change to it looks correct to me.

Jan



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