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    SubjectRe: [PATCH 4/5] x86: entry_64.S: always allocate complete "struct pt_regs"
    On Mon, Aug 11, 2014 at 5:40 PM, Jan Beulich <JBeulich@suse.com> wrote:
    >>>> 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.
    >

    How does one test the entry CFI annotations? The best that I know of
    is to single-step through using gdb attached to qemu and see whether
    backtraces seem to work.

    --Andy


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