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    SubjectRe: [PATCH v4 03/16] x86/alternatives,jump_label: Provide better text_poke() batching interface
    On Mon, Oct 21, 2019 at 10:48:02AM +0200, Ingo Molnar wrote:
    >
    > * Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > > --- a/arch/x86/kernel/jump_label.c
    > > +++ b/arch/x86/kernel/jump_label.c
    > > @@ -35,18 +35,19 @@ static void bug_at(unsigned char *ip, in
    > > BUG();
    > > }
    > >
    > > -static void __jump_label_set_jump_code(struct jump_entry *entry,
    > > - enum jump_label_type type,
    > > - union jump_code_union *code,
    > > - int init)
    > > +static const void *
    > > +__jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init)
    > > {
    > > + static union jump_code_union code; /* relies on text_mutex */
    > > const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
    > > const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
    > > const void *expect;
    > > int line;
    > >
    > > - code->jump = 0xe9;
    > > - code->offset = jump_entry_target(entry) -
    > > + lockdep_assert_held(&text_mutex);
    > > +
    > > + code.jump = JMP32_INSN_OPCODE;
    > > + code.offset = jump_entry_target(entry) -
    > > (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
    > >
    > > if (init) {
    > > @@ -54,23 +55,23 @@ static void __jump_label_set_jump_code(s
    > > } else if (type == JUMP_LABEL_JMP) {
    > > expect = ideal_nop; line = __LINE__;
    > > } else {
    > > - expect = code->code; line = __LINE__;
    > > + expect = code.code; line = __LINE__;
    >
    > Side note: the whole 'line' logic looked weird to me and it obsfuscates
    > the logic a bit, and I had to look it up to see what it's about:
    > improving the debug output of text-patching crashes.
    >
    > How about something like the below on top of your queue? We have %phD
    > that can nicely print instructions in hex.

    I have a patch like that somewhere; see here:

    https://lkml.kernel.org/r/20191007090012.00469193.6@infradead.org

    But yes, the __LINE__ thing is mostly about identifying which case it is
    and I suppose we can infer that when we have the expected text printed
    too.

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