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    Subject[RFC PATCH 0/6] jump label v3
    hi,

    Refresh of the jump labeling patches. We introduce the following:

    # ifdef CONFIG_X86_64
    # define JUMP_LABEL_NOP P6_NOP5
    # else
    # define JUMP_LABEL_NOP ".byte 0xe9 \n\t .long 0\n\t"
    # endif

    # define JUMP_LABEL(tag, label, cond) \
    do { \
    static const char __jlstrtab_##tag[] \
    __used __attribute__((section("__jump_strings"))) = #tag; \
    asm goto("1:" \
    JUMP_LABEL_NOP \
    ".pushsection __jump_table, \"a\" \n\t" \
    _ASM_PTR "1b, %l[" #label "], %c0 \n\t" \
    ".popsection \n\t" \
    : : "i" (__jlstrtab_##tag) : : label); \
    } while (0)

    -------------

    I'm using an atomic 5 byte no-op for x86_64 and a long jump for 32-bit x86.
    My understanding is that not all 32-bit processors have an atomic 5 byte no-op,
    and thus using a long jump or jump 0, for the off case is the safest.

    which can then be used by the tracepoint code as:

    #define DECLARE_TRACE(name, proto, args) \
    extern struct tracepoint __tracepoint_##name; \
    static inline void trace_##name(proto) \
    { \
    JUMP_LABEL(name, do_trace, __tracepoint_##name.state); \
    return; \
    do_trace: \
    __DO_TRACE(&__tracepoint_##name, \
    TP_PROTO(proto), TP_ARGS(args)); \


    --------------

    Thus, in the disabled tracing case we have a no-op followed by a jump around
    the disabled code. When we enable the tracepoint, we simply patch the no-op
    with a jump to the 'do_trace' label. This relies on the 'asm goto' construct
    which is already merged into gcc 4.5. In subsequent gcc versions, we also hope
    to make use of 'cold' label for the 'do_trace' section. Thus, making the
    disabled or straight line codepath, simply a no-op.

    As discussed in pervious mails I've seen an average improvement of 30 cycles
    per-tracepoint on x86_64 systems that I've tested.

    The first 2 patches of the series are a repost of Masami's text_poke_fixup()
    function, which allows for efficient instruction patching. The final 4 patches,
    implement the the jump patching mechanism for x86 and x86_64.

    The implementation is a 'low' level one, in the sense that it is geared
    specifically for tracepoints. However, I believe this mechanism will be more
    generally useful for other parts of the kernel. Thus, I will propose 'higher'
    level interfaces into the jump label code (layered on these 'low' level ones),
    as we go.

    thanks,

    -Jason

    Masami Hiramatsu (2):
    x86: Introduce generic jump patching without stop_machine
    kprobes/x86: Cleanup RELATIVEJUMP_INSTRUCTION to RELATIVEJUMP_OPCODE

    Jason Baron(4):
    move opcode defs from asm/kprobes.h to asm/alternative.h
    jump-label-basic
    jump-module-support
    jump-label-tracepoints

    arch/x86/include/asm/alternative.h | 17 +++++
    arch/x86/include/asm/jump_label.h | 35 +++++++++++
    arch/x86/include/asm/kprobes.h | 3 -
    arch/x86/kernel/Makefile | 2 +-
    arch/x86/kernel/alternative.c | 120 ++++++++++++++++++++++++++++++++++++
    arch/x86/kernel/jump_label.c | 66 ++++++++++++++++++++
    arch/x86/kernel/kprobes.c | 2 +-
    include/asm-generic/vmlinux.lds.h | 11 +++-
    include/linux/jump_label.h | 47 ++++++++++++++
    include/linux/module.h | 12 +++-
    include/linux/tracepoint.h | 35 ++++++-----
    kernel/kprobes.c | 2 +-
    kernel/module.c | 27 ++++++++-
    kernel/tracepoint.c | 25 ++++++--
    14 files changed, 372 insertions(+), 32 deletions(-)
    create mode 100644 arch/x86/include/asm/jump_label.h
    create mode 100644 arch/x86/kernel/jump_label.c
    create mode 100644 include/linux/jump_label.h



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