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    Subject[RFC patch 00/32] TRACE_EVENT: cleanup for code-size reduction

    I implemented the TRACE_EVENT macros as arrays of fields and arrays of
    events in LTTng, and realised that it could benefit Ftrace too by
    cutting down its code size. As I know that code size footprint is an
    issue Steven has been wanting to tackle for a while, I am sending this
    "semicolon removal" patchset, which is a prerequisite to be able to
    generate arrays of events.

    The main difference between the approaches Ftrace and LTTng have taken
    is that Ftrace creates a "ftrace_define_fields_##call" function for each
    event which calls trace_define_field for each field of each event. In
    LTTng, I did the following (code snippet from [1]):

    struct lttng_event_field {
    const char *name;
    const struct lttng_type type;

    struct lttng_event_desc {
    const struct lttng_event_field *fields;
    const char *name;
    unsigned int nr_fields;

    #undef DEFINE_EVENT
    #define DEFINE_EVENT(_template, _name, _proto, _args) \
    { \
    .fields = __event_fields___##_template, \
    .name = #_name, \
    .nr_fields = ARRAY_SIZE(__event_fields___##_template), \

    #define TP_ID1(_token, _system) _token##_system
    #define TP_ID(_token, _system) TP_ID1(_token, _system)

    static const struct lttng_event_desc TP_ID(__event_desc___, TRACE_SYSTEM)[] = {

    And for creation of __event_fields___##_template, which allows to keep
    all fields in another array (which should be defined in a phase prior to
    the event array definition), I did:

    #undef __field
    #define __field(_type, _item) \
    { .name = #_item, .type = { .atype = atype_integer, .name = #_type} },

    (similar for __field_ext, __array, __dynamic_array, __string)

    #undef TP_STRUCT__entry
    #define TP_STRUCT__entry(args...) args /* Only one used in this phase */

    #define DECLARE_EVENT_CLASS(_name, _proto, _args, _tstruct, _assign, _print) \
    static const struct lttng_event_field __event_fields___##_name[] = { \
    _tstruct \

    For the declaration of struct lttng_type, which contains the field type
    information in a union, see [2].

    Best regards,


    Mathieu Desnoyers
    Operating System Efficiency R&D Consultant
    EfficiOS Inc.

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      Last update: 2011-05-03 00:07    [W:0.031 / U:11.432 seconds]
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