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    ftrace: Allow dynamically allocated function tracers · cdbe61bf
    Steven Rostedt 提交于
    Now that functions may be selected individually, it only makes sense
    that we should allow dynamically allocated trace structures to
    be traced. This will allow perf to allocate a ftrace_ops structure
    at runtime and use it to pick and choose which functions that
    structure will trace.
    
    Note, a dynamically allocated ftrace_ops will always be called
    indirectly instead of being called directly from the mcount in
    entry.S. This is because there's no safe way to prevent mcount
    from being preempted before calling the function, unless we
    modify every entry.S to do so (not likely). Thus, dynamically allocated
    functions will now be called by the ftrace_ops_list_func() that
    loops through the ops that are allocated if there are more than
    one op allocated at a time. This loop is protected with a
    preempt_disable.
    
    To determine if an ftrace_ops structure is allocated or not, a new
    util function was added to the kernel/extable.c called
    core_kernel_data(), which returns 1 if the address is between
    _sdata and _edata.
    
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Signed-off-by: NSteven Rostedt <rostedt@goodmis.org>
    cdbe61bf
ftrace.c 85.8 KB