• Steven Rostedt (VMware)'s avatar
    ftrace/x86: Allow for arguments to be passed in to ftrace_regs by default · 02a474ca
    Steven Rostedt (VMware) authored
    Currently, the only way to get access to the registers of a function via a
    ftrace callback is to set the "FL_SAVE_REGS" bit in the ftrace_ops. But as this
    saves all regs as if a breakpoint were to trigger (for use with kprobes), it
    is expensive.
    
    The regs are already saved on the stack for the default ftrace callbacks, as
    that is required otherwise a function being traced will get the wrong
    arguments and possibly crash. And on x86, the arguments are already stored
    where they would be on a pt_regs structure to use that code for both the
    regs version of a callback, it makes sense to pass that information always
    to all functions.
    
    If an architecture does this (as x86_64 now does), it is to set
    HAVE_DYNAMIC_FTRACE_WITH_ARGS, and this will let the generic code that it
    could have access to arguments without having to set the flags.
    
    This also includes having the stack pointer being saved, which could be used
    for accessing arguments on the stack, as well as having the function graph
    tracer not require its own trampoline!
    Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
    02a474ca
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