• Steven Rostedt's avatar
    ftrace: use a real variable for ftrace_nop in x86 · 8115f3f0
    Steven Rostedt authored
    Impact: avoid section mismatch warning, clean up
    
    The dynamic ftrace determines which nop is safe to use at start up.
    When it finds a safe nop for patching, it sets a pointer called ftrace_nop
    to point to the code. All call sites are then patched to this nop.
    
    Later, when tracing is turned on, this ftrace_nop variable is again used
    to compare the location to make sure it is a nop before we update it to
    an mcount call. If this fails just once, a warning is printed and ftrace
    is disabled.
    
    Rakib Mullick noted that the code that sets up the nop is a .init section
    where as the nop itself is in the .text section. This is needed because
    the nop is used later on after boot up. The problem is that the test of the
    nop jumps back to the setup code and causes a "section mismatch" warning.
    
    Rakib first recommended to convert the nop to .init.text, but as stated
    above, this would fail since that text is used later.
    
    The real solution is to extend Rabik's patch, and to make the ftrace_nop
    into an array, and just save the code from the assembly to this array.
    
    Now the section can stay as an init section, and we have a nop to use
    later on.
    Reported-by: default avatarRakib Mullick <rakib.mullick@gmail.com>
    Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    8115f3f0
ftrace.c 4.12 KB