Steven Rostedt <rostedt@xxxxxxxxxxx> writes: > On Sat, 17 Mar 2018 00:46:32 +1100 > Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: > >> There is a small but non-zero amount of code required by arches to >> suppory non-dynamic (static) ftrace, and more importantly there is the >> added work of testing both configurations. >> >> There are also almost no down sides to dynamic ftrace once it's well >> tested, other than a small increase in code/data size. >> >> So give arches the option to opt-out of supporting static ftrace. >> >> This is implemented as a DYNAMIC_FTRACE_CHOICE option, which controls >> whether DYNAMIC_FTRACE is presented as a user-selectable option or if >> it is just enabled based on its dependencies being enabled (because >> it's already default y). >> >> Then the CHOICE option depends on an arch *not* selecting >> HAVE_DYNAMIC_FTRACE_ONLY. This would be more natural in reverse, as a >> HAVE_STATIC_FTRACE option, but that would require updating every arch. >> >> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > > Why not just add in arch/powerpc/Kconfig: > > config PPC > [..] > select DYNAMIC_FTRACE if FUNCTION_TRACER > > ? > > It seems to work for me. It does work, but it's a bit fragile. It requires duplicating the dependencies of DYNAMIC_FTRACE in the 'if' condition. Currently that's: config DYNAMIC_FTRACE depends on FUNCTION_TRACER depends on HAVE_DYNAMIC_FTRACE So technically we should use: select DYNAMIC_FTRACE if FUNCTION_TRACER and HAVE_DYNAMIC_FTRACE Though we happen to know we just selected HAVE_DYNAMIC_FTRACE so we can leave that out. As long as the dependencies of DYNAMIC_FTRACE don't change, or the 'if' clause is updated when they do, then it's OK and it is certainly simpler. cheers
