On Thu, Jun 25, 2020 at 03:40:42PM -0700, Sami Tolvanen wrote: > > Not boot tested, but it generates the required sections and they look > > more or less as expected, ymmv. > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > > index a291823f3f26..189575c12434 100644 > > --- a/arch/x86/Kconfig > > +++ b/arch/x86/Kconfig > > @@ -174,7 +174,6 @@ config X86 > > select HAVE_EXIT_THREAD > > select HAVE_FAST_GUP > > select HAVE_FENTRY if X86_64 || DYNAMIC_FTRACE > > - select HAVE_FTRACE_MCOUNT_RECORD > > select HAVE_FUNCTION_GRAPH_TRACER > > select HAVE_FUNCTION_TRACER > > select HAVE_GCC_PLUGINS > > This breaks DYNAMIC_FTRACE according to kernel/trace/ftrace.c: > > #ifndef CONFIG_FTRACE_MCOUNT_RECORD > # error Dynamic ftrace depends on MCOUNT_RECORD > #endif > > And the build errors after that seem to confirm this. It looks like we might > need another flag to skip recordmcount. Hurm, Steve, how you want to do that? > Anyway, since objtool is run before recordmcount, I just left this unchanged > for testing and ignored the recordmcount warnings about __mcount_loc already > existing. Something is a bit off still though, I see this at boot: > > ------------[ ftrace bug ]------------ > ftrace failed to modify > [<ffffffff81000660>] __tracepoint_iter_initcall_level+0x0/0x40 > actual: 0f:1f:44:00:00 > Initializing ftrace call sites > ftrace record flags: 0 > (0) > expected tramp: ffffffff81056500 > ------------[ cut here ]------------ > > Otherwise, this looks pretty good. Ha! it is trying to convert the "CALL __fentry__" into a NOP and not finding the CALL -- because objtool already made it a NOP... Weird, I thought recordmcount would also write NOPs, it certainly has code for that. I suppose we can use CC_USING_NOP_MCOUNT to avoid those, but I'd rather Steve explain this before I wreck things further.
