Subject: Re: powerpc ftrace broken due to "manual merge of the ftrace tree with the arm64 tree"

From: Qian Cai <[email-masked]>
Date: Fri, 15 Nov 2019 16:06:34 -0500

On Fri, 2019-11-15 at 16:02 -0500, Steven Rostedt wrote:
> On Fri, 15 Nov 2019 15:28:52 -0500
> Qian Cai <[email-masked]> wrote:
> 
> > # echo function >/sys/kernel/debug/tracing/current_tracer
> > 
> > It hangs forever with today's linux-next on powerpc. Reverted the conflict fix
> > [1] as below fixes the issue.
> > 
> > [1] https://lore.kernel.org/linux-next/[email-masked]/
> 
> What's your config file.

https://raw.githubusercontent.com/cailca/linux-mm/master/powerpc.config

> 
> And can you test the two conflicting commits to see which one caused
> your error?
> 
> Test this commit please: b83b43ffc6e4b514ca034a0fbdee01322e2f7022

# git reset --hard b83b43ffc6e4b514ca034a0fbdee01322e2f7022

Yes, that one is bad.

> 
> And see if the issue is with that one, and not with the one without it.
> 
> -- Steve
> 
> 
> > 
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-
> > generic/vmlinux.lds.h
> > index 7d0d03a03d4d..a92222f79b53 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -136,29 +136,20 @@
> >  #endif
> >  
> >  #ifdef CONFIG_FTRACE_MCOUNT_RECORD
> > -/*
> > - * The ftrace call sites are logged to a section whose name depends on the
> > - * compiler option used. A given kernel image will only use one, AKA
> > - * FTRACE_CALLSITE_SECTION. We capture all of them here to avoid header
> > - * dependencies for FTRACE_CALLSITE_SECTION's definition.
> > - */
> > -/*
> > - * Need to also make ftrace_graph_stub point to ftrace_stub
> > - * so that the same stub location may have different protocols
> > - * and not mess up with C verifiers.
> > - */
> > -#define MCOUNT_REC()	. = ALIGN(8);				\
> > +#ifdef CC_USING_PATCHABLE_FUNCTION_ENTRY
> > +#define MCOUNT_REC()	. = ALIGN(8)				\
> >  			__start_mcount_loc = .;			\
> > -			KEEP(*(__mcount_loc))			\
> >  			KEEP(*(__patchable_function_entries))	\
> >  			__stop_mcount_loc = .;			\
> >  			ftrace_graph_stub = ftrace_stub;
> >  #else
> > -# ifdef CONFIG_FUNCTION_TRACER
> > -#  define MCOUNT_REC()	ftrace_graph_stub = ftrace_stub;
> > -# else
> > -#  define MCOUNT_REC()
> > -# endif
> > +#define MCOUNT_REC()	. = ALIGN(8);				\
> > +			__start_mcount_loc = .;			\
> > +			KEEP(*(__mcount_loc))			\
> > +			__stop_mcount_loc = .;
> > +#endif
> > +#else
> > +#define MCOUNT_REC()
> >  #endif
> >  
> >  #ifdef CONFIG_TRACE_BRANCH_PROFILING
> 
>