Ingo, Did you want to take this patch through the tip tree, or do you want me to take it?
Thanks, -- Steve On Mon, 16 May 2016 23:00:35 -0400 Steven Rostedt <rost...@goodmis.org> wrote: > Matt Fleming reported seeing crashes when enabling and disabling > function profiling which uses function graph tracer. Later Namhyung Kim > hit a similar issue and he found that the issue was due to the jmp to > ftrace_stub in ftrace_graph_call was only two bytes, and when it was > changed to jump to the tracing code, it overwrote the ftrace_stub that > was after it. > > Masami Hiramatsu bisected this down to a binutils change: > > 8dcea93252a9ea7dff57e85220a719e2a5e8ab41 is the first bad commit > commit 8dcea93252a9ea7dff57e85220a719e2a5e8ab41 > Author: H.J. Lu <hjl.to...@gmail.com> > Date: Fri May 15 03:17:31 2015 -0700 > > Add -mshared option to x86 ELF assembler > > This patch adds -mshared option to x86 ELF assembler. By default, > assembler will optimize out non-PLT relocations against defined non-weak > global branch targets with default visibility. The -mshared option tells > the assembler to generate code which may go into a shared library > where all non-weak global branch targets with default visibility can > be preempted. The resulting code is slightly bigger. This option > only affects the handling of branch instructions. > > Declaring ftrace_stub as a weak call prevents gas from using two byte > jumps to it, which would be converted to a jump to the function graph > code. > > Reported-by: Matt Fleming <m...@codeblueprint.co.uk> > Reported-by: Namhyung Kim <namhy...@kernel.org> > Tested-by: Matt Fleming <m...@codeblueprint.co.uk> > Reviewed-by: Masami Hiramatsu <mhira...@kernel.org> > Signed-off-by: Steven Rostedt <rost...@goodmis.org> > --- > diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S > index ed48a9f465f8..e13a695c3084 100644 > --- a/arch/x86/kernel/mcount_64.S > +++ b/arch/x86/kernel/mcount_64.S > @@ -182,7 +182,8 @@ GLOBAL(ftrace_graph_call) > jmp ftrace_stub > #endif > > -GLOBAL(ftrace_stub) > +/* This is weak to keep gas from relaxing the jumps */ > +WEAK(ftrace_stub) > retq > END(ftrace_caller) > >
