Hi Steve, On Sun, May 22, 2016 at 04:28:49PM -0400, Steven Rostedt wrote: > From: Steven Rostedt <[email protected]> > > 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 <[email protected]> > 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. > > Link: http://lkml.kernel.org/r/[email protected]
Shouldn't it go to the stable tree? Thanks, Namhyung > > Reported-by: Matt Fleming <[email protected]> > Reported-by: Namhyung Kim <[email protected]> > Tested-by: Matt Fleming <[email protected]> > Reviewed-by: Masami Hiramatsu <[email protected]> > Signed-off-by: Steven Rostedt <[email protected]> > --- > arch/x86/kernel/mcount_64.S | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S > index ed48a9f465f8..61924222a9e1 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) > > -- > 2.8.0.rc3 > >
