On Mon, 16 May 2016 21:03:59 +0200 Borislav Petkov <[email protected]> wrote:
> On Mon, May 16, 2016 at 11:24:53PM +0900, Namhyung Kim wrote: > > > -GLOBAL(ftrace_stub) > > > +/* This is weak to keep gas from relaxing the jumps */ > > > +WEAK(ftrace_stub) > > > retq > > > END(ftrace_caller) > > You could also force the 5-byte jump. I guess you could also write > simply ".long 0" in there but this way it is more robust if someone > decides to add other stuff between the JMP and the ftrace_stub label. > > --- > diff --git a/arch/x86/kernel/mcount_64.S b/arch/x86/kernel/mcount_64.S > index ed48a9f465f8..b1db8a584c06 100644 > --- a/arch/x86/kernel/mcount_64.S > +++ b/arch/x86/kernel/mcount_64.S > @@ -179,7 +179,9 @@ GLOBAL(ftrace_epilogue) > > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > GLOBAL(ftrace_graph_call) > - jmp ftrace_stub > + .byte 0xe9 > + .long ftrace_stub - 1f > +1: > #endif > I actually thought about this first, but I thought it rather a hack (although one could argue all of function tracing is a hack ;-) But as the "weak" call was used to fix one location, why not use it here too. Being consistent, and also making sure all calls to ftrace_stub do the same. -- Steve
