On Wed, 7 Mar 2018 22:16:19 +0530 "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> We can't take a trap in most parts of real mode code. Instead of adding > the 'notrace' annotation to all C functions that can be invoked from > real mode, detect that we are in real mode on ftrace entry and return > back. > > Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com> > --- > This RFC only handles -mprofile-kernel to demonstrate the approach being > considered. We will need to handle other ftrace entry if we decide to > continue down this path. I do prefer this trade off. > diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S > b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S > index 3f3e81852422..ecc0e8e38ead 100644 > --- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S > +++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S > @@ -56,6 +56,21 @@ _GLOBAL(ftrace_caller) > > /* Load special regs for save below */ > mfmsr r8 > + > + /* Only proceed if we are not in real mode and can take interrupts */ > + andi. r9, r8, MSR_IR|MSR_DR|MSR_RI > + cmpdi r9, MSR_IR|MSR_DR|MSR_RI > + beq 1f OK, I assume this check and branch is negligible compared to the mfmsr call? -- Steve > + mflr r8 > + mtctr r8 > + REST_GPR(9, r1) > + REST_GPR(8, r1) > + addi r1, r1, SWITCH_FRAME_SIZE > + ld r0, LRSAVE(r1) > + mtlr r0 > + bctr > + > +1: > mfctr r9 > mfxer r10 > mfcr r11
