Re: [PATCH] ArmPkg/DefaultExceptionHandlerLib ARM: avoid endless loop in RELEASE builds

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

On Tue, 11 Dec 2018 at 15:03, Leif Lindholm <leif.lindholm@linaro.org> wrote:
>
> On Tue, Dec 11, 2018 at 02:25:10PM +0100, Ard Biesheuvel wrote:
> > Ensure that we prevent the CPU from proceeding after having taken an
> > unhandled exception on a RELEASE build, which does not contain the
> > ASSERT() which ensures this on DEBUG and NOOPT builds.
>
> Sounds like a good idea.
> Some silly questions below:
>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > ---
> >  ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c b/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
> > index 0b9da031b47d..9d96d5aabd96 100644
> > --- a/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
> > +++ b/ArmPkg/Library/DefaultExceptionHandlerLib/Arm/DefaultExceptionHandler.c
> > @@ -267,10 +267,15 @@ DefaultExceptionHandler (
> >    DEBUG ((EFI_D_ERROR, "\n"));
> >    ASSERT (FALSE);
> >
> > +  if (!PcAdjust) {
>
> Won't this always be 0 for a RELEASE build? (By convention if nothing else.)
> And won't we already have ASSERTed in any other case?
>

Yeah. I had it in my mind that you could set PcAdjust from the
debugger, but that doesn't really fly given that the optimizer will
just get rid of it in a RELEASE build, and you'd hit the ASSERT()
otherwise.



> > +    CpuDeadLoop ();
> > +  }
> > +
> >    // Clear the error registers that we have already displayed incase some one wants to keep going
> >    SystemContext.SystemContextArm->DFSR = 0;
> >    SystemContext.SystemContextArm->IFSR = 0;
> >
> >    // If some one is stepping past the exception handler adjust the PC to point to the next instruction
> >    SystemContext.SystemContextArm->PC += PcAdjust;
> > +
>
> Hmm?
>

Oops.