[PATCH] powerpc: Allow relative pointers in bug table entries

[Jordan Niethe]

On Mon, Nov 30, 2020 at 12:42 PM Michael Ellerman <mpe at ellerman.id.au> wrote:
>
> Christophe Leroy <christophe.leroy at csgroup.eu> writes:
> > Le 27/11/2020 à 04:02, Jordan Niethe a écrit :
> >> This enables GENERIC_BUG_RELATIVE_POINTERS on Power so that 32-bit
> >> offsets are stored in the bug entries rather than 64-bit pointers.
> >>
> >> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> >> ---
> >>   arch/powerpc/Kconfig           |  4 ++++
> >>   arch/powerpc/include/asm/bug.h | 37 ++++++++++++++++++++++++++++++++--
> >>   arch/powerpc/xmon/xmon.c       | 17 ++++++++++++++--
> >>   3 files changed, 54 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> >> index e9f13fe08492..294108e0e5c6 100644
> >> --- a/arch/powerpc/Kconfig
> >> +++ b/arch/powerpc/Kconfig
> >> @@ -311,6 +311,10 @@ config GENERIC_BUG
> >>      default y
> >>      depends on BUG
> >>
> >> +config GENERIC_BUG_RELATIVE_POINTERS
> >> +    def_bool y
> >> +    depends on GENERIC_BUG
> >> +
> >>   config SYS_SUPPORTS_APM_EMULATION
> >>      default y if PMAC_APM_EMU
> >>      bool
> >> diff --git a/arch/powerpc/include/asm/bug.h b/arch/powerpc/include/asm/bug.h
> >> index 338f36cd9934..d03d834042a1 100644
> >> --- a/arch/powerpc/include/asm/bug.h
> >> +++ b/arch/powerpc/include/asm/bug.h
> >> @@ -12,7 +12,11 @@
> >>   #ifdef CONFIG_DEBUG_BUGVERBOSE
> >>   .macro EMIT_BUG_ENTRY addr,file,line,flags
> >>       .section __bug_table,"aw"
> >> +#ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> >
> > As far as I understand, as soon as CONFIG_BUG is selected, GENERIC_BUG is automatically selected so
> > GENERIC_BUG_RELATIVE_POINTERS is selected as well. Therefore this #ifndef is never possible.
>
> Yeah.
>
> There is one place in the generic code that has an ifndef CONFIG_GENERIC_BUG_RELATIVE_POINTERS
> but that's because it has to support arches that don't select it.
>
> In the arch code we know that it's enabled, so there should be no need
> for any ifdefs.
For 32bit, pointers are 4 bytes anyway so it would be pointless to
store a displacement, so won't we need some ifdefs for that?
>
> cheers