On Wed, Jan 27, 2016 at 09:19:27PM +1100, Michael Ellerman wrote: > Hi Torsten, > > On Mon, 2016-01-25 at 16:26 +0100, Torsten Duwe wrote: > > The gcc switch -mprofile-kernel, available for ppc64 on gcc > 4.8.5, > > allows to call _mcount very early in the function, which low-level > > ASM code and code patching functions need to consider. > > Especially the link register and the parameter registers are still > > alive and not yet saved into a new stack frame. > > > > Signed-off-by: Torsten Duwe <duwe@xxxxxxx> > > --- > > arch/powerpc/kernel/entry_64.S | 45 +++++++++++++++++++++++++++++++++++++++-- > > arch/powerpc/kernel/ftrace.c | 12 +++++++++-- > > arch/powerpc/kernel/module_64.c | 14 +++++++++++++ > > 3 files changed, 67 insertions(+), 4 deletions(-) > > > > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S > > index a94f155..e7cd043 100644 > > --- a/arch/powerpc/kernel/entry_64.S > > +++ b/arch/powerpc/kernel/entry_64.S > > @@ -1206,7 +1206,12 @@ _GLOBAL(enter_prom) > > #ifdef CONFIG_DYNAMIC_FTRACE > > _GLOBAL(mcount) > > _GLOBAL(_mcount) > > - blr > > + std r0,LRSAVE(r1) /* gcc6 does this _after_ this call _only_ */ > > + mflr r0 > > + mtctr r0 > > + ld r0,LRSAVE(r1) > > + mtlr r0 > > + bctr > > Can we use r11 instead? eg: > > _GLOBAL(_mcount) > mflr r11 > mtctr r11 > mtlr r0 > bctr Depends on what you need to support. As Torsten says, the code to call _mcount when -mprofile-kernel is emitted before the prologue of a function (similar to -m32), but after the ELFv2 global entry point code. If you trash r11 here you're killing the static chain pointer, used by C nested functions or other languages that use a static chain, eg. Pascal. r11 has *not* been saved for ELFv2. r12 might be a better choice for a temp reg. -- Alan Modra Australia Development Lab, IBM -- To unsubscribe from this list: send the line "unsubscribe live-patching" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
