On Wed, 2016-01-27 at 23:28 +1030, Alan Modra wrote: > 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. OK, thanks for clarfiying. Pascal is not a big concern :D. But although I don't think we use nested functions anywhere, someone somewhere could be, or at least might one day. > r12 might be a better choice for a temp reg. Even better. cheers -- 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
