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Subject: Re: [PATCH v4 09/16] powerpc: Use a function for reading instructions
From: Balamuruhan S <bala24@linux.ibm.com>
To: Nicholas Piggin <npiggin@gmail.com>, Jordan Niethe <jniethe5@gmail.com>,
 linuxppc-dev@lists.ozlabs.org
Date: Mon, 23 Mar 2020 14:13:29 +0530
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On Mon, 2020-03-23 at 18:00 +1000, Nicholas Piggin wrote:
> Jordan Niethe's on March 20, 2020 3:18 pm:
> > Prefixed instructions will mean there are instructions of different
> > length. As a result dereferencing a pointer to an instruction will not
> > necessarily give the desired result. Introduce a function for reading
> > instructions from memory into the instruction data type.
> > 
> > Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> > ---
> > v4: New to series
> > ---
> >  arch/powerpc/include/asm/uprobes.h |  4 ++--
> >  arch/powerpc/kernel/kprobes.c      |  8 ++++----
> >  arch/powerpc/kernel/mce_power.c    |  2 +-
> >  arch/powerpc/kernel/optprobes.c    |  6 +++---
> >  arch/powerpc/kernel/trace/ftrace.c | 33 +++++++++++++++++++-----------
> >  arch/powerpc/kernel/uprobes.c      |  2 +-
> >  arch/powerpc/lib/code-patching.c   | 22 ++++++++++----------
> >  arch/powerpc/lib/feature-fixups.c  |  6 +++---
> >  arch/powerpc/xmon/xmon.c           |  6 +++---
> >  9 files changed, 49 insertions(+), 40 deletions(-)
> > 
> > diff --git a/arch/powerpc/include/asm/uprobes.h
> > b/arch/powerpc/include/asm/uprobes.h
> > index 2bbdf27d09b5..fff3c5fc90b5 100644
> > --- a/arch/powerpc/include/asm/uprobes.h
> > +++ b/arch/powerpc/include/asm/uprobes.h
> > @@ -23,8 +23,8 @@ typedef ppc_opcode_t uprobe_opcode_t;
> >  
> >  struct arch_uprobe {
> >  	union {
> > -		u32	insn;
> > -		u32	ixol;
> > +		u8	insn[MAX_UINSN_BYTES];
> > +		u8	ixol[MAX_UINSN_BYTES];
> >  	};
> >  };
> 
> Hmm. I wonder if this should be a different patch. Not sure if raw
> bytes is a good idea here. ppc probes also has a ppc_opcode_t, maybe
> could be replaced with ppc_insn_t and used here instead?
> 
> Also can't find where you define ppc_inst_read.

Nick, ppc_inst_read and macro PPC_INST you have asked in patch 4 are defined in
asm/inst.h with patch 3 (powerpc: Use a datatype for instructions)

-- Bala
> 
> > diff --git a/arch/powerpc/kernel/trace/ftrace.c
> > b/arch/powerpc/kernel/trace/ftrace.c
> > index 7614a9f537fd..ad451205f268 100644
> > --- a/arch/powerpc/kernel/trace/ftrace.c
> > +++ b/arch/powerpc/kernel/trace/ftrace.c
> > @@ -41,6 +41,12 @@
> >  #define	NUM_FTRACE_TRAMPS	8
> >  static unsigned long ftrace_tramps[NUM_FTRACE_TRAMPS];
> >  
> > +static long
> > +read_inst(ppc_inst *inst, const void *src)
> > +{
> > +	return probe_kernel_read((void *)inst, src, MCOUNT_INSN_SIZE);
> > +}
> 
> Humbly suggest probe_kernel_inst_read.
> 
> Thanks,
> Nick
>