[PATCH v4 09/16] powerpc: Use a function for reading instructions

[Jordan Niethe]

On Mon, Mar 23, 2020 at 7:03 PM Nicholas Piggin <npiggin at gmail.com> 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 at 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?
You are right this should not really be in this patch. I felt bytes
made sense as we have  MAX_UINSN_BYTES, which could be updated once
prefixed instructions were introduced.
By replace do you mean define uprobe_opcode_t as ppc_inst_t instead of
ppc_opcode_t? That will not really work with the arch indep code in
places like:

bool __weak is_swbp_insn(uprobe_opcode_t *insn)
{
    return *insn == UPROBE_SWBP_INSN;
}

Or do you mean something like this:
  struct arch_uprobe {
       union {
 -             u32     insn;
 -             u32     ixol;
 +             pcc_inst_t     insn;
 +             ppc_inst_t     ixol;
       };
 };

>
> Also can't find where you define ppc_inst_read.
>
> > 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.
The other probe_kernel_*  functions were from generic code so I
thought it might be misleading to call it that.
>
> Thanks,
> Nick
>