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

[Nicholas Piggin]

Jordan Niethe's on March 23, 2020 8:09 pm:
> 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.

Okay.

> 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;
> }

Ah, yeah I did mean that, you probably told me that already.

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

I didn't mean that, but it would be nicer than the change you've got,
if it works.

>> 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.

It's probably not too bad, you could add a __ or ppc_ prefix if
it would help?

Thanks,
Nick