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In-Reply-To: <20200113113015.GA5532@dhcp-9-109-246-161.in.ibm.com>
From: Jordan Niethe <jniethe5@gmail.com>
Date: Fri, 7 Feb 2020 10:09:58 +1100
Message-ID: <CACzsE9pm84v_QfRo8aw5JRZ5r8zwFRUKXj6Hug=-TA99UwhZvA@mail.gmail.com>
Subject: Re: [PATCH 15/18] powerpc/uprobes: Add support for prefixed
 instructions
To: Balamuruhan S <bala24@linux.ibm.com>
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Cc: Alistair Popple <alistair@popple.id.au>, linuxppc-dev@lists.ozlabs.org
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On Mon, Jan 13, 2020 at 10:30 PM Balamuruhan S <bala24@linux.ibm.com> wrote:
>
> On Tue, Nov 26, 2019 at 04:21:38PM +1100, Jordan Niethe wrote:
> > Uprobes can execute instructions out of line. Increase the size of the
> > buffer used  for this so that this works for prefixed instructions. Take
> > into account the length of prefixed instructions when fixing up the nip.
> >
> > Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> > ---
> >  arch/powerpc/include/asm/uprobes.h | 18 ++++++++++++++----
> >  arch/powerpc/kernel/uprobes.c      |  4 ++--
> >  2 files changed, 16 insertions(+), 6 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/uprobes.h b/arch/powerpc/include/asm/uprobes.h
> > index 2bbdf27d09b5..5b5e8a3d2f55 100644
> > --- a/arch/powerpc/include/asm/uprobes.h
> > +++ b/arch/powerpc/include/asm/uprobes.h
> > @@ -14,18 +14,28 @@
> >
> >  typedef ppc_opcode_t uprobe_opcode_t;
> >
> > +/*
> > + * We have to ensure we have enought space for prefixed instructions, which
>
> minor typo of `enought` and we can have something like below,
Thanks for catching that.
>
> s/We have to ensure we have enought/Ensure we have enough
Will do.
>
> -- Bala
>
> > + * are double the size of a word instruction, i.e. 8 bytes. However,
> > + * sometimes it is simpler to treat a prefixed instruction like 2 word
> > + * instructions.
> > + */
> >  #define MAX_UINSN_BYTES              4
> > -#define UPROBE_XOL_SLOT_BYTES        (MAX_UINSN_BYTES)
> > +#define UPROBE_XOL_SLOT_BYTES        (2 * MAX_UINSN_BYTES)
> >
> >  /* The following alias is needed for reference from arch-agnostic code */
> >  #define UPROBE_SWBP_INSN     BREAKPOINT_INSTRUCTION
> >  #define UPROBE_SWBP_INSN_SIZE        4 /* swbp insn size in bytes */
> >
> >  struct arch_uprobe {
> > +      /*
> > +       * Ensure there is enough space for prefixed instructions. Prefixed
> > +       * instructions must not cross 64-byte boundaries.
> > +       */
> >       union {
> > -             u32     insn;
> > -             u32     ixol;
> > -     };
> > +             uprobe_opcode_t insn[2];
> > +             uprobe_opcode_t ixol[2];
> > +     } __aligned(64);
> >  };
> >
> >  struct arch_uprobe_task {
> > diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
> > index ab1077dc6148..cfcea6946f8b 100644
> > --- a/arch/powerpc/kernel/uprobes.c
> > +++ b/arch/powerpc/kernel/uprobes.c
> > @@ -111,7 +111,7 @@ int arch_uprobe_post_xol(struct arch_uprobe *auprobe, struct pt_regs *regs)
> >        * support doesn't exist and have to fix-up the next instruction
> >        * to be executed.
> >        */
> > -     regs->nip = utask->vaddr + MAX_UINSN_BYTES;
> > +     regs->nip = utask->vaddr + ((IS_PREFIX(auprobe->insn[0])) ? 8 : 4);
> >
> >       user_disable_single_step(current);
> >       return 0;
> > @@ -173,7 +173,7 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
> >        * emulate_step() returns 1 if the insn was successfully emulated.
> >        * For all other cases, we need to single-step in hardware.
> >        */
> > -     ret = emulate_step(regs, auprobe->insn, 0);
> > +     ret = emulate_step(regs, auprobe->insn[0], auprobe->insn[1]);
> >       if (ret > 0)
> >               return true;
> >
> > --
> > 2.20.1
> >
>