Re: [PATCH v13 05/10] arm64: Kprobes with single stepping support

[David Long]

On 06/13/2016 02:50 AM, Masami Hiramatsu wrote:
> On Mon, 13 Jun 2016 00:10:29 -0400
> David Long <dave.long@xxxxxxxxxx> wrote:
>
> > > > ---
> > > >    arch/arm64/Kconfig                      |   1 +
> > > >    arch/arm64/include/asm/debug-monitors.h |   5 +
> > > >    arch/arm64/include/asm/insn.h           |   4 +-
> > > >    arch/arm64/include/asm/kprobes.h        |  60 ++++
> > > >    arch/arm64/include/asm/probes.h         |  44 +++
> > > >    arch/arm64/kernel/Makefile              |   1 +
> > > >    arch/arm64/kernel/debug-monitors.c      |  18 +-
> > > >    arch/arm64/kernel/kprobes-arm64.c       | 144 +++++++++
> > > >    arch/arm64/kernel/kprobes-arm64.h       |  35 +++
> > > >    arch/arm64/kernel/kprobes.c             | 526 ++++++++++++++++++++++++++++++++
> > >
> > > Not sure why kprobes.c and kprobes-arm64.c are splitted.
> >
> > This comes from the model of the arm32 kprobes code where handling of
> > the low-level instruction simulation is implemented in separate files
> > for 32-bit vs. thumb instructions.  It should make a little more sense
> > in the future when additional instruction simulation code will hopefully
> > be added for those instructions we cannot currently single-step
> > out-of-line.  It also probably *could* be merged into one file.
>
> Hmm, at least the name of arch/arm64/kernel/kprobes-arm64.c is
> meaningless. As we've done in x86, I think we can make it
> arch/arm64/kernel/kprobes/decode-insn.{c,h}

I've changed the name to kprobe-decode-insn.[hc], or do you feel 
strongly the three kprobes source files in arch/arm64/kernel need their 
own subdirectory?

> [..]
> > > > +
> > > > +/* Return:
> > > > + *   INSN_REJECTED     If instruction is one not allowed to kprobe,
> > > > + *   INSN_GOOD         If instruction is supported and uses instruction slot,
> > > > + *   INSN_GOOD_NO_SLOT If instruction is supported but doesn't use its slot.
> > >
> > > Is there any chance to return INSN_GOOD_NO_SLOT?
> >
> > Ah, that gets used later when simulation support is added.  I've removed
> > this enum value from this commit and will add it to the later one.
> > Please no one complain about using an enum instead of a bool, it will
> > eventually have three possible values.
>
> OK :)
>
> [..]
> > > > +enum kprobe_insn __kprobes
> > > > +arm_kprobe_decode_insn(kprobe_opcode_t *addr, struct arch_specific_insn *asi)
> > > > +{
> > > > +	enum kprobe_insn decoded;
> > > > +	kprobe_opcode_t insn = le32_to_cpu(*addr);
> > > > +	kprobe_opcode_t *scan_start = addr - 1;
> > > > +	kprobe_opcode_t *scan_end = addr - MAX_ATOMIC_CONTEXT_SIZE;
> > > > +#if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
> > > > +	struct module *mod;
> > > > +#endif
> > > > +
> > > > +	if (addr >= (kprobe_opcode_t *)_text &&
> > > > +	    scan_end < (kprobe_opcode_t *)_text)
> > > > +		scan_end = (kprobe_opcode_t *)_text;
> > > > +#if defined(CONFIG_MODULES) && defined(MODULES_VADDR)
> > > > +	else {
> > > > +		preempt_disable();
> > > > +		mod = __module_address((unsigned long)addr);
> > > > +		if (mod && within_module_init((unsigned long)addr, mod) &&
> > > > +			!within_module_init((unsigned long)scan_end, mod))
> > > > +			scan_end = (kprobe_opcode_t *)mod->init_layout.base;
> > > > +		else if (mod && within_module_core((unsigned long)addr, mod) &&
> > > > +			!within_module_core((unsigned long)scan_end, mod))
> > > > +			scan_end = (kprobe_opcode_t *)mod->core_layout.base;
> > >
> > > What happen if mod == NULL? it should be return error, isn't it?
> >
> > No, it should be fine.  It just means it didn't have to do either of the
> > extra checks to limit the end of the search through the code to the
> > boundary of one of the corresponding module text sections. It means the
> > instruction is in the regular kernel (non-module) text segment.
>
> Ah, I see. It is OK then. :)
>
> Thank you,

Thanks,
-dl