Re: [PATCH 5/5] arm64: Add uprobe support

[Pratyush Anand]

On Fri, Sep 23, 2016 at 6:35 PM, Catalin Marinas
<catalin.marinas@xxxxxxx> wrote:
> On Fri, Sep 23, 2016 at 09:42:30AM +0530, Pratyush Anand wrote:
>> On 22/09/2016:05:50:30 PM, Catalin Marinas wrote:
>> > On Thu, Sep 22, 2016 at 08:53:28AM +0530, Pratyush Anand wrote:
>> > > On 21/09/2016:06:04:04 PM, Catalin Marinas wrote:

>> > As a quick workaround you could check mm->task_size > TASK_SIZE_32 in
>> > the arch_uprobe_analyze_insn() function.
>>
>> It would be doable. TASK_SIZE_32 is defined only for COMPAT. So, may be I can
>> return -EINVAL when mm->task_size < TASK_SIZE_64.
>
> That's just a temporary workaround. If we ever merge ILP32, this test
> would no longer be enough (as the ISA is AArch64 but with TASK_SIZE_32).

OK.. So what about doing something similar what x86 is doing.
We can have a flag for task Type in arch specific mm_context_t. We
also set this flag in COMPAT_SET_PERSONALITY() along with setting
thread_info flag, and we clear them in SET_PERSONALITY().

>
> Looking at prepare_uprobe(), we have a weak is_trap_insn() function.
> This check is meaningless without knowing which instruction set we
> target. A false positive here, however, is not that bad as we wouldn't
> end up inserting the wrong breakpoint in the executable. But it looks to
> me like the core uprobe code needs to pass some additional information
> like the type of task or ELF format to the arch code to make a useful
> choice of breakpoint type.

It seems that 'strtle r0, [r0], #160' would have the closest matching
aarch32 instruction wrt BRK64_OPCODE_UPROBES(0xd42000A0). But that too
seems a bad instruction. So, may be we can use still weak
is_trap_insn().

~Pratyush