Messages in this thread | | | Date | Mon, 26 Sep 2016 18:33:59 +0530 | From | Pratyush Anand <> | Subject | Re: [PATCH 5/5] arm64: Add uprobe support |
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On 26/09/2016:12:01:59 PM, Catalin Marinas wrote: > On Sun, Sep 25, 2016 at 10:32:28PM +0530, Pratyush Anand wrote: > > On Fri, Sep 23, 2016 at 6:35 PM, Catalin Marinas > > <catalin.marinas@arm.com> 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(). > > This looks like a better approach. > > > > 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(). > > Even if the is_trap_insn() check passes, we would reject the probe in > arch_uprobe_analyze_insn() immediately after based on the mm type check, > so not too bad.
OK..I will have an always returning false from arm64 is_trap_insn() in v2.
> > If we add support for probing 32-bit tasks, I would rather have > is_trap_insn() take the mm_struct as argument so that a non-weak > implementation can check for the correct encoding.
Yes, for 32 bit task we would need mm_struct as arg in is_trap_insn() as well as in is_swbp_insn(). We would also need to have arm64 specific set_swbp().
Thanks for all your input. It was helpful. I will send V2 soon.
~Pratyush
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