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.mari...@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. 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. -- Catalin
