On Wed, Aug 3, 2016 at 9:54 AM, Pratyush Anand <pan...@redhat.com> wrote: > Hi Masami, > > On 03/08/2016:12:45:24 AM, Masami Hiramatsu wrote: >> On Tue, 2 Aug 2016 12:14:06 +0530 >> Pratyush Anand <pan...@redhat.com> wrote: >> >> > uprobe_pre_sstep_notifier and uprobe_post_sstep_notifier are called from >> > debug exception handler, so blacklist them for kprobing. >> >> Actually, these exception notifers are kicked only if the debug exception >> is not related to kprobes (at least on x86). In that case, we don't have >> to take care about that. Or, would you hit any problem on it? > > Well, I have faced issue on ARM64. So, if I have a kprobe instrumented at > these > functions and then if I hit a uprobe then kernel goes into an infinite loop of > "Unexpected kernel single-step exception at EL1". > > On x86 I have not tested, but I see that all functions except > arch_uprobe_exception_notify() in the call stack of > uprobe_pre/post_sstep_notifier() are blacklisted for kprobe. So, I am unable > to > understand that why arch_uprobe_exception_notify() and > uprobe_pre/post_sstep_notifier() are not blacklisted. > >> >> IOW, where do we have to prohibit kprobes are, the code path from where >> right after the breakpoint (debug) exception is occurred, to where right >> before the kprobe is handled. After that, it should be safe. > > Hummmm...My understanding was that if a function a() is not good to be kprobed > then we can not kprobe any function called by a() as well. Thanks for the > clarification. So, if I go with your definition then, something is still > wrong on > ARM64 which is causing issue when I kprobe uprobe_pre/post_sstep_notifier().
I found that one modification in ARM64 kprobe code allows me to kprobe uprobe_pre/post_sstep_notifier(). So, taking back this patch. Will discuss ARM64 modification on arm mailing list. Thanks Masami for your input. ~Pratyush