Messages in this thread | | | Date | Tue, 25 Oct 2011 17:49:06 +0200 | From | Oleg Nesterov <> | Subject | Re: test-case (Was: [PATCH 12/X] uprobes: x86: introduce abort_xol()) |
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On 10/25, Srikar Dronamraju wrote: > > > > static inline void *uc_ip(struct ucontext *ctxt) > > { > > return (void*)ctxt->uc_mcontext.gregs[16]; > > } > > ... > > > I have tested this on both x86_32 and x86_64 and can confirm that the > behaviour is same with or without uprobes placed at that instruction. > This is on the uprobes code with your changes.
Great, thanks.
> However on x86_32; the output is different from x86_64. > > On x86_32 (I have additionally printed the uc_ip and fault_insn. > > SIGSEGV! ip=0x10246 addr=0x12345678 > ERR!! wrong ip uc_ip(ctxt) = 10246 fault_insn = 804856c
Yep. uc_ip() is not correct on x86_32. Sorry, I forgot to mention this.
I was really surprised when I wrote this test. I simply can't understand how can I play with ucontext in the user-space. I guess uc_ip() should use REG_EIP instead of 16, but I wasn't able to compile it even if I added __USE_GNU. It would be even better to use sigcontext instead of the ugly mcontext_t, but this looks "impossible". The kernel is much simpler ;)
> I still trying to dig up what uc_ip is and why its different on x86_32.
See above. I guess it needs ctxt->uc_mcontext.gregs[14]. Or REG_EIP.
uc_ip() simply reads sigcontext->ip passed by setup_sigcontext().
> Also I was thinking on your suggestion of making abort_xol a weak > function. In which case we could have architecture independent function > in kernel/uprobes.c which is just a wrapper for set_instruction_pointer. > > void __weak abort_xol(struct pt_regs *regs, struct uprobe_task *utask) > { > set_instruction_pointer(regs, utask->vaddr); > } > > where it would called from uprobe_notify_resume() as > > abort_xol(regs, utask); > > If other archs would want to do something else, they could override > abort_xol definition.
I didn't suggest this ;) But looks reasonable to me. And afaics x86_32 can use this arch-independent function.
Oleg.
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