test-case (Was: [PATCH 12/X] uprobes: x86: introduce abort_xol())

[Oleg Nesterov <oleg@redhat.com>]

On 10/21, Oleg Nesterov wrote:
>
> On 10/21, Ananth N Mavinakayanahalli wrote:
> >
> > On Fri, Oct 21, 2011 at 08:12:07PM +0530, Srikar Dronamraju wrote:
> >
> > > > +void abort_xol(struct pt_regs *regs)
> > > > +{
> > > > +	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > > > +	// !!! Dear Srikar and Ananth, please implement me !!!
> > > > +	// !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > > > +	struct uprobe_task *utask = current->utask;
> > > > +	regs->ip = utask->vaddr;
> > >
> > > nit:
> > > Shouldnt we be setting the ip to the next instruction after this
> > > instruction?
> >
> > No, since we should re-execute the original instruction
>
> Yes,

In case it was not clear, I meant "agree with your 'No'".

> > after removing
> > the breakpoint.
>
> No? we should not remove this uprobe?
>
> > Also, wrt ip being set to the next instruction on a breakpoint hit,
> > that's arch specific.
>
> Probably yes, I am not sure. But:
>
> > For instance, on x86, it points to the next
> > instruction,
>
> No?
>
> 	/**
> 	 * get_uprobe_bkpt_addr - compute address of bkpt given post-bkpt regs
> 	 * @regs: Reflects the saved state of the task after it has hit a breakpoint
> 	 * instruction.
> 	 * Return the address of the breakpoint instruction.
> 	 */
> 	unsigned long __weak get_uprobe_bkpt_addr(struct pt_regs *regs)
> 	{
> 		return instruction_pointer(regs) - UPROBES_BKPT_INSN_SIZE;
> 	}
>
> Yes, initially regs->ip points to the next insn after int3, but
> utask->vaddr == get_uprobe_bkpt_addr() == addr of int3.

Ananth, Srikar, I'd suggest this test-case:

	#include <stdio.h>
	#include <signal.h>
	#include <ucontext.h>

	void *fault_insn;

	static inline void *uc_ip(struct ucontext *ctxt)
	{
		return (void*)ctxt->uc_mcontext.gregs[16];
	}

	void segv(int sig, siginfo_t *info, void *ctxt)
	{
		static int cnt;

		printf("SIGSEGV! ip=%p addr=%p\n", uc_ip(ctxt), info->si_addr);

		if (uc_ip(ctxt) != fault_insn)
			printf("ERR!! wrong ip\n");
		if (info->si_addr != (void*)0x12345678)
			printf("ERR!! wrong addr\n");

		if (++cnt == 3)
			signal(SIGSEGV, SIG_DFL);
	}

	int main(void)
	{
		struct sigaction sa = {
			.sa_sigaction	= segv,
			.sa_flags	= SA_SIGINFO,
		};

		sigaction(SIGSEGV, &sa, NULL);

		fault_insn = &&label;

	label:
		asm volatile ("movl $0x0,0x12345678");

		return 0;
	}

result:

	$ ulimit -c unlimited

	$ ./segv
	SIGSEGV! ip=0x4006eb addr=0x12345678
	SIGSEGV! ip=0x4006eb addr=0x12345678
	SIGSEGV! ip=0x4006eb addr=0x12345678
	Segmentation fault (core dumped)

	$ gdb -c ./core.1826
	...
	Program terminated with signal 11, Segmentation fault.
	#0  0x00000000004006eb in ?? ()

Now. If you insert uprobe at asm("movl") insn, result should be the same
or the patches I sent are wrong. In particular, the addr in the coredump
should be correct too. And consumer->handler() should be called 3 times
too. This insn is really executed 3 times.

I have no idea how can I test this.

Oleg.

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