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Re: how to continue from a breakpoint in GNU/Hurd

From: Yue Lu
Subject: Re: how to continue from a breakpoint in GNU/Hurd
Date: Wed, 17 Jul 2013 01:04:55 +0800


thanks for you reply.

On Wed, Jul 17, 2013 at 12:44 AM, Luis Machado
<lgustavo@codesourcery.com> wrote:
> Hi,
> On 07/16/2013 01:28 PM, Yue Lu wrote:
>> Hi.
>> I am writing a debugger demo under GNU/Hurd when I study the gdb source
>> code. And I have met a big problem that when I set a breakpoint in the
>> inferior, my code can't resume inferior from it.
>> I can get the exception message from the mach kernel when the inferior
>> hit the breakpoint. As soon as I got the exception message, I removed
>> the int3, and set the EIP to the previous values, then post a signal
>> zero to the inferior by msg_sig_post_untraced_request(). at last I
>> called thread_resume() to resume it. But thing goes wrong, the inferior
>> is always stops at the breakpoint. and seems never to continue.
> Some general thoughts...
> Can you make sure the breakpoint has been lifted from the instruction it
> replaced? If the breakpoint has been lifted and it is still being hit, then
> it sounds like there is some kind of instruction cache problem going on,
> where we first need to flush the icache before resuming execution.
> If the icache is the problem, then it sounds like something the kernel
> itself needs to address.
> Luis

I don't know how to flush the icache off-hand, so I used anther way to
bypass this issue. I set the eip to the next instruction's address to
bypass the breakpoint ins. But problem seems doesn't go away.

Yue Lu (陆岳)

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