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

From: Luis Machado
Subject: Re: how to continue from a breakpoint in GNU/Hurd
Date: Tue, 16 Jul 2013 13:44:13 -0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130623 Thunderbird/17.0.7


On 07/16/2013 01:28 PM, Yue Lu wrote:

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.


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