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Re: [Qemu-devel] Re: [PATCH 4/4] gdbstub: x86: Switch 64/32 bit register

From: Jan Kiszka
Subject: Re: [Qemu-devel] Re: [PATCH 4/4] gdbstub: x86: Switch 64/32 bit registers dynamically
Date: Mon, 29 Jun 2009 17:36:15 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

Daniel Jacobowitz wrote:
> On Mon, Jun 29, 2009 at 04:53:45PM +0200, Jan Kiszka wrote:
>> Just to recall the situation (again, please actually try it): if you
>> have to debug code that switches between 16/32 bit and 64 bit, you
>> _can't_ debug the 16 or 32 bit part as gdb will stumble and fall over
>> qemu sending 64-bit register layout for 16/32 bit code. That is a gdb
>> limitation, but this patch is about dealing with it until it's resolved
>> in gdb.
> Remind me why you can't just tell GDB that the target is 64-bit
> despite whatever file you've given it?

Because gdb mixes up arch capability and current operation mode on x86.
It always tries to disassemble according to the set arch. Moreover, it
will misinterpret the registers as being valid across all 64 bits, not
just 16 or 32. I haven't looked into further side effects, but I bet
there are more.


Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux

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