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 Post subject: Debugging an i386 userspace on an amd64 target
PostPosted: Mon Aug 12, 2019 8:13 pm 
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Joined: Mon Aug 12, 2019 7:48 pm
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I recently ported my x86 kernel to support x64 and I'm having a problem debugging applications in gdb+qemu. Before I would load the kernel into gdb, pause execution then load the userland application and execute it. Now because of architecture mixing gdb can't change the debug architecture to 32-bit and it can't backtrace or display local variables correctly.

Is there at least a better way to debug applications than this?


Last edited by ameame on Mon Aug 12, 2019 9:31 pm, edited 2 times in total.

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 Post subject: Re: Debugging an i386 userspace on an amd64 target
PostPosted: Mon Aug 12, 2019 9:25 pm 
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Are you the fellow who asked the core dump question on Stackoverflow recently?


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 Post subject: Re: Debugging an i386 userspace on an amd64 target
PostPosted: Mon Aug 12, 2019 9:27 pm 
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If you ported your OS to 64-bit then why would it be running 32-bit code? Do you switch tom 32-bit compatibility mode to execute 32-bit userland (ring 3) code?


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 Post subject: Re: Debugging an i386 userspace on an amd64 target
PostPosted: Mon Aug 12, 2019 9:29 pm 
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MichaelPetch wrote:
Are you the fellow who asked the core dump question on Stackoverflow recently?

Nah, never posted to stackoverflow before.

MichaelPetch wrote:
If you ported your OS to 64-bit then why would it be running 32-bit code? Do you switch tom 32-bit compatibility mode to execute 32-bit userland code?

Oops, that was a mistake. I mean't ported my kernel to 64-bit. My processes run in compatibility mode.


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 Post subject: Re: Debugging an i386 userspace on an amd64 target
PostPosted: Mon Aug 12, 2019 9:59 pm 
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Sounds like you are running into this issue that started becoming a problem as of 2.9 of QEMU: https://bugs.launchpad.net/qemu/+bug/1686170 . Any chance you could build 2.8.1 of QEMU and try?


Last edited by MichaelPetch on Tue Aug 13, 2019 10:06 am, edited 1 time in total.

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 Post subject: Re: Debugging an i386 userspace on an amd64 target
PostPosted: Mon Aug 12, 2019 10:51 pm 
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MichaelPetch wrote:
Sounds like you are running into this issue that started becoming an issue as of 2.9 of QEMU: https://bugs.launchpad.net/qemu/+bug/1686170 . Any chance you could build 2.8.1 of QEMU and try?

Thanks, it worked! I did have to do the disconnect trick and patch in some files so it's compatible with my glibc though.


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