[Qemu-devel] GDB debugging of QEMU.

[Qemu-devel] GDB debugging of QEMU.

[Yaodong Yang]

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Hello everyone,

I have a simple question about the debugging of qemu.

I used the qemu-1.5.1, and added several .c and .h files related the block
drivers. I want to debug my own implementations using gdb. but I have no
idea how to do it.

I tried the following commands.

./configure --enable-debug --disable-werror --enable-kvm
--prefix=/usr/local/kvm

make -j4

sudo make install

gdb sudo /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda
ubuntu.img -m 1024.

Could someone give me some guidance on how to use gdb in QEMU. I know the
basic usage of gdb for simple .c file, but I really donot know how to use
it in QEMU.

Thanks a lot in advance!

Yaodong

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Re: [Qemu-devel] GDB debugging of QEMU.

[Peter Maydell]

On 9 August 2013 17:45, Yaodong Yang <yaodong.yangy@gmail.com> wrote:
> I tried the following commands.
>
> ./configure --enable-debug --disable-werror --enable-kvm
> --prefix=/usr/local/kvm

--disable-werror is usually not a good idea for developers.

> make -j4
>
> sudo make install
>
> gdb sudo /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda
> ubuntu.img -m 1024.

Why are you running qemu as root here? (ie why 'sudo'?)

> Could someone give me some guidance on how to use gdb in QEMU.
> I know the basic usage of gdb for simple .c file, but I really
> do not know how to use it in QEMU.

There is no particular difference. QEMU is a bigger program
but has no particular gotchas for being debugged.

-- PMM

Re: [Qemu-devel] GDB debugging of QEMU.

[Yaodong Yang]

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Hello Peter,


Best,
Yaodong
----------------------------------------------
Yaodong Yang
Ph.D. Student
Department of Computer Science & Engineering
University of Nebraska-Lincoln 
Email: yaodong.yangy@gmail.com OR yyang@cse.unl.edu




On Aug 9, 2013, at 11:56 AM, Peter Maydell <peter.maydell@linaro.org> wrote:

> On 9 August 2013 17:45, Yaodong Yang <yaodong.yangy@gmail.com> wrote:
>> I tried the following commands.
>> 
>> ./configure --enable-debug --disable-werror --enable-kvm
>> --prefix=/usr/local/kvm
> 
> --disable-werror is usually not a good idea for developers.
I see, I will get rid of it in my development.
> 
>> make -j4
>> 
>> sudo make install
>> 
>> gdb sudo /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda
>> ubuntu.img -m 1024.
> 
> Why are you running qemu as root here? (ie why 'sudo'?)
In my implementation, I need to read and write to other raw disks, so I think I need the root permission to run this program. 
> 
>> Could someone give me some guidance on how to use gdb in QEMU.
>> I know the basic usage of gdb for simple .c file, but I really
>> do not know how to use it in QEMU.
> 
> There is no particular difference. QEMU is a bigger program
> but has no particular gotchas for being debugged.

I think I did not make my question clear. I do not know 1. how to add "-g" flag when compile QEMU, in order to use gdb 2. how to invoke QEMU with gdb, because my previous attempt failed. "gdb sudo /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda"

by the way, when I add storagemanager.c and storagemanager.h to the root directory, in order to compile and link them, I add storagemanger.o in Makefile.objs, as "block-obj-y += nbd.o  block.o  storagemanager.o" in line 10. 

Thanks a lot!
> 
> -- PMM


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Re: [Qemu-devel] GDB debugging of QEMU.

[Peter Maydell]

On 9 August 2013 18:11, Yaodong Yang <yaodong.yangy@gmail.com> wrote:
> I think I did not make my question clear. I do not know
> 1. how to add "-g" flag when compile QEMU, in order to use gdb

This is what passing --enable-debug to configure does.

> 2. how to invoke QEMU with gdb,
> because my previous attempt failed. "gdb sudo
> /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda"

This won't work because you're running gdb as your own
user and attempting to debug a program running as root.
'sudo gdb qemu-system-x86_64 ...' will probably work.

(Also, you almost certainly want to run gdb on the binary
that you just built rather than on the binary in
/usr/local/kvm/bin which is presumably whatever older
version was last installed.)

-- PMM

Re: [Qemu-devel] GDB debugging of QEMU.

[Max Filippov]

On Fri, Aug 9, 2013 at 9:14 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
> On 9 August 2013 18:11, Yaodong Yang <yaodong.yangy@gmail.com> wrote:
>> 2. how to invoke QEMU with gdb,
>> because my previous attempt failed. "gdb sudo
>> /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda"
>
> This won't work because you're running gdb as your own
> user and attempting to debug a program running as root.
> 'sudo gdb qemu-system-x86_64 ...' will probably work.
>
> (Also, you almost certainly want to run gdb on the binary
> that you just built rather than on the binary in
> /usr/local/kvm/bin which is presumably whatever older
> version was last installed.)

You also need --args when you pass arguments to the application
being debugged, so the command line looks like

sudo gdb --args /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda

-- 
Thanks.
-- Max

Re: [Qemu-devel] GDB debugging of QEMU.

[Yaodong Yang]

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It works! Thank you very much!

Best,
Yaodong
----------------------------------------------
Yaodong Yang
Ph.D. Student
Department of Computer Science & Engineering
University of Nebraska-Lincoln 
Email: yaodong.yangy@gmail.com OR yyang@cse.unl.edu




On Aug 9, 2013, at 12:25 PM, Max Filippov <jcmvbkbc@gmail.com> wrote:

> On Fri, Aug 9, 2013 at 9:14 PM, Peter Maydell <peter.maydell@linaro.org> wrote:
>> On 9 August 2013 18:11, Yaodong Yang <yaodong.yangy@gmail.com> wrote:
>>> 2. how to invoke QEMU with gdb,
>>> because my previous attempt failed. "gdb sudo
>>> /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda"
>> 
>> This won't work because you're running gdb as your own
>> user and attempting to debug a program running as root.
>> 'sudo gdb qemu-system-x86_64 ...' will probably work.
>> 
>> (Also, you almost certainly want to run gdb on the binary
>> that you just built rather than on the binary in
>> /usr/local/kvm/bin which is presumably whatever older
>> version was last installed.)
> 
> You also need --args when you pass arguments to the application
> being debugged, so the command line looks like
> 
> sudo gdb --args /usr/local/kvm/bin/qemu-system/x86_64 -s -enable-kvm -hda
> 
> -- 
> Thanks.
> -- Max


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