Unable to single-step in kvm, always results in a resume

Hi All,

I am trying to single-step through my kernel using qemu and kvm. I have run qemu via: qemu-system-x86_64 -s -S -hda /home/nickamon/lab1/obj/kernel.img and also connected to the process using gdb.

Problem is that whenever I try and step instruction, it seems to resume my kernel rather than allowing me to progress instruction by instruction. I have built the kvm snapshot from git and still no luck. Tried following the code for a few hours and have no luck. Any suggestions?

Quoted 7 lines · Nicholas Amon

Hi All,

I am trying to single-step through my kernel using qemu and kvm. I have run qemu via: qemu-system-x86_64 -s -S -hda /home/nickamon/lab1/obj/kernel.img and also connected to the process using gdb.

Quoted 5 lines

Problem is that whenever I try and step instruction, it seems to resume my kernel rather than allowing me to progress instruction by instruction. I have built the kvm snapshot from git and still no luck. Tried following the code for a few hours and have no luck. Any suggestions?

What's you host kernel or kvm-kmod version?

Hi Jan,

Thanks for responding. Yes, I am able to step instruction when I disable kvm w/ the no-kvm option. My host kernel is 64bit 2.6.27 and the program that I am debugging is 32 bit but starts in real mode. But the KVM module I am running is from kvm-88. Is there anyway I can check the version definitively?

Thanks,

Nicholas

Quoted 25 lines · Jan Kiszka

Quoted 9 lines · Jan Kiszka

Quoted 7 lines · Nicholas Amon

Hi All,

I am trying to single-step through my kernel using qemu and kvm. I have run qemu via: qemu-system-x86_64 -s -S -hda /home/nickamon/lab1/obj/kernel.img and also connected to the process using gdb.

Quoted 9 lines

Quoted 6 lines

Problem is that whenever I try and step instruction, it seems to resume my kernel rather than allowing me to progress instruction by instruction. I have built the kvm snapshot from git and still no luck. Tried following the code for a few hours and have no luck. Any suggestions?

What's you host kernel or kvm-kmod version?

...and does -no-kvm make any difference (except that it's much slower)?

Jan

Hi Nicholas,

please don't drop CCs on reply.

Quoted 4 lines · Nicholas Amon

Hi Jan,

Thanks for responding. Yes, I am able to step instruction when I disable kvm w/ the no-kvm option. My host kernel is 64bit 2.6.27 and the program that I am debugging is 32 bit but starts in real mode. But the KVM module I am running is from kvm-88. Is there anyway I can check the version definitively?

kvm modules issue a message when being loaded, check your kernel log. qemu-kvm gives you the version via -version.

OK, the problems you see is likely related to the very old versions you use. Update to recent kvm-kmod (2.6.32 series) and qemu-kvm (0.12 series) and retry.

Jan

Quoted 35 lines

Thanks,

Nicholas

Quoted 29 lines · Jan Kiszka

Quoted 10 lines · Jan Kiszka

Quoted 7 lines · Nicholas Amon

Hi All,

I am trying to single-step through my kernel using qemu and kvm. I have run qemu via: qemu-system-x86_64 -s -S -hda /home/nickamon/lab1/obj/kernel.img and also connected to the process using gdb.

Quoted 10 lines

Quoted 6 lines

Problem is that whenever I try and step instruction, it seems to resume
my kernel rather than allowing me to progress instruction by
instruction. I have built the kvm snapshot from git and still no luck. Tried following the code for a few hours and have no luck. Any suggestions?

What's you host kernel or kvm-kmod version?

...and does -no-kvm make any difference (except that it's much slower)?

Jan

Hi Nicholas,

please don't drop CCs on reply.

Quoted 4 lines · Nicholas Amon

Hi Jan,

Thanks for responding. Yes, I am able to step instruction when I disable kvm w/ the no-kvm option. My host kernel is 64bit 2.6.27 and the program that I am debugging is 32 bit but starts in real mode. But the KVM module I am running is from kvm-88. Is there anyway I can check the version definitively?

kvm modules issue a message when being loaded, check your kernel log. qemu-kvm gives you the version via -version.

OK, the problems you see is likely related to the very old versions you use. Update to recent kvm-kmod (2.6.32 series) and qemu-kvm (0.12 series) and retry.

Jan

Quoted 35 lines

Thanks,

Nicholas

Quoted 29 lines · Jan Kiszka

Quoted 10 lines · Jan Kiszka

Quoted 7 lines · Nicholas Amon

Hi All,

I am trying to single-step through my kernel using qemu and kvm. I have run qemu via: qemu-system-x86_64 -s -S -hda /home/nickamon/lab1/obj/kernel.img and also connected to the process using gdb.

Quoted 10 lines

Quoted 6 lines

Problem is that whenever I try and step instruction, it seems to resume
my kernel rather than allowing me to progress instruction by
instruction. I have built the kvm snapshot from git and still no luck. Tried following the code for a few hours and have no luck. Any suggestions?

What's you host kernel or kvm-kmod version?

...and does -no-kvm make any difference (except that it's much slower)?

Jan

So now I can step instruction but my breakpoints do not work. I have verified that disabling kvm restores the breakpoint functionality. Any suggestions?

Quoted 60 lines · Jan Kiszka

Hi Nicholas,

please don't drop CCs on reply.

Quoted 8 lines · Nicholas Amon

Hi Jan,

Thanks for responding. Yes, I am able to step instruction when I disable kvm w/ the no-kvm option. My host kernel is 64bit 2.6.27 and the program that I am debugging is 32 bit but starts in real mode. But the KVM module I am running is from kvm-88. Is there anyway I can check the version definitively?

kvm modules issue a message when being loaded, check your kernel log. qemu-kvm gives you the version via -version.

OK, the problems you see is likely related to the very old versions you use. Update to recent kvm-kmod (2.6.32 series) and qemu-kvm (0.12 series) and retry.

Jan

Quoted 36 lines

Thanks,

Nicholas

Quoted 30 lines · Jan Kiszka

Quoted 10 lines · Jan Kiszka

Quoted 7 lines · Nicholas Amon

Hi All,

I am trying to single-step through my kernel using qemu and kvm. I have run qemu via: qemu-system-x86_64 -s -S -hda /home/nickamon/lab1/obj/kernel.img and also connected to the process using gdb.

Quoted 11 lines

Quoted 7 lines

Problem is that whenever I try and step instruction, it seems to resume my kernel rather than allowing me to progress instruction by instruction. I have built the kvm snapshot from git and still no luck. Tried following the code for a few hours and have no luck. Any suggestions?

What's you host kernel or kvm-kmod version?

...and does -no-kvm make any difference (except that it's much slower)?

Jan

Quoted 2 lines · Nicholas Amon

So now I can step instruction but my breakpoints do not work. I have verified that disabling kvm restores the breakpoint functionality. Any suggestions?

What kind of breakpoints, hardware-assisted or normal BPs? Are you trying to break into real-mode code (as stated below - BTW, top-postings should be avoided!) that happens to run on a non-brand-new Intel host? I never fully tested how well guest debugging works if KVM has to emulate instructions, and I wouldn't be surprised if there are "limitations".

Jan

Quoted 66 lines

Quoted 64 lines · Jan Kiszka

Hi Nicholas,

please don't drop CCs on reply.

Quoted 5 lines · Nicholas Amon

Hi Jan,

Thanks for responding. Yes, I am able to step instruction when I disable kvm w/ the no-kvm option. My host kernel is 64bit 2.6.27 and the program that I am debugging is 32 bit but starts in real mode. But the KVM module I am running is from kvm-88. Is there anyway I can check the version definitively?

kvm modules issue a message when being loaded, check your kernel log. qemu-kvm gives you the version via -version.

OK, the problems you see is likely related to the very old versions you use. Update to recent kvm-kmod (2.6.32 series) and qemu-kvm (0.12 series) and retry.

Jan

Quoted 41 lines

Thanks,

Nicholas

Quoted 34 lines · Jan Kiszka

Quoted 11 lines · Jan Kiszka

Quoted 7 lines · Nicholas Amon

Hi All,

I am trying to single-step through my kernel using qemu and kvm. I have run qemu via: qemu-system-x86_64 -s -S -hda /home/nickamon/lab1/obj/kernel.img and also connected to the process using gdb.

Quoted 12 lines

Quoted 7 lines

Problem is that whenever I try and step instruction, it seems to resume
my kernel rather than allowing me to progress instruction by
instruction. I have built the kvm snapshot from git and still no luck. Tried following the code for a few hours and have no luck. Any suggestions?

What's you host kernel or kvm-kmod version?

...and does -no-kvm make any difference (except that it's much slower)?

Jan