[uml-devel] Programs in guest segfault, amd64 host and guest

[uml-devel] Programs in guest segfault, amd64 host and guest

[Jan Dittmer]

- Guest 2.6.19-rc1-git11
- Host Debian 2.6.18-1-amd64
- Debian etch for host and guest
- both using ext3
- command to start the guest
./linux-2.6.19-rc1-git11 ubd0=umlblob.cow,etch-amd64.img \
    eth0=daemon,10:00:00:00:00:02,unix,/var/run/uml-utilities/uml_switch.ctl \
         mem=128M \
         con=null umid=umlprey \
         >/dev/null 2>&1 &


$ strace btlaunchmany /tmp/
...
mmap(NULL, 8392704, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|0x40, 
-1, 0) = 0x41c4e000
mprotect(0x41c4e000, 4096, PROT_NONE)   = 0
clone(Process 484 attached
child_stack=0x4244e280, 
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID|CLONE_DETACHED, 
parent_tidptr=0x4244e9f0, tls=0x4244e960, child_tidptr=0x4244e9f0) = 484
[pid   483] rt_sigprocmask(SIG_SETMASK, [],  <unfinished ...>
[pid   484] --- SIGSEGV (Segmentation fault) @ 0 (0) ---
Process 484 detached
<... rt_sigprocmask resumed> NULL, 8)   = 0
+++ killed by SIGSEGV +++
Process 483 detached

$ strace mlnet -stdout
...
gettimeofday({1161185543, 817872}, NULL) = 0
mmap(NULL, 8392704, PROT_READ|PROT_WRITE|PROT_EXEC, 
MAP_PRIVATE|MAP_ANONYMOUS|0x40, -1, 0) = 0x41ccd000
mprotect(0x41ccd000, 4096, PROT_NONE)   = 0
clone(child_stack=0x424cd270, 
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID|CLONE_DETACHED, 
parent_tidptr=0x424cd9f0, tls=0x424cd960, child_tidptr=0x424cd9f0) = 502
gettimeofday({1161185543, 820912}, NULL) = 0
poll([{fd=7, events=POLLIN}, {fd=6, events=POLLIN}, {fd=5, events=POLLIN}, 
{fd=4, events=POLLIN}, {fd=3, events=POLLIN}], 5, 96) = -1 EINTR 
(Interrupted system call)
+++ killed by SIGSEGV +++
Process 501 detached

Additionally I'm having build failure compiling ARCH=um SUBARCH=i386.

Thanks for any pointers,

Jan


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Re: [uml-devel] Programs in guest segfault, amd64 host and guest

[Jeff Dike]

On Wed, Oct 18, 2006 at 05:33:50PM +0200, Jan Dittmer wrote:
> clone(Process 484 attached
> child_stack=0x4244e280, 
> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID|CLONE_DETACHED, 
> parent_tidptr=0x4244e9f0, tls=0x4244e960, child_tidptr=0x4244e9f0) = 484
> [pid   483] rt_sigprocmask(SIG_SETMASK, [],  <unfinished ...>
> [pid   484] --- SIGSEGV (Segmentation fault) @ 0 (0) ---
> Process 484 detached
> <... rt_sigprocmask resumed> NULL, 8)   = 0
> +++ killed by SIGSEGV +++

I suspect it's due to UML/x86_64 having incomplete NPTL support,
although I've had almost no problems with up-to-date Fedora
filesystems on x86_64.  The one thing I do see is yum segfaulting
occassionally, but I haven't been able to tie that to NPTL.

				Jeff

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Re: [uml-devel] Programs in guest segfault, amd64 host and guest

[Jan Dittmer]

Jeff Dike wrote:
> On Wed, Oct 18, 2006 at 05:33:50PM +0200, Jan Dittmer wrote:
>> clone(Process 484 attached
>> child_stack=0x4244e280, 
>> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID|CLONE_DETACHED, 
>> parent_tidptr=0x4244e9f0, tls=0x4244e960, child_tidptr=0x4244e9f0) = 484
>> [pid   483] rt_sigprocmask(SIG_SETMASK, [],  <unfinished ...>
>> [pid   484] --- SIGSEGV (Segmentation fault) @ 0 (0) ---
>> Process 484 detached
>> <... rt_sigprocmask resumed> NULL, 8)   = 0
>> +++ killed by SIGSEGV +++
> 
> I suspect it's due to UML/x86_64 having incomplete NPTL support,
> although I've had almost no problems with up-to-date Fedora
> filesystems on x86_64.  The one thing I do see is yum segfaulting
> occassionally, but I haven't been able to tie that to NPTL.

This is 100% reproducible here. Perfect test case. How to debug?

Jan

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Re: [uml-devel] Programs in guest segfault, amd64 host and guest

[Nikola Ciprich]

try exporting LD_ASSUME_KERNEL=2.4.1 before executing Your application, 
to see if that works - this disables usage of NPTL
Jan Dittmer wrote:
> Jeff Dike wrote:
>   
>> On Wed, Oct 18, 2006 at 05:33:50PM +0200, Jan Dittmer wrote:
>>     
>>> clone(Process 484 attached
>>> child_stack=0x4244e280, 
>>> flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID|CLONE_DETACHED, 
>>> parent_tidptr=0x4244e9f0, tls=0x4244e960, child_tidptr=0x4244e9f0) = 484
>>> [pid   483] rt_sigprocmask(SIG_SETMASK, [],  <unfinished ...>
>>> [pid   484] --- SIGSEGV (Segmentation fault) @ 0 (0) ---
>>> Process 484 detached
>>> <... rt_sigprocmask resumed> NULL, 8)   = 0
>>> +++ killed by SIGSEGV +++
>>>       
>> I suspect it's due to UML/x86_64 having incomplete NPTL support,
>> although I've had almost no problems with up-to-date Fedora
>> filesystems on x86_64.  The one thing I do see is yum segfaulting
>> occassionally, but I haven't been able to tie that to NPTL.
>>     
>
> This is 100% reproducible here. Perfect test case. How to debug?
>
> Jan
>
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>   


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Re: [uml-devel] Programs in guest segfault, amd64 host and guest

[Jeff Dike]

On Wed, Oct 18, 2006 at 09:16:14PM +0200, Jan Dittmer wrote:
> This is 100% reproducible here. Perfect test case. How to debug?

You want to dig into the code and see what's wrong?  Put a breakpoint
on the force_sig_info(SIGSEGV, ...) in segv().  Then find the faulting
instruction -
	RIP is regs.skas.regs[16]
	pid = cpu_tasks[0].pid
	Look in the host's /proc/$pid/maps for the page containing RIP
	add uml_physmem to the offset in column 3 - that's the
physical page containing RIP
	add the RIP page offset to that to get the actual physical
address for RIP
	disassemble the range of memory around it - I usually do 10 -
20 bytes before it to ~10 bytes after
	see that the asm looks sane, if not, bump the start of the
disassembly by a byte in either direction until it does
	see what the instruction at RIP is - if it involves a gs:
reference, then it's very likely a NPTL problem

If you don't want to do that, tell me what to yum, and how to run
whatever it is, and I'll look at it.

				Jeff

	

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Re: [uml-devel] Programs in guest segfault, amd64 host and guest

[Jan Dittmer]

Jeff Dike wrote:
> On Wed, Oct 18, 2006 at 09:16:14PM +0200, Jan Dittmer wrote:
>> This is 100% reproducible here. Perfect test case. How to debug?
> 
> You want to dig into the code and see what's wrong?  Put a breakpoint
> on the force_sig_info(SIGSEGV, ...) in segv().  Then find the faulting
> instruction -
> 	RIP is regs.skas.regs[16]
> 	pid = cpu_tasks[0].pid
> 	Look in the host's /proc/$pid/maps for the page containing RIP
> 	add uml_physmem to the offset in column 3 - that's the
> physical page containing RIP
> 	add the RIP page offset to that to get the actual physical
> address for RIP
> 	disassemble the range of memory around it - I usually do 10 -
> 20 bytes before it to ~10 bytes after
> 	see that the asm looks sane, if not, bump the start of the
> disassembly by a byte in either direction until it does
> 	see what the instruction at RIP is - if it involves a gs:
> reference, then it's very likely a NPTL problem

Well tomorrow perhaps. I've very little time currently :-(

> If you don't want to do that, tell me what to yum, and how to run
> whatever it is, and I'll look at it.

As I wrote in the original message: Debian/etch amd64 host+guest,
running btlaunchmany (from the bittorrent package). I can put you
the compressed root + kernel somewhere if that helps. It's roughly
100mb.

Jan

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Re: [uml-devel] Programs in guest segfault, amd64 host and guest

[Jeff Dike]

On Wed, Oct 18, 2006 at 11:25:18PM +0200, Jan Dittmer wrote:
> As I wrote in the original message: Debian/etch amd64 host+guest,
> running btlaunchmany (from the bittorrent package). I can put you
> the compressed root + kernel somewhere if that helps. It's roughly
> 100mb.

Yeah, that would be useful.

				Jeff

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