[lttng-dev] LTTng system call tracing on ARM

Jan Glauber jan.glauber at gmail.com
Thu Apr 11 04:20:34 EDT 2013 

On Wed, Apr 10, 2013 at 12:39:50PM -0400, Mathieu Desnoyers wrote:
> * Jan Glauber (jan.glauber at gmail.com) wrote:
> > On Wed, Apr 10, 2013 at 12:20:12PM -0400, Mathieu Desnoyers wrote:
> > > 
> > > Thanks for the detailed report !!
> > > 
> > > Please try with this commit:
> > 
> > Yes, that patch works. But I'm still curious if you can explain what the
> > override was for ;-
> 
> The "override" allows defining how to serialize the information for
> specific system calls. It can either replace the behavior of the
> "semi-automated" description of the system call (brought into
> lttng-modules by means of the system call extractor script), or just
> provide the serialization description for a system call that was not
> available to the system call extractor.
> 
> In this case, sys_set_tls was not available for automated extraction, so
> the override entry has been added to it would not appear as a
> "sys_unknown" system call, but would rather show "sys_set_tls" along
> with the well-printed system call arguments.

OK, thanks for explaining. So the version in instrumentation/syscalls/headers
doesn't mean much, its just the starting point from where the extractor
script picked up the descriptions.

So we could append recent system calls without generating new headers for
lets say 3.4.
 
> You may want to have a look at:
> 
> lttng-modules/instrumentation/syscalls/README
> 
> for details.
> 
> If we want to handle the set_tls special-case (and same for other
> ARM-specific syscalls), we'll probably want to do that with a
> arm-specific table that will contain those system calls.

Yes, a seperate table would solve the issue. I don't know if ARM is the
only arch doing such tricks to the system call table, so it might be worth
checkingt that.

Thanks,
Jan

> Thanks,
> 
> Mathieu
> 
> 
> > 
> > --Jan
> >  
> > > commit 11fa478f18241fedee86f7dc7820a91c629c9e7e
> > > Author: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > > Date:   Wed Apr 10 12:14:38 2013 -0400
> > > 
> > >     Fix: remove ARM set_tls system call override
> > >     
> > >     We'll need to find a better way to instrument ARM-specific system calls
> > >     located at a far offset from the standard systems calls. A 16MB
> > >     lttng-modules kernel module is really not acceptable.
> > >     
> > >     Removing this instrumentation for now. sys_set_tls will appear as
> > >     sys_unknown.
> > >     
> > >     Fixes #472
> > >     
> > >     CC: Ryan Kyser <Ryan.Kyser at jci.com>
> > >     Ref: http://lists.lttng.org/pipermail/lttng-dev/2013-April/019990.html
> > >     Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> > > 
> > > diff --git a/instrumentation/syscalls/headers/arm-32-syscalls-2.6.38_integers_override.h b/instrumentation/syscalls/headers/arm-32-syscalls-2.6.38_integers_override.h
> > > index 93b8674..895370f 100644
> > > --- a/instrumentation/syscalls/headers/arm-32-syscalls-2.6.38_integers_override.h
> > > +++ b/instrumentation/syscalls/headers/arm-32-syscalls-2.6.38_integers_override.h
> > > @@ -2,7 +2,6 @@
> > >  
> > >  #define OVERRIDE_TABLE_32_sys_arm_fadvise64_64
> > >  #define OVERRIDE_TABLE_32_sys_sync_file_range2
> > > -#define OVERRIDE_TABLE_32_sys_set_tls
> > >  
> > >  #ifndef CREATE_SYSCALL_TABLE
> > >  
> > > @@ -38,18 +37,6 @@ SC_TRACE_EVENT(sys_sync_file_range2,
> > >  	TP_printk()
> > >  )
> > >  
> > > -SC_TRACE_EVENT(sys_set_tls,
> > > -	TP_PROTO(unsigned int tid, unsigned long tls),
> > > -	TP_ARGS(tid, tls),
> > > -	TP_STRUCT__entry(
> > > -		__field(unsigned int, tid)
> > > -		__field_hex(unsigned int, tls)),
> > > -	TP_fast_assign(
> > > -		tp_assign(tid, tid)
> > > -		tp_assign(tls, tls)),
> > > -	TP_printk()
> > > -)
> > > -
> > >  #else	/* CREATE_SYSCALL_TABLE */
> > >  
> > >  #define OVVERRIDE_TABLE_32_sys_mmap
> > > @@ -59,9 +46,6 @@ TRACE_SYSCALL_TABLE(sys_mmap, sys_mmap, 90, 6)
> > >  TRACE_SYSCALL_TABLE(sys_arm_fadvise64_64, sys_arm_fadvise64_64, 270, 4)
> > >  #define OVERRIDE_TABLE_32_sys_sync_file_range2
> > >  TRACE_SYSCALL_TABLE(sys_sync_file_range2, sys_sync_file_range2, 341, 4)
> > > -#define OVERRIDE_TABLE_32_sys_set_tls
> > > -TRACE_SYSCALL_TABLE(sys_set_tls, sys_set_tls, 0xf0005, 2)
> > > -
> > >  
> > >  #endif /* CREATE_SYSCALL_TABLE */
> > >  
> > > 
> > > 
> > > > 
> > > > --Jan
> > > > 
> > > > > -PL
> > > > > 
> > > > > 
> > > > > 
> > > > > On Wed, Apr 10, 2013 at 9:02 AM, Jan Glauber <jan.glauber at gmail.com> wrote:
> > > > > 
> > > > > > On Wed, Apr 10, 2013 at 08:37:18AM -0400, PLSTC wrote:
> > > > > > > Hey Jan,
> > > > > > >
> > > > > > > I cannot speak on behalf of everyone here, but during our attempt to port
> > > > > > > LTTng to Android, we also noticed that the kernels we were using (3.0.x)
> > > > > > > were nowhere near the requirements for syscall tracepoints support. I
> > > > > > > believe such support was added on x86/64 way earlier (early 3.x) than on
> > > > > > > ARM, which is why it was included in LTTng's modules a while ago. Simply
> > > > > > > put, the ARM kernel is late.
> > > > > >
> > > > > > OK, so for ARM kernel version 3.6 is the minimum unless the syscall
> > > > > > tracepoint
> > > > > > support is backported.
> > > > > >
> > > > > > > There are a few actuals ways to 'enable' syscall tracepoints support on
> > > > > > > early ARM kernels, but they all including a bit of kernel
> > > > > > hacking/patching.
> > > > > > > I could send you some links if you're interested in that.
> > > > > >
> > > > > > Yes, sure!
> > > > > >
> > > > > > --Jan
> > > > > >
> > > > > > > -PL
> > > > > > > On Apr 10, 2013 4:40 AM, "Jan Glauber" <jan.glauber at gmail.com> wrote:
> > > > > > >
> > > > > > > > Hi,
> > > > > > > >
> > > > > > > > I want to use LTTng for system call tracing on ARM. Now lttng-modules
> > > > > > seems
> > > > > > > > to support system call tracing on ARM already since
> > > > > > > > "8f4f80e LTTng Modules ARM syscall instrumentation".
> > > > > > > >
> > > > > > > > But I wonder how that worked since lttng-syscalls.c is only build under
> > > > > > > > CONFIG_HAVE_SYSCALL_TRACEPOINTS and that was added to ARM only with
> > > > > > kernel
> > > > > > > > 3.6
> > > > > > > > (much after than the lttng-modules commit).
> > > > > > > >
> > > > > > > > Am I missing something? Is system call tracing working on ARM with the
> > > > > > > > upstream
> > > > > > > > LTTng version?
> > > > > > > >
> > > > > > > > thanks,
> > > > > > > > Jan
> > > > > > > >
> > > > > > > > _______________________________________________
> > > > > > > > lttng-dev mailing list
> > > > > > > > lttng-dev at lists.lttng.org
> > > > > > > > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> > > > > > > >
> > > > > >
> > > > 
> > > > _______________________________________________
> > > > lttng-dev mailing list
> > > > lttng-dev at lists.lttng.org
> > > > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> > > 
> > > -- 
> > > Mathieu Desnoyers
> > > EfficiOS Inc.
> > > http://www.efficios.com
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

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