Role of svc_entry macro with 64 bytes in kprobes/systemtap on ARM

Role of svc_entry macro with 64 bytes in kprobes/systemtap on ARM

[Jey Jay]

Hi,

Currently Im working on "systemtap" and "kprobes".

My current work is to convert the kprobes in to loadable kernel
module(.ko) on arm architecture.

Converted module is able to run the examples in
"http://lxr.free-electrons.com/source/samples/kprobes/?a=arm".

But few systemtap scripts like

1. https://sourceware.org/systemtap/SystemTap_Beginners_Guide/traceiosect.html
2. https://sourceware.org/systemtap/SystemTap_Beginners_Guide/mainsect-disk.html#disktop

producing kernel panics.

We don't want to recompile kernel. so CONFIG_KPROBES is not set.

Because CONFIG_KPROBES, In the following file

http://lxr.free-electrons.com/source/arch/arm/kernel/entry-armv.S?a=arm

#ifdef CONFIG_KPROBES
@ If a kprobe is about to simulate a "stmdb sp..." instruction,
@ it obviously needs free stack space which then will belong to
@ the saved context.
    svc_entry 64
#else
        svc_entry
#endif


svc_entry macro is not expanded with 64. I am not sure with
relationship between svc_entry macro and kprobes.

Im getting problem exactly in
http://lxr.free-electrons.com/source/arch/arm/kernel/kprobes-common.c?a=arm#L246

Please share your knowledge.

Thanks and Regards
Jeyaram

Re: Role of svc_entry macro with 64 bytes in kprobes/systemtap on ARM

[Josh Stone]

On 12/11/2013 07:10 PM, Jey Jay wrote:
> Hi,
> 
> Currently Im working on "systemtap" and "kprobes".
> 
> My current work is to convert the kprobes in to loadable kernel
> module(.ko) on arm architecture.
> 
> Converted module is able to run the examples in
> "http://lxr.free-electrons.com/source/samples/kprobes/?a=arm".
> 
> But few systemtap scripts like
> 
> 1. https://sourceware.org/systemtap/SystemTap_Beginners_Guide/traceiosect.html
> 2. https://sourceware.org/systemtap/SystemTap_Beginners_Guide/mainsect-disk.html#disktop
> 
> producing kernel panics.

In case you aren't aware, stap has the runtime option -DSTP_ALIBI to
exculpate itself from such panics.  It basically compiles out the probe
handlers, leaving just an atomic counter to track probe hits.

Sharing the details of your kernel panics would also help.

But I'm sorry, I don't know about svc_entry myself...

Josh