Re: arm64 uprobes support showing signs of life

[Pratyush Anand <panand at redhat dot com>]

Hi Will,


On Monday 05 January 2015 09:36 PM, William Cohen wrote:
> Hi All,
>
> Pratyush has been implementing uprobes support for aarch64 and has
> posted a set of patches
> (http://comments.gmane.org/gmane.linux.ports.arm.kernel/382237) for
> review.  The really new Linux kernels requires a patch to the
> systemtap runtime because the f_dentry macro has been removed.  With
> the patched systemtap I was able to run the systemtap testsuite and
> get some test results exercising the uprobes support:
>
> https://web.elastic.org/~dejazilla/viewsummary.php?summary=%3D%27%3C54A9E21C.2080504%40redhat.com%3E%27
>
> There looked to be a localized fixes for plt support to eliminate the
> unsupported systemtap.base/list.exp plt-* tests.
>
> A number of the tests appear to fail because of userspace arguments
> cannot be found for sdt probes.
>
> The uprobe patches still need some refinement.  On a number of
> systemtap "make installcheck" runs the kernel would get stuck spewing
> out:
>
>    Unexpected kernel single-step exception at EL1

There are at least two functions of arm64/uprobe implementation 
uprobe_breakpoint_handler and uprobe_single_step_handler, where a kprobe 
insertion might be causing above issue. Currently I have qualified these 
functions with __kprobe, so that one can not insert a kprobe there. With 
this you should not be able to see the above message.

However, I am still investigating if a kprobe insertion be allowed to 
these functions or any other function which is called directly from 
debug exception handler (do_debug_exception)

Update code is here:

https://github.com/pratyushanand/linux.git : ml_arm64_uprobe_devel_v2

~Pratyush

> However, things are looking better for user-space probing on arm64.
>
> -Will