arm64 kprobes/systemtap support progress

[William Cohen]

On 11/02/2014 04:02 PM, William Cohen wrote:
> Hi All,
> 
> Dave Long has been working on getting arm64 kprobes support merged into the upstream kernels.  The kprobes64 branch of the git tree at 
> https://git.linaro.org/people/dave.long/linux.git
> 

A bit more poking around with the arm64 kprobe support and found that it does not work well with smp at the moment. There appears to be some issues in linux/arch/arm64/kernel/insn.c and getting the processors to patch in the kprobe breakpoint. After booting the machine in uniprocessor mode (kernel boot parameter maxcpus=1) the kprobes were much more stable. I was able to run the systemtap syscall tests with:

make installcheck RUNTESTFLAGS="--debug systemtap.syscall/*syscall.exp"

There were a lot of failures on arm64 due to a number of the syscalls being remapped.  An incomplete list of the syscall mappings:

open -> openat
chmod -> fchmodat
chown -> fchown
lchown -> fchownat
mkdir -> mkdirat
rmdir -> unlinkat
dup2 -> dup3
inotify_init -> inotify_init1
link -> linkat
readlink -> readlinkat
symlink -> symlinkat


Thus, get the following mediocre results from the syscall tests:


		=== systemtap Summary ===

# of expected passes		110
# of unexpected failures	70
# of untested testcases		2
# of unsupported tests		4


I am getting more adventurous and trying to run more of the systemtap testsuite to see what other things are not right on arm64.

-Will