[PATCH v2] ARM: stacktrace: Add USER_STACKTRACE support

[Russell King (Oracle)]

On Tue, Jul 30, 2024 at 10:15:32AM +0800, Jinjie Ruan wrote:
> Currently, userstacktrace is unsupported for ARM. So use the
> perf_callchain_user() code as blueprint to implement the
> arch_stack_walk_user() which add userstacktrace support on ARM.
> Meanwhile, we can use arch_stack_walk_user() to simplify the implementation
> of perf_callchain_user().
> 
> A ftrace test case is shown as below:
> 	# cd /sys/kernel/debug/tracing
> 	# echo 1 > options/userstacktrace
> 	# echo 1 > options/sym-userobj
> 	# echo 1 > events/sched/sched_process_fork/enable
> 	# cat trace
> 
> 	......
> 	              sh-100     [000] .....    51.779261: sched_process_fork: comm=sh pid=100 child_comm=sh child_pid=108
> 	              sh-100     [000] .....    51.779285: <user stack trace>
> 	 => /lib/libc.so.6[+0xb3c8c]
> 	 => /bin/busybox[+0xffb901f1]
> 
> Also a simple perf test is ok as below:
> 	# perf record -e cpu-clock --call-graph fp top
> 	# perf report --call-graph
> 
> 	.....
> 	  [[31m  65.00%[[m     0.00%  top      [kernel.kallsyms]  [k] __ret_fast_syscall
> 
> 	            |
> 	            ---__ret_fast_syscall
> 	               |
> 	               |--[[31m30.00%[[m--__se_sys_getdents64
> 	               |          iterate_dir
> 	               |          |
> 	               |          |--[[31m25.00%[[m--proc_pid_readdir
> 
> Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>

Do you have a use case for this feature?

Given that userspace is free to do whatever it likes with stack frames,
I think this is going to be hit and miss whether it works.

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