x86/fgraph,bpf: Fix ORC stack unwind from return probe #6226
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This reverts commit 83f44ae. When perf_callchain_kernel calls unwind_start with first_frame, AFAICS we do not skip regs->ip, but it's added as part of the unwind process. Hence reverting the extra perf_callchain_store for non-hw regs leg. Acked-by: Song Liu <[email protected]> Signed-off-by: Jiri Olsa <[email protected]>
Currently we don't get stack trace via ORC unwinder on top of fgraph exit
handler. We can see that when generating stacktrace from kretprobe_multi
bpf program which is based on fprobe/fgraph.
The reason is that the ORC unwind code won't get pass the return_to_handler
callback installed by fgraph return probe machinery.
Solving this by creating stack frame in return_to_handler expected by
ftrace_graph_ret_addr function to recover original return address and
continue with the unwind.
Also updating the pt_regs data with cs/flags/rsp which are needed for
successful stack retrieval from ebpf bpf_get_stackid helper.
- in get_perf_callchain we check user_mode(regs) so CS has to be set
- in perf_callchain_kernel we call perf_hw_regs(regs), so EFLAGS/FIXED
has to be unset
Note I feel like it'd be better to set those directly in return_to_handler,
but Steven suggested setting them later in kprobe_multi code path.
Signed-off-by: Jiri Olsa <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Adding test that attaches kprobe/kretprobe multi and verifies the ORC stacktrace matches expected functions. It skips the test for if kernels built with frame pointer unwinder. Signed-off-by: Jiri Olsa <[email protected]>
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At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=1016271 expired. Closing PR. |
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Pull request for series with
subject: x86/fgraph,bpf: Fix ORC stack unwind from return probe
version: 1
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1016271