x86/fgraph,bpf: Fix stack ORC unwind from kprobe_multi return probe

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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

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20251104215405.168643-3-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>

...

This commit is contained in:

Jiri Olsa 2025-11-04 22:54:03 +01:00 • committed by Alexei Starovoitov

parent 6d08340d1e

commit 20a0bc1027

3 changed files with 21 additions and 2 deletions

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5

arch/x86/include/asm/ftrace.h

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8

arch/x86/kernel/ftrace_64.S

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10

include/linux/ftrace.h

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