On Tue, 17 May 2022 03:18:34 -0400 Xu Kuohai xukuohai@huawei.com wrote:
After direct call is enabled for arm64, ftrace selftest enters a dead loop:
<trace_selftest_dynamic_test_func>: 00 bti c 01 mov x9, x30 <trace_direct_tramp>: 02 bl <trace_direct_tramp> ----------> ret | lr/x30 is 03, return to 03 | 03 mov w0, #0x0 <-----------------------------| | | | dead loop! | | | 04 ret ---- lr/x30 is still 03, go back to 03 ----|
The reason is that when the direct caller trace_direct_tramp() returns to the patched function trace_selftest_dynamic_test_func(), lr is still the address after the instrumented instruction in the patched function, so when the patched function exits, it returns to itself!
To fix this issue, we need to restore lr before trace_direct_tramp() exits, so rewrite a dedicated trace_direct_tramp() for arm64.
Reported-by: Li Huafei lihuafei1@huawei.com Signed-off-by: Xu Kuohai xukuohai@huawei.com
Acked-by: Steven Rostedt (Google) rostedt@goodmis.org
-- Steve