[PATCH 0/2] riscv: ftrace: use frame CFA as the function graph retp identity

[Rui Qi]

RISC-V dynamic function graph tracing currently saves &fregs->ra as the
graph retp -- the lookup key that ftrace_graph_ret_addr() matches against
shadow stack entries. That address points into ftrace_caller's temporary
fregs frame, which disappears once ftrace_caller returns. Later stack
unwinding finds return_to_handler in the traced function's own frame and
looks it up with the frame CFA, so the saved entry can never match. The
same mismatch breaks function_get_true_parent_ip(), which looks up the
original parent with the saved entry SP rather than &fregs->ra.

Patch 1 clarifies the ftrace_graph_ret_addr() documentation: retp is
compared, not dereferenced, and may be any stable frame identity as long
as the graph entry path and the unwinder use the same value. 

Patch 2 makes RISC-V use the frame CFA for that identity: the static _mcount
path derives it from &frame->ra, the dynamic ftrace path uses the saved
entry SP, and the frame-pointer unwinder tracks the same CFA when
recovering graph return addresses.

Build-tested for rv64 with gcc and clang (full vmlinux).

Rui Qi (2):
  ftrace: Clarify function graph retp identity
  riscv: ftrace: Use frame CFA for function graph retp

 arch/riscv/kernel/ftrace.c     | 10 ++++++++--
 arch/riscv/kernel/stacktrace.c |  2 +-
 kernel/trace/fgraph.c          |  7 +++++--
 3 files changed, 14 insertions(+), 5 deletions(-)

-- 
2.20.1