[PATCH 1/2] arm64: ftrace: enable single ftrace_ops for direct calls

[Leon Hwang <leon.hwang@linux.dev>]

The BPF tracing multi link updates several direct-call sites through one
ftrace_ops. Its implementation is therefore gated by
HAVE_SINGLE_FTRACE_DIRECT_OPS in addition to
DYNAMIC_FTRACE_WITH_DIRECT_CALLS.

Select HAVE_SINGLE_FTRACE_DIRECT_OPS whenever arm64 enables dynamic ftrace
direct calls. This enables BPF tracing multi links on arm64. Also
generalize the unreachable-trampoline comment because the single-ops path
does not use ops->direct_call.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 arch/arm64/Kconfig         | 2 ++
 arch/arm64/kernel/ftrace.c | 3 +--
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0de419ed780f..c98dca76859b 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -188,6 +188,8 @@ config ARM64
 		    CLANG_SUPPORTS_DYNAMIC_FTRACE_WITH_ARGS)
 	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS \
 		if DYNAMIC_FTRACE_WITH_ARGS
+	select HAVE_SINGLE_FTRACE_DIRECT_OPS \
+		if DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 	select HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS \
 		if (DYNAMIC_FTRACE_WITH_ARGS && !CFI && \
 		    (CC_IS_CLANG || !CC_OPTIMIZE_FOR_SIZE))
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c
index e1a3c0b3a051..56ba72a87dfa 100644
--- a/arch/arm64/kernel/ftrace.c
+++ b/arch/arm64/kernel/ftrace.c
@@ -301,8 +301,7 @@ static bool ftrace_find_callable_addr(struct dyn_ftrace *rec,
 
 	/*
 	 * If a custom trampoline is unreachable, rely on the ftrace_caller
-	 * trampoline which knows how to indirectly reach that trampoline
-	 * through ops->direct_call.
+	 * trampoline which knows how to indirectly reach that trampoline.
 	 */
 	if (*addr != FTRACE_ADDR && !reachable_by_bl(*addr, pc))
 		*addr = FTRACE_ADDR;
-- 
2.55.0