linux-kernel - [PATCH 2/3] unwind_user/fp: Use dummies instead of ifdef

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Message-ID: <20251125164349.2592874-3-jremus@linux.ibm.com>
Date: Tue, 25 Nov 2025 17:43:48 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        x86@...nel.org, Steven Rostedt <rostedt@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: [PATCH 2/3] unwind_user/fp: Use dummies instead of ifdef

This simplifies the code.   unwind_user_next_fp() does not need to
return -EINVAL if config option HAVE_UNWIND_USER_FP is disabled, as
unwind_user_start() will then not select this unwind method and
unwind_user_next() will therefore not call it.

Note that enabling the config option HAVE_UNWIND_USER_FP without
defining ARCH_INIT_USER_FP_FRAME, ARCH_INIT_USER_FP_ENTRY_FRAME, and
unwind_user_at_function_start() will result in a compile error, which
is helpful when implementing support for unwind user fp in an
architecture.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
---
 include/linux/unwind_user.h | 14 +++++++++++---
 kernel/unwind/user.c        |  4 ----
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index 7f7282516bf5..c3ff690a43e2 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -5,9 +5,17 @@
 #include <linux/unwind_user_types.h>
 #include <asm/unwind_user.h>
 
-#ifndef ARCH_INIT_USER_FP_FRAME
- #define ARCH_INIT_USER_FP_FRAME
-#endif
+#ifndef CONFIG_HAVE_UNWIND_USER_FP
+
+#define ARCH_INIT_USER_FP_FRAME
+#define ARCH_INIT_USER_FP_ENTRY_FRAME
+
+static inline bool unwind_user_at_function_start(struct pt_regs *regs)
+{
+	return false;
+}
+
+#endif /* !CONFIG_HAVE_UNWIND_USER_FP */
 
 int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries);
 
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 0ca434f86e73..90ab3c1a205e 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -67,7 +67,6 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 
 static int unwind_user_next_fp(struct unwind_user_state *state)
 {
-#ifdef CONFIG_HAVE_UNWIND_USER_FP
 	struct pt_regs *regs = task_pt_regs(current);
 
 	if (state->topmost && unwind_user_at_function_start(regs)) {
@@ -81,9 +80,6 @@ static int unwind_user_next_fp(struct unwind_user_state *state)
 		ARCH_INIT_USER_FP_FRAME(state->ws)
 	};
 	return unwind_user_next_common(state, &fp_frame);
-#else
-	return -EINVAL;
-#endif
 }
 
 static int unwind_user_next(struct unwind_user_state *state)
-- 
2.51.0