linux-kernel - [tip: perf/core] unwind_user/fp: Use dummies instead of ifdef

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Message-ID: <176597508428.510.17923884239996413306.tip-bot2@tip-bot2>
Date: Wed, 17 Dec 2025 12:38:04 -0000
From: "tip-bot2 for Jens Remus" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Jens Remus <jremus@...ux.ibm.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: perf/core] unwind_user/fp: Use dummies instead of ifdef

The following commit has been merged into the perf/core branch of tip:

Commit-ID:     2652f9a4b019e34fbbde8dcd1396f1f00ec4844f
Gitweb:        https://git.kernel.org/tip/2652f9a4b019e34fbbde8dcd1396f1f00ec4844f
Author:        Jens Remus <jremus@...ux.ibm.com>
AuthorDate:    Mon, 08 Dec 2025 17:03:50 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 17 Dec 2025 13:31:07 +01:00

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.

Provide (1) a dummy definition of ARCH_INIT_USER_FP_FRAME, if the unwind
user method HAVE_UNWIND_USER_FP is not enabled, (2) a common fallback
definition of unwind_user_at_function_start() which returns false, and
(3) a common dummy definition of ARCH_INIT_USER_FP_ENTRY_FRAME.

Note that enabling the config option HAVE_UNWIND_USER_FP without
defining ARCH_INIT_USER_FP_FRAME triggers a compile error, which is
helpful when implementing support for this unwind user method in an
architecture.  Enabling the config option when providing an arch-
specific unwind_user_at_function_start() definition makes it necessary
to also provide an arch-specific ARCH_INIT_USER_FP_ENTRY_FRAME
definition.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://patch.msgid.link/20251208160352.1363040-3-jremus@linux.ibm.com
---
 arch/x86/include/asm/unwind_user.h |  1 +
 include/linux/unwind_user.h        | 18 ++++++++++++++++--
 kernel/unwind/user.c               |  4 ----
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index 1206428..971ffe9 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -35,6 +35,7 @@ static inline bool unwind_user_at_function_start(struct pt_regs *regs)
 {
 	return is_uprobe_at_func_entry(regs);
 }
+#define unwind_user_at_function_start unwind_user_at_function_start
 
 #endif /* CONFIG_HAVE_UNWIND_USER_FP */
 
diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index 7f72825..6461861 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -5,8 +5,22 @@
 #include <linux/unwind_user_types.h>
 #include <asm/unwind_user.h>
 
-#ifndef ARCH_INIT_USER_FP_FRAME
- #define ARCH_INIT_USER_FP_FRAME
+#ifndef CONFIG_HAVE_UNWIND_USER_FP
+
+#define ARCH_INIT_USER_FP_FRAME(ws)
+
+#endif
+
+#ifndef ARCH_INIT_USER_FP_ENTRY_FRAME
+#define ARCH_INIT_USER_FP_ENTRY_FRAME(ws)
+#endif
+
+#ifndef unwind_user_at_function_start
+static inline bool unwind_user_at_function_start(struct pt_regs *regs)
+{
+	return false;
+}
+#define unwind_user_at_function_start unwind_user_at_function_start
 #endif
 
 int unwind_user(struct unwind_stacktrace *trace, unsigned int max_entries);
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 0ca434f..90ab3c1 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)