[RFC PATCH v3 02/17] unwind_user/fp: Use dummies instead of ifdef

Jens Remus
2025-12-08T17:16:38Z

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@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 f9a1c460150d..a528eee80dd6 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -37,6 +37,7 @@ 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 7f7282516bf5..64618618febd 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 f81c36ab2861..fdb1001e3750 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -74,7 +74,6 @@ 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)) {
@@ -88,9 +87,6 @@ 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_sframe(struct unwind_user_state *state)
--
2.51.0