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unwind_user/fp: Use dummies instead of ifdef

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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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251208160352.1363040-3-jremus@linux.ibm.com
This commit is contained in:
Jens Remus 2025-12-08 17:03:50 +01:00 • committed by Peter Zijlstra
parent 2d6ad925fb
commit 2652f9a4b0
3 changed files with 17 additions and 6 deletions
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1
arch/x86/include/asm/unwind_user.h
View file

@ -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 */

18
include/linux/unwind_user.h
View file

@ -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);

4
kernel/unwind/user.c
View file

@ -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)