[PATCH v11 02/14] unwind_user: Add frame pointer support

[Steven Rostedt <rostedt@goodmis.org>]

From: Josh Poimboeuf <jpoimboe@kernel.org>

Add optional support for user space frame pointer unwinding.  If
supported, the arch needs to enable CONFIG_HAVE_UNWIND_USER_FP and
define ARCH_INIT_USER_FP_FRAME.

By encoding the frame offsets in struct unwind_user_frame, much of this
code can also be reused for future unwinder implementations like sframe.

Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Co-developed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v10: https://lore.kernel.org/20250611010428.092934995@goodmis.org

- Rename "the_end" label to "done" to be more consistent to what the
  kernel uses. (Peter Zijlstra)

- Add a comment about what cfa and ra stand for. (Peter Zijlstra)

 arch/Kconfig                      |  4 +++
 include/asm-generic/Kbuild        |  1 +
 include/asm-generic/unwind_user.h |  5 +++
 include/linux/unwind_user.h       |  5 +++
 include/linux/unwind_user_types.h |  1 +
 kernel/unwind/user.c              | 51 +++++++++++++++++++++++++++++--
 6 files changed, 65 insertions(+), 2 deletions(-)
 create mode 100644 include/asm-generic/unwind_user.h

diff --git a/arch/Kconfig b/arch/Kconfig
index ea59e5d7cc69..8e3fd723bd74 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -438,6 +438,10 @@ config HAVE_HARDLOCKUP_DETECTOR_ARCH
 config UNWIND_USER
 	bool
 
+config HAVE_UNWIND_USER_FP
+	bool
+	select UNWIND_USER
+
 config HAVE_PERF_REGS
 	bool
 	help
diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index 8675b7b4ad23..295c94a3ccc1 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -59,6 +59,7 @@ mandatory-y += tlbflush.h
 mandatory-y += topology.h
 mandatory-y += trace_clock.h
 mandatory-y += uaccess.h
+mandatory-y += unwind_user.h
 mandatory-y += vermagic.h
 mandatory-y += vga.h
 mandatory-y += video.h
diff --git a/include/asm-generic/unwind_user.h b/include/asm-generic/unwind_user.h
new file mode 100644
index 000000000000..b8882b909944
--- /dev/null
+++ b/include/asm-generic/unwind_user.h
@@ -0,0 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_UNWIND_USER_H
+#define _ASM_GENERIC_UNWIND_USER_H
+
+#endif /* _ASM_GENERIC_UNWIND_USER_H */
diff --git a/include/linux/unwind_user.h b/include/linux/unwind_user.h
index aa7923c1384f..a405111c41b0 100644
--- a/include/linux/unwind_user.h
+++ b/include/linux/unwind_user.h
@@ -3,6 +3,11 @@
 #define _LINUX_UNWIND_USER_H
 
 #include <linux/unwind_user_types.h>
+#include <asm/unwind_user.h>
+
+#ifndef ARCH_INIT_USER_FP_FRAME
+ #define ARCH_INIT_USER_FP_FRAME
+#endif
 
 int unwind_user_start(struct unwind_user_state *state);
 int unwind_user_next(struct unwind_user_state *state);
diff --git a/include/linux/unwind_user_types.h b/include/linux/unwind_user_types.h
index 6ed1b4ae74e1..65bd070eb6b0 100644
--- a/include/linux/unwind_user_types.h
+++ b/include/linux/unwind_user_types.h
@@ -6,6 +6,7 @@
 
 enum unwind_user_type {
 	UNWIND_USER_TYPE_NONE,
+	UNWIND_USER_TYPE_FP,
 };
 
 struct unwind_stacktrace {
diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index d30449328981..1201d655654a 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -6,10 +6,54 @@
 #include <linux/sched.h>
 #include <linux/sched/task_stack.h>
 #include <linux/unwind_user.h>
+#include <linux/uaccess.h>
+
+static struct unwind_user_frame fp_frame = {
+	ARCH_INIT_USER_FP_FRAME
+};
+
+static inline bool fp_state(struct unwind_user_state *state)
+{
+	return IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP) &&
+	       state->type == UNWIND_USER_TYPE_FP;
+}
 
 int unwind_user_next(struct unwind_user_state *state)
 {
-	/* no implementation yet */
+	struct unwind_user_frame *frame;
+	unsigned long cfa = 0, fp, ra = 0;
+
+	if (state->done)
+		return -EINVAL;
+
+	if (fp_state(state))
+		frame = &fp_frame;
+	else
+		goto done;
+
+	/* Get the Canonical Frame Address (CFA) */
+	cfa = (frame->use_fp ? state->fp : state->sp) + frame->cfa_off;
+
+	/* stack going in wrong direction? */
+	if (cfa <= state->sp)
+		goto done;
+
+	/* Find the Return Address (RA) */
+	if (get_user(ra, (unsigned long *)(cfa + frame->ra_off)))
+		goto done;
+
+	if (frame->fp_off && get_user(fp, (unsigned long __user *)(cfa + frame->fp_off)))
+		goto done;
+
+	state->ip = ra;
+	state->sp = cfa;
+	if (frame->fp_off)
+		state->fp = fp;
+
+	return 0;
+
+done:
+	state->done = true;
 	return -EINVAL;
 }
 
@@ -24,7 +68,10 @@ int unwind_user_start(struct unwind_user_state *state)
 		return -EINVAL;
 	}
 
-	state->type = UNWIND_USER_TYPE_NONE;
+	if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP))
+		state->type = UNWIND_USER_TYPE_FP;
+	else
+		state->type = UNWIND_USER_TYPE_NONE;
 
 	state->ip = instruction_pointer(regs);
 	state->sp = user_stack_pointer(regs);
-- 
2.47.2