linux-kernel - [tip: perf/core] unwind_user: Enhance comments on get CFA, FP, and RA

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Message-ID: <176597508521.510.9459757707168769746.tip-bot2@tip-bot2>
Date: Wed, 17 Dec 2025 12:38:05 -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: Enhance comments on get CFA, FP, and RA

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

Commit-ID:     2d6ad925fb2386f3ee1d26f5022f7ea71bbc1541
Gitweb:        https://git.kernel.org/tip/2d6ad925fb2386f3ee1d26f5022f7ea71bbc1541
Author:        Jens Remus <jremus@...ux.ibm.com>
AuthorDate:    Mon, 08 Dec 2025 17:03:49 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Wed, 17 Dec 2025 13:31:07 +01:00

unwind_user: Enhance comments on get CFA, FP, and RA

Move the comment "Get the Canonical Frame Address (CFA)" to the top
of the sequence of statements that actually get the CFA.  Reword the
comment "Find the Return Address (RA)" to "Get ...", as the statements
actually get the RA.  Add a respective comment to the statements that
get the FP.  This will be useful once future commits extend the logic
to get the RA and FP.

While at it align the comment on the "stack going in wrong direction"
check to the following one on the "address is word aligned" check.

Signed-off-by: Jens Remus <jremus@...ux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://patch.msgid.link/20251208160352.1363040-2-jremus@linux.ibm.com
---
 kernel/unwind/user.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/unwind/user.c b/kernel/unwind/user.c
index 39e2707..0ca434f 100644
--- a/kernel/unwind/user.c
+++ b/kernel/unwind/user.c
@@ -31,6 +31,7 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 {
 	unsigned long cfa, fp, ra;
 
+	/* Get the Canonical Frame Address (CFA) */
 	if (frame->use_fp) {
 		if (state->fp < state->sp)
 			return -EINVAL;
@@ -38,11 +39,9 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 	} else {
 		cfa = state->sp;
 	}
-
-	/* Get the Canonical Frame Address (CFA) */
 	cfa += frame->cfa_off;
 
-	/* stack going in wrong direction? */
+	/* Make sure that stack is not going in wrong direction */
 	if (cfa <= state->sp)
 		return -EINVAL;
 
@@ -50,10 +49,11 @@ static int unwind_user_next_common(struct unwind_user_state *state,
 	if (cfa & (state->ws - 1))
 		return -EINVAL;
 
-	/* Find the Return Address (RA) */
+	/* Get the Return Address (RA) */
 	if (get_user_word(&ra, cfa, frame->ra_off, state->ws))
 		return -EINVAL;
 
+	/* Get the Frame Pointer (FP) */
 	if (frame->fp_off && get_user_word(&fp, cfa, frame->fp_off, state->ws))
 		return -EINVAL;