linux-kernel - [PATCH 1/3] unwind_user: Enhance comments on get CFA, FP, and RA

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Message-ID: <20251125164349.2592874-2-jremus@linux.ibm.com>
Date: Tue, 25 Nov 2025 17:43:47 +0100
From: Jens Remus <jremus@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
        x86@...nel.org, Steven Rostedt <rostedt@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc: Jens Remus <jremus@...ux.ibm.com>, Josh Poimboeuf <jpoimboe@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Indu Bhagat <indu.bhagat@...cle.com>,
        "Jose E. Marchesi" <jemarch@....org>,
        Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Ilya Leoshkevich <iii@...ux.ibm.com>
Subject: [PATCH 1/3] 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>
---
 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 39e270789444..0ca434f86e73 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;
 
-- 
2.51.0