linux-kernel - [PATCH 20/22] regulator: rk808: Remove undefined behavior in rk806_set_mode

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Message-ID: <2023abcddf3f524ba478d64339996f25dc4097d2.1742852847.git.jpoimboe@kernel.org>
Date: Mon, 24 Mar 2025 14:56:10 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: x86@...nel.org
Cc: linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Miroslav Benes <mbenes@...e.cz>,
	Brendan Jackman <jackmanb@...gle.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Mark Brown <broonie@...nel.org>,
	kernel test robot <lkp@...el.com>
Subject: [PATCH 20/22] regulator: rk808: Remove undefined behavior in rk806_set_mode_dcdc()

If ctr_bit is negative, the shift counts become negative, causing a
shift of bounds and undefined behavior.

Presumably that's not possible in normal operation, but the code
generation isn't optimal.  And undefined behavior should be avoided
regardless.

Improve code generation and remove the undefined behavior by converting
the signed variables to unsigned.

Fixes the following warning with an UBSAN kernel:

  vmlinux.o: warning: objtool: rk806_set_mode_dcdc() falls through to next function rk806_get_mode_dcdc()
  vmlinux.o: warning: objtool: .text.rk806_set_mode_dcdc: unexpected end of section

Cc: Liam Girdwood <lgirdwood@...il.com>
Cc: Mark Brown <broonie@...nel.org>
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202503182350.52KeHGD4-lkp@intel.com/
Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
---
 drivers/regulator/rk808-regulator.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/regulator/rk808-regulator.c b/drivers/regulator/rk808-regulator.c
index 7d82bd1b36df..1e8142479656 100644
--- a/drivers/regulator/rk808-regulator.c
+++ b/drivers/regulator/rk808-regulator.c
@@ -270,8 +270,8 @@ static const unsigned int rk817_buck1_4_ramp_table[] = {
 
 static int rk806_set_mode_dcdc(struct regulator_dev *rdev, unsigned int mode)
 {
-	int rid = rdev_get_id(rdev);
-	int ctr_bit, reg;
+	unsigned int rid = rdev_get_id(rdev);
+	unsigned int ctr_bit, reg;
 
 	reg = RK806_POWER_FPWM_EN0 + rid / 8;
 	ctr_bit = rid % 8;
-- 
2.48.1