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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 06/37] pinctrl: ingenic: Improve unreachable code generation
Date: Thu, 20 May 2021 11:22:27 +0200	[thread overview]
Message-ID: <20210520092052.474597254@linuxfoundation.org> (raw)
In-Reply-To: <20210520092052.265851579@linuxfoundation.org>

From: Josh Poimboeuf <jpoimboe@redhat.com>

[ Upstream commit d6d43a92172085a2681e06a0d06aac53c7bcdd12 ]

In the second loop of ingenic_pinconf_set(), it annotates the switch
default case as unreachable().  The annotation is technically correct,
because that same case would have resulted in an early function return
in the previous loop.

However, the compiled code is suboptimal.  GCC seems to work extra hard
to ensure that the unreachable code path triggers undefined behavior.
The function would fall through to start executing whatever function
happens to be next in the compilation unit.

This is problematic because:

  a) it adds unnecessary 'ensure undefined behavior' logic, and
     corresponding i-cache footprint; and

  b) it's less robust -- if a bug were to be introduced, falling through
     to the next function would be catastrophic.

Yet another issue is that, while objtool normally understands
unreachable() annotations, there's one special case where it doesn't:
when the annotation occurs immediately after a 'ret' instruction.  That
happens to be the case here because unreachable() is immediately before
the return.

Remove the unreachable() annotation and replace it with a comment.  This
simplifies the code generation and changes the unreachable error path to
just silently return instead of corrupting execution.

This fixes the following objtool warning:

  drivers/pinctrl/pinctrl-ingenic.o: warning: objtool: ingenic_pinconf_set() falls through to next function ingenic_pinconf_group_set()

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/bc20fdbcb826512cf76b7dfd0972740875931b19.1582212881.git.jpoimboe@redhat.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/pinctrl/pinctrl-ingenic.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/pinctrl/pinctrl-ingenic.c b/drivers/pinctrl/pinctrl-ingenic.c
index 61e7d938d4c5..91596eee0bda 100644
--- a/drivers/pinctrl/pinctrl-ingenic.c
+++ b/drivers/pinctrl/pinctrl-ingenic.c
@@ -1846,7 +1846,8 @@ static int ingenic_pinconf_set(struct pinctrl_dev *pctldev, unsigned int pin,
 			break;
 
 		default:
-			unreachable();
+			/* unreachable */
+			break;
 		}
 	}
 
-- 
2.30.2




  parent reply	other threads:[~2021-05-20  9:33 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-20  9:22 [PATCH 5.4 00/37] 5.4.121-rc1 review Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 01/37] x86/msr: Fix wr/rdmsr_safe_regs_on_cpu() prototypes Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 02/37] kgdb: fix gcc-11 warning on indentation Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 03/37] usb: sl811-hcd: improve misleading indentation Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 04/37] cxgb4: Fix the -Wmisleading-indentation warning Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 05/37] isdn: capi: fix mismatched prototypes Greg Kroah-Hartman
2021-05-20  9:22 ` Greg Kroah-Hartman [this message]
2021-05-20  9:22 ` [PATCH 5.4 07/37] xsk: Simplify detection of empty and full rings Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 08/37] virtio_net: Do not pull payload in skb->head Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 09/37] ARM: 9058/1: cache-v7: refactor v7_invalidate_l1 to avoid clobbering r5/r6 Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 10/37] PCI: thunder: Fix compile testing Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 11/37] dmaengine: dw-edma: Fix crash on loading/unloading driver Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 12/37] ARM: 9066/1: ftrace: pause/unpause function graph tracer in cpu_suspend() Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 13/37] ACPI / hotplug / PCI: Fix reference count leak in enable_slot() Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 14/37] Input: elants_i2c - do not bind to i2c-hid compatible ACPI instantiated devices Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 15/37] Input: silead - add workaround for x86 BIOS-es which bring the chip up in a stuck state Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 16/37] um: Mark all kernel symbols as local Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 17/37] um: Disable CONFIG_GCOV with MODULES Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 18/37] ARM: 9075/1: kernel: Fix interrupted SMC calls Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 19/37] scripts/recordmcount.pl: Fix RISC-V regex for clang Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 20/37] riscv: Workaround mcount name prior to clang-13 Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 21/37] scsi: lpfc: Fix illegal memory access on Abort IOCBs Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 22/37] ceph: fix fscache invalidation Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 23/37] scsi: target: tcmu: Return from tcmu_handle_completions() if cmd_id not found Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 24/37] bridge: Fix possible races between assigning rx_handler_data and setting IFF_BRIDGE_PORT bit Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 25/37] drm/amd/display: Fix two cursor duplication when using overlay Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 26/37] gpiolib: acpi: Add quirk to ignore EC wakeups on Dell Venue 10 Pro 5055 Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 27/37] ALSA: hda: generic: change the DAC ctl name for LO+SPK or LO+HP Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 28/37] block: reexpand iov_iter after read/write Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 29/37] lib: stackdepot: turn depot_lock spinlock to raw_spinlock Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 30/37] net: stmmac: Do not enable RX FIFO overflow interrupts Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 31/37] ip6_gre: proper dev_{hold|put} in ndo_[un]init methods Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 32/37] sit: " Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 33/37] ip6_tunnel: " Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 34/37] ipv6: remove extra dev_hold() for fallback tunnels Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 35/37] KVM: arm64: Initialize VCPU mdcr_el2 before loading it Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 36/37] tweewide: Fix most Shebang lines Greg Kroah-Hartman
2021-05-20  9:22 ` [PATCH 5.4 37/37] scripts: switch explicitly to Python 3 Greg Kroah-Hartman
2021-05-20 21:44 ` [PATCH 5.4 00/37] 5.4.121-rc1 review Shuah Khan
2021-05-20 22:53 ` Guenter Roeck
2021-05-21  4:39 ` Florian Fainelli
2021-05-22  9:39   ` Greg Kroah-Hartman
2021-05-21  5:23 ` Naresh Kamboju
2021-05-21 18:21 ` Sudip Mukherjee

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