linux-kernel - [PATCH] ARM: atags_to_fdt: don't warn about stack size

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Date:   Mon,  9 Aug 2021 17:10:21 +0200
From:   David Heidelberg <david@...t.cz>
To:     Arnd Bergmann <arnd@...db.de>, Jon Medhurst <tixy@...aro.org>,
        Russell King <linux@....linux.org.uk>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Nicolas Pitre <nico@...aro.org>
Cc:     David Heidelberg <david@...t.cz>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH] ARM: atags_to_fdt: don't warn about stack size

The merge_fdt_bootargs() function by definition consumes more than 1024
bytes of stack because it has a 1024 byte command line on the stack,
meaning that we always get a warning when building this file:

arch/arm/boot/compressed/atags_to_fdt.c: In function 'merge_fdt_bootargs':
arch/arm/boot/compressed/atags_to_fdt.c:98:1: warning: the frame size of 1032 bytes is larger than 1024 bytes [-Wframe-larger-than=]

However, as this is the decompressor and we know that it has a very shallow
call chain, and we do not actually risk overflowing the kernel stack
at runtime here.

This just shuts up the warning by disabling the warning flag for this
file.

Tested on Nexus 7 2012 builds.

Original Author: Arnd Bergmann <arnd@...db.de>
Reference: https://lore.kernel.org/lkml/8232115.18ykgQ6J5T@wuerfel/

Cc: Arnd Bergmann <arnd@...db.de>
Cc: Nicolas Pitre <nico@...aro.org>
Cc: Russell King <linux@....linux.org.uk>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc: Marc Zyngier <marc.zyngier@....com>
Cc: linux-kernel@...r.kernel.org
Cc: linux-arm-kernel@...ts.infradead.org

Signed-off-by: David Heidelberg <david@...t.cz>
---
 arch/arm/boot/compressed/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index 9d91ae1091b0..91265e7ff672 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -85,6 +85,8 @@ compress-$(CONFIG_KERNEL_LZ4)  = lz4
 libfdt_objs := fdt_rw.o fdt_ro.o fdt_wip.o fdt.o
 
 ifeq ($(CONFIG_ARM_ATAG_DTB_COMPAT),y)
+CFLAGS_REMOVE_atags_to_fdt.o += -Wframe-larger-than=${CONFIG_FRAME_WARN}
+CFLAGS_atags_to_fdt.o += -Wframe-larger-than=1280
 OBJS	+= $(libfdt_objs) atags_to_fdt.o
 endif
 ifeq ($(CONFIG_USE_OF),y)
-- 
2.30.2