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linux-next/arch/arc/Makefile
Vineet Gupta a69fe1a2c9 ARC: build: Turn off -Wmaybe-uninitialized for ARC gcc 4.8 
linux-next has been reporting gazillion warnings for ARC build and
I finally decided to take a bite:

http://kisskb.ellerman.id.au/kisskb/buildresult/12638735/

Most of the them are due to -Wmaybe-uninitialized

| ../kernel/sysctl.c: In function '__do_proc_doulongvec_minmax':
| ../kernel/sysctl.c:1928:12: warning: 'p' may be used uninitialized in this function [-Wmaybe-uninitialized]
|   ret = tmp - *buf;
|            ^
| ../kernel/sysctl.c:2342:29: note: 'p' was declared here
|  char *kbuf = NULL, *p;
|                     ^
| ...
| ...

Cursory look at code seemed fine and a definite gcc false positive in say
kernel/sysctl.c

Mystery was why only for ARC (and not with ARM linaro toolchain based
off same gcc 4.8). Turns out that -O3 (default for ARC) triggers these
and if I enable -O3 for ARM kernel build, I see the same splat.

I initially wanted to disable this only for gcc 4.8, but Arnd reported
it is seen even on gcc 6.0 for ARM with -O3. Thus better to disable
this independent of gcc version.

Cc: Claudiu Zissulescu <Claudiu.Zissulescu@synopsys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: linux-kbuild@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
2016-03-18 16:22:36 +05:30

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Makefile
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#
# Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License version 2 as
# published by the Free Software Foundation.
#
UTS_MACHINE := arc
ifeq ($(CROSS_COMPILE),)
ifndef CONFIG_CPU_BIG_ENDIAN
CROSS_COMPILE := arc-linux-
else
CROSS_COMPILE := arceb-linux-
endif
endif
KBUILD_DEFCONFIG := nsim_700_defconfig
cflags-y += -fno-common -pipe -fno-builtin -D__linux__
cflags-$(CONFIG_ISA_ARCOMPACT) += -mA7
cflags-$(CONFIG_ISA_ARCV2) += -mcpu=archs
is_700 = $(shell $(CC) -dM -E - < /dev/null | grep -q "ARC700" && echo 1 || echo 0)
ifdef CONFIG_ISA_ARCOMPACT
ifeq ($(is_700), 0)
$(error Toolchain not configured for ARCompact builds)
endif
endif
ifdef CONFIG_ISA_ARCV2
ifeq ($(is_700), 1)
$(error Toolchain not configured for ARCv2 builds)
endif
endif
ifdef CONFIG_ARC_CURR_IN_REG
# For a global register defintion, make sure it gets passed to every file
# We had a customer reported bug where some code built in kernel was NOT using
# any kernel headers, and missing the r25 global register
# Can't do unconditionally because of recursive include issues
# due to <linux/thread_info.h>
LINUXINCLUDE += -include ${src}/arch/arc/include/asm/current.h
endif
upto_gcc44 := $(call cc-ifversion, -le, 0404, y)
atleast_gcc44 := $(call cc-ifversion, -ge, 0404, y)
atleast_gcc48 := $(call cc-ifversion, -ge, 0408, y)
cflags-$(atleast_gcc44) += -fsection-anchors
cflags-$(CONFIG_ARC_HAS_LLSC) += -mlock
cflags-$(CONFIG_ARC_HAS_SWAPE) += -mswape
ifdef CONFIG_ISA_ARCV2
ifndef CONFIG_ARC_HAS_LL64
cflags-y += -mno-ll64
endif
ifndef CONFIG_ARC_HAS_DIV_REM
cflags-y += -mno-div-rem
endif
endif
cflags-$(CONFIG_ARC_DW2_UNWIND) += -fasynchronous-unwind-tables
# By default gcc 4.8 generates dwarf4 which kernel unwinder can't grok
ifeq ($(atleast_gcc48),y)
cflags-$(CONFIG_ARC_DW2_UNWIND) += -gdwarf-2
endif
ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE
# Generic build system uses -O2, we want -O3
# Note: No need to add to cflags-y as that happens anyways
#
# Disable the false maybe-uninitialized warings gcc spits out at -O3
ARCH_CFLAGS += -O3 $(call cc-disable-warning,maybe-uninitialized,)
endif
# small data is default for elf32 tool-chain. If not usable, disable it
# This also allows repurposing GP as scratch reg to gcc reg allocator
disable_small_data := y
cflags-$(disable_small_data) += -mno-sdata -fcall-used-gp
cflags-$(CONFIG_CPU_BIG_ENDIAN) += -mbig-endian
ldflags-$(CONFIG_CPU_BIG_ENDIAN) += -EB
# STAR 9000518362: (fixed with binutils shipping with gcc 4.8)
# arc-linux-uclibc-ld (buildroot) or arceb-elf32-ld (EZChip) don't accept
# --build-id w/o "-marclinux". Default arc-elf32-ld is OK
ldflags-$(upto_gcc44) += -marclinux
LIBGCC := $(shell $(CC) $(cflags-y) --print-libgcc-file-name)
# Modules with short calls might break for calls into builtin-kernel
KBUILD_CFLAGS_MODULE += -mlong-calls -mno-millicode
# Finally dump eveything into kernel build system
KBUILD_CFLAGS += $(cflags-y)
KBUILD_AFLAGS += $(KBUILD_CFLAGS)
LDFLAGS += $(ldflags-y)
head-y := arch/arc/kernel/head.o
# See arch/arc/Kbuild for content of core part of the kernel
core-y += arch/arc/
# w/o this dtb won't embed into kernel binary
core-y += arch/arc/boot/dts/
core-$(CONFIG_ARC_PLAT_SIM) += arch/arc/plat-sim/
core-$(CONFIG_ARC_PLAT_TB10X) += arch/arc/plat-tb10x/
core-$(CONFIG_ARC_PLAT_AXS10X) += arch/arc/plat-axs10x/
drivers-$(CONFIG_OPROFILE) += arch/arc/oprofile/
libs-y += arch/arc/lib/ $(LIBGCC)
boot := arch/arc/boot
#default target for make without any arguements.
KBUILD_IMAGE := bootpImage
all: $(KBUILD_IMAGE)
bootpImage: vmlinux
boot_targets += uImage uImage.bin uImage.gz
$(boot_targets): vmlinux
$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
%.dtb %.dtb.S %.dtb.o: scripts
$(Q)$(MAKE) $(build)=$(boot)/dts $(boot)/dts/$@
dtbs: scripts
$(Q)$(MAKE) $(build)=$(boot)/dts
archclean:
$(Q)$(MAKE) $(clean)=$(boot)
# Hacks to enable final link due to absence of link-time branch relexation
# and gcc choosing optimal(shorter) branches at -O3
#
# vineetg Feb 2010: -mlong-calls switched off for overall kernel build
# However lib/decompress_inflate.o (.init.text) calls
# zlib_inflate_workspacesize (.text) causing relocation errors.
# Thus forcing all exten calls in this file to be long calls
export CFLAGS_decompress_inflate.o = -mmedium-calls
export CFLAGS_initramfs.o = -mmedium-calls
ifdef CONFIG_SMP
export CFLAGS_core.o = -mmedium-calls
endif
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