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https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
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a76bcf557e
Traditionally, we have always had warnings about uninitialized variables enabled, as this is part of -Wall, and generally a good idea [1], but it also always produced false positives, mainly because this is a variation of the halting problem and provably impossible to get right in all cases [2]. Various people have identified cases that are particularly bad for false positives, and in commite74fc973b6("Turn off -Wmaybe-uninitialized when building with -Os"), I turned off the warning for any build that was done with CC_OPTIMIZE_FOR_SIZE. This drastically reduced the number of false positive warnings in the default build but unfortunately had the side effect of turning the warning off completely in 'allmodconfig' builds, which in turn led to a lot of warnings (both actual bugs, and remaining false positives) to go in unnoticed. With commit877417e6ff("Kbuild: change CC_OPTIMIZE_FOR_SIZE definition") enabled the warning again for allmodconfig builds in v4.7 and in v4.8-rc1, I had finally managed to address all warnings I get in an ARM allmodconfig build and most other maybe-uninitialized warnings for ARM randconfig builds. However, commit6e8d666e92("Disable "maybe-uninitialized" warning globally") was merged at the same time and disabled it completely for all configurations, because of false-positive warnings on x86 that I had not addressed until then. This caused a lot of actual bugs to get merged into mainline, and I sent several dozen patches for these during the v4.9 development cycle. Most of these are actual bugs, some are for correct code that is safe because it is only called under external constraints that make it impossible to run into the case that gcc sees, and in a few cases gcc is just stupid and finds something that can obviously never happen. I have now done a few thousand randconfig builds on x86 and collected all patches that I needed to address every single warning I got (I can provide the combined patch for the other warnings if anyone is interested), so I hope we can get the warning back and let people catch the actual bugs earlier. This reverts the change to disable the warning completely and for now brings it back at the "make W=1" level, so we can get it merged into mainline without introducing false positives. A follow-up patch enables it on all levels unless some configuration option turns it off because of false-positives. Link: https://rusty.ozlabs.org/?p=232 [1] Link: https://gcc.gnu.org/wiki/Better_Uninitialized_Warnings [2] Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
153 lines
4.4 KiB
Makefile
153 lines
4.4 KiB
Makefile
#
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# Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
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#
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# This program is free software; you can redistribute it and/or modify
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# it under the terms of the GNU General Public License version 2 as
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# published by the Free Software Foundation.
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#
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UTS_MACHINE := arc
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ifeq ($(CROSS_COMPILE),)
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ifndef CONFIG_CPU_BIG_ENDIAN
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CROSS_COMPILE := arc-linux-
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else
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CROSS_COMPILE := arceb-linux-
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endif
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endif
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KBUILD_DEFCONFIG := nsim_700_defconfig
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cflags-y += -fno-common -pipe -fno-builtin -D__linux__
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cflags-$(CONFIG_ISA_ARCOMPACT) += -mA7
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cflags-$(CONFIG_ISA_ARCV2) += -mcpu=archs
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is_700 = $(shell $(CC) -dM -E - < /dev/null | grep -q "ARC700" && echo 1 || echo 0)
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ifdef CONFIG_ISA_ARCOMPACT
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ifeq ($(is_700), 0)
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$(error Toolchain not configured for ARCompact builds)
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endif
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endif
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ifdef CONFIG_ISA_ARCV2
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ifeq ($(is_700), 1)
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$(error Toolchain not configured for ARCv2 builds)
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endif
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endif
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ifdef CONFIG_ARC_CURR_IN_REG
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# For a global register defintion, make sure it gets passed to every file
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# We had a customer reported bug where some code built in kernel was NOT using
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# any kernel headers, and missing the r25 global register
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# Can't do unconditionally because of recursive include issues
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# due to <linux/thread_info.h>
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LINUXINCLUDE += -include ${src}/arch/arc/include/asm/current.h
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endif
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upto_gcc44 := $(call cc-ifversion, -le, 0404, y)
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atleast_gcc44 := $(call cc-ifversion, -ge, 0404, y)
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cflags-$(atleast_gcc44) += -fsection-anchors
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ifdef CONFIG_ISA_ARCV2
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ifndef CONFIG_ARC_HAS_LL64
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cflags-y += -mno-ll64
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endif
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ifndef CONFIG_ARC_HAS_DIV_REM
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cflags-y += -mno-div-rem
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endif
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endif
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cfi := $(call as-instr,.cfi_startproc\n.cfi_endproc,-DARC_DW2_UNWIND_AS_CFI)
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cflags-$(CONFIG_ARC_DW2_UNWIND) += -fasynchronous-unwind-tables $(cfi)
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ifndef CONFIG_CC_OPTIMIZE_FOR_SIZE
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# Generic build system uses -O2, we want -O3
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# Note: No need to add to cflags-y as that happens anyways
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#
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# Disable the false maybe-uninitialized warings gcc spits out at -O3
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ARCH_CFLAGS += -O3 $(call cc-disable-warning,maybe-uninitialized,)
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endif
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# small data is default for elf32 tool-chain. If not usable, disable it
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# This also allows repurposing GP as scratch reg to gcc reg allocator
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disable_small_data := y
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cflags-$(disable_small_data) += -mno-sdata -fcall-used-gp
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cflags-$(CONFIG_CPU_BIG_ENDIAN) += -mbig-endian
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ldflags-$(CONFIG_CPU_BIG_ENDIAN) += -EB
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# STAR 9000518362: (fixed with binutils shipping with gcc 4.8)
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# arc-linux-uclibc-ld (buildroot) or arceb-elf32-ld (EZChip) don't accept
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# --build-id w/o "-marclinux". Default arc-elf32-ld is OK
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ldflags-$(upto_gcc44) += -marclinux
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LIBGCC := $(shell $(CC) $(cflags-y) --print-libgcc-file-name)
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# Modules with short calls might break for calls into builtin-kernel
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KBUILD_CFLAGS_MODULE += -mlong-calls -mno-millicode
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# Finally dump eveything into kernel build system
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KBUILD_CFLAGS += $(cflags-y)
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KBUILD_AFLAGS += $(KBUILD_CFLAGS)
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LDFLAGS += $(ldflags-y)
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head-y := arch/arc/kernel/head.o
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# See arch/arc/Kbuild for content of core part of the kernel
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core-y += arch/arc/
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# w/o this dtb won't embed into kernel binary
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core-y += arch/arc/boot/dts/
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core-$(CONFIG_ARC_PLAT_SIM) += arch/arc/plat-sim/
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core-$(CONFIG_ARC_PLAT_TB10X) += arch/arc/plat-tb10x/
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core-$(CONFIG_ARC_PLAT_AXS10X) += arch/arc/plat-axs10x/
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core-$(CONFIG_ARC_PLAT_EZNPS) += arch/arc/plat-eznps/
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ifdef CONFIG_ARC_PLAT_EZNPS
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KBUILD_CPPFLAGS += -I$(srctree)/arch/arc/plat-eznps/include
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endif
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drivers-$(CONFIG_OPROFILE) += arch/arc/oprofile/
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libs-y += arch/arc/lib/ $(LIBGCC)
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boot := arch/arc/boot
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#default target for make without any arguments.
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KBUILD_IMAGE := bootpImage
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all: $(KBUILD_IMAGE)
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bootpImage: vmlinux
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boot_targets += uImage uImage.bin uImage.gz
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$(boot_targets): vmlinux
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$(Q)$(MAKE) $(build)=$(boot) $(boot)/$@
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%.dtb %.dtb.S %.dtb.o: scripts
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$(Q)$(MAKE) $(build)=$(boot)/dts $(boot)/dts/$@
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dtbs: scripts
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$(Q)$(MAKE) $(build)=$(boot)/dts
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archclean:
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$(Q)$(MAKE) $(clean)=$(boot)
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# Hacks to enable final link due to absence of link-time branch relexation
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# and gcc choosing optimal(shorter) branches at -O3
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#
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# vineetg Feb 2010: -mlong-calls switched off for overall kernel build
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# However lib/decompress_inflate.o (.init.text) calls
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# zlib_inflate_workspacesize (.text) causing relocation errors.
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# Thus forcing all exten calls in this file to be long calls
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export CFLAGS_decompress_inflate.o = -mmedium-calls
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export CFLAGS_initramfs.o = -mmedium-calls
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ifdef CONFIG_SMP
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export CFLAGS_core.o = -mmedium-calls
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endif
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