3f135e57a4
The GCC '-maccumulate-outgoing-args' flag is enabled for most configs,
mostly because of issues which are no longer relevant. For most
configs, and with most recent versions of GCC, it's no longer needed.
Clarify which cases need it, and only enable it for those cases. Also
produce a compile-time error for the ftrace graph + mcount + '-Os' case,
which will otherwise cause runtime failures.
The main benefit of '-maccumulate-outgoing-args' is that it prevents an
ugly prologue for functions which have aligned stacks. But removing the
option also has some benefits: more readable argument saves, smaller
text size, and (presumably) slightly improved performance.
Here are the object size savings for 32-bit and 64-bit defconfig
kernels:
text data bss dec hex filename
10006710 3543328 1773568 15323606 e9d1d6 vmlinux.x86-32.before
9706358 3547424 1773568 15027350 e54c96 vmlinux.x86-32.after
text data bss dec hex filename
10652105 4537576 843776 16033457 f4a6b1 vmlinux.x86-64.before
10639629 4537576 843776 16020981 f475f5 vmlinux.x86-64.after
That comes out to a 3% text size improvement on x86-32 and a 0.1% text
size improvement on x86-64.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170316193133.zrj6gug53766m6nn@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>
53 lines
2.5 KiB
Plaintext
53 lines
2.5 KiB
Plaintext
# CPU tuning section - shared with UML.
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# Must change only cflags-y (or [yn]), not CFLAGS! That makes a difference for UML.
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#-mtune exists since gcc 3.4
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HAS_MTUNE := $(call cc-option-yn, -mtune=i386)
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ifeq ($(HAS_MTUNE),y)
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tune = $(call cc-option,-mtune=$(1),$(2))
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else
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tune = $(call cc-option,-mcpu=$(1),$(2))
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endif
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align := $(cc-option-align)
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cflags-$(CONFIG_M486) += -march=i486
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cflags-$(CONFIG_M586) += -march=i586
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cflags-$(CONFIG_M586TSC) += -march=i586
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cflags-$(CONFIG_M586MMX) += -march=pentium-mmx
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cflags-$(CONFIG_M686) += -march=i686
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cflags-$(CONFIG_MPENTIUMII) += -march=i686 $(call tune,pentium2)
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cflags-$(CONFIG_MPENTIUMIII) += -march=i686 $(call tune,pentium3)
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cflags-$(CONFIG_MPENTIUMM) += -march=i686 $(call tune,pentium3)
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cflags-$(CONFIG_MPENTIUM4) += -march=i686 $(call tune,pentium4)
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cflags-$(CONFIG_MK6) += -march=k6
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# Please note, that patches that add -march=athlon-xp and friends are pointless.
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# They make zero difference whatsosever to performance at this time.
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cflags-$(CONFIG_MK7) += -march=athlon
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cflags-$(CONFIG_MK8) += $(call cc-option,-march=k8,-march=athlon)
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cflags-$(CONFIG_MCRUSOE) += -march=i686 $(align)-functions=0 $(align)-jumps=0 $(align)-loops=0
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cflags-$(CONFIG_MEFFICEON) += -march=i686 $(call tune,pentium3) $(align)-functions=0 $(align)-jumps=0 $(align)-loops=0
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cflags-$(CONFIG_MWINCHIPC6) += $(call cc-option,-march=winchip-c6,-march=i586)
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cflags-$(CONFIG_MWINCHIP3D) += $(call cc-option,-march=winchip2,-march=i586)
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cflags-$(CONFIG_MCYRIXIII) += $(call cc-option,-march=c3,-march=i486) $(align)-functions=0 $(align)-jumps=0 $(align)-loops=0
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cflags-$(CONFIG_MVIAC3_2) += $(call cc-option,-march=c3-2,-march=i686)
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cflags-$(CONFIG_MVIAC7) += -march=i686
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cflags-$(CONFIG_MCORE2) += -march=i686 $(call tune,core2)
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cflags-$(CONFIG_MATOM) += $(call cc-option,-march=atom,$(call cc-option,-march=core2,-march=i686)) \
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$(call cc-option,-mtune=atom,$(call cc-option,-mtune=generic))
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# AMD Elan support
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cflags-$(CONFIG_MELAN) += -march=i486
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# Geode GX1 support
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cflags-$(CONFIG_MGEODEGX1) += -march=pentium-mmx
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cflags-$(CONFIG_MGEODE_LX) += $(call cc-option,-march=geode,-march=pentium-mmx)
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# add at the end to overwrite eventual tuning options from earlier
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# cpu entries
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cflags-$(CONFIG_X86_GENERIC) += $(call tune,generic,$(call tune,i686))
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# Bug fix for binutils: this option is required in order to keep
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# binutils from generating NOPL instructions against our will.
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ifneq ($(CONFIG_X86_P6_NOP),y)
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cflags-y += $(call cc-option,-Wa$(comma)-mtune=generic32,)
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endif
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