linux-kernel - Re: [PATCH 2/2] Add CONFIG_READABLE

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Date:	Sat, 12 May 2012 22:23:40 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	Andi Kleen <ak@...ux.intel.com>, Andi Kleen <andi@...stfloor.org>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH 2/2] Add CONFIG_READABLE_ASM

On Tue, May 8, 2012 at 9:36 PM, Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
> On Thu, Apr 12, 2012 at 10:35 PM, Sam Ravnborg <sam@...nborg.org> wrote:
>> On Thu, Apr 12, 2012 at 10:17:07PM +0200, Geert Uytterhoeven wrote:
>>> On Thu, Apr 12, 2012 at 22:07, Sam Ravnborg <sam@...nborg.org> wrote:
>>> > Could you try this:
>>> >
>>> > cc-disable-opt = $(call try-run,\
>>> >        $(CC) $(KBUILD_CPPFLAGS) $(KBUILD_CFLAGS) -f$(strip $(1)) -c -xc /dev/null -o "$TMP",-fno-$(strip $(1)))
>>> >
>>> > KBUILD_CFLAGS += $(call cc-disable-opt, ipa-cp-clone)
>>> >
>>> >
>>> > It will try if "gcc -fipa-cp-clone" is supported,
>>> > and add -fno-ipa-cp-clone in that case.
>>>
>>> Unfortunately not:
>>>
>>> m68k-linux-gnu-gcc -Wp,-MD,kernel/.bounds.s.d  -nostdinc -isystem
>>> /usr/lib/gcc/m68k-linux-gnu/4.1.2/include
>>> -I/scratch/geert/linux/linux-next/arch/m68k/include
>>> Iarch/m68k/include/generated -Iinclude  -include
>>> /scratch/geert/linux/linux-next/include/linux/kconfig.h -D__KERNEL__
>>> -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing
>>> -fno-common -Werror-implicit-function-declaration -Wno-format-security
>>> -fno-delete-null-pointer-checks -Os -fno-reorder-blocks
>>> -fno-ipa-cp-clone -pipe -fno-strength-reduce -ffixed-a2
>>> -fno-omit-frame-pointer -fno-optimize-sibling-calls -g
>>> -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(bounds)"
>>> -D"KBUILD_MODNAME=KBUILD_STR(bounds)" -fverbose-asm -S -o
>>> kernel/bounds.s kernel/bounds.c
>>> cc1: error: unrecognized command line option "-fno-ipa-cp-clone"
>>> make[1]: *** [kernel/bounds.s] Error 1
>>> make: *** [prepare0] Error 2
>>
>> So with the above command-line gcc fails with an exit code for -fno-ipa-cp-clone.
>> But with cc-option it does not.
>>
>> Can you dig out the command-line used for cc-option?
>> We may be able to analyze why it fails in the above case, but
>> not with cc-option.
>
> gcc -D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs
> -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration
> -Wno-format-security -fno-delete-null-pointer-checks -Os
> -fno-ipa-cp-clone -c -xc /dev/null -o .6376.tmp
>
> So it's running "gcc" instead of "m68k-linux-gnu-gcc".

Found it using the patch below to log all try-run invocations:

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 6a3ee98..12eb839 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -88,6 +88,7 @@ TMPOUT := $(if $(KBUILD_EXTMOD),$(firstword
$(KBUILD_EXTMOD))/)
 try-run = $(shell set -e;              \
        TMP="$(TMPOUT).$$$$.tmp";       \
        TMPO="$(TMPOUT).$$$$.o";        \
+       echo "$(1)" >> /tmp/x;          \
        if ($(1)) >/dev/null 2>&1;      \
        then echo "$(2)";               \
        else echo "$(3)";               \

| --- a/Makefile
| +++ b/Makefile
| @@ -564,6 +564,16 @@ else
|  KBUILD_CFLAGS  += -O2
|  endif
|
| +ifdef CONFIG_READABLE_ASM
| +# Disable optimizations that make assembler listings hard to read.
| +# reorder blocks reorders the control in the function
| +# ipa clone creates specialized cloned functions
| +# partial inlining inlines only parts of functions
| +KBUILD_CFLAGS += $(call cc-option,-fno-reorder-blocks,) \
| +                 $(call cc-option,-fno-ipa-cp-clone,) \
| +                 $(call cc-option,-fno-partial-inlining)
| +endif
| +

The above calls cc-option using CC = gcc, as my cross compiler
is only setup in the next line:

| include $(srctree)/arch/$(SRCARCH)/Makefile

This affects all architectures that setup CROSS_COMPILE in their arch/*/Makefile
(blackfin, h8300, m68k, mips, parisc, score, sh, tile, unicore32, xtensa).

Worse, m68k, sh, and xtensa call cc-option in their arch/*/Makefile
before CROSS_COMPILE is setup, causing those checks to be done against
the host compiler when cross-compiling.

Sending out patches, as soon as the (automatic) "git gc" completes...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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