linux-kernel - Re: [PATCH -next] MIPS: VDSO: Fix build error with binutils 2.24 and earlier

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Message-ID: <20160105100630.GA26905@jhogan-linux.le.imgtec.org>
Date:	Tue, 5 Jan 2016 10:06:30 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Michal Marek <mmarek@...e.cz>
CC:	Guenter Roeck <linux@...ck-us.net>,
	Ralf Baechle <ralf@...ux-mips.org>,
	<linux-mips@...ux-mips.org>, <linux-kernel@...r.kernel.org>,
	Qais Yousef <qais.yousef@...tec.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH -next] MIPS: VDSO: Fix build error with binutils 2.24 and
 earlier

On Tue, Jan 05, 2016 at 10:20:59AM +0100, Michal Marek wrote:
> On 2015-12-24 13:57, James Hogan wrote:
> > On Thu, Dec 24, 2015 at 12:48:12PM +0000, James Hogan wrote:
> >> Hi Guenter,
> >>
> >> On Wed, Dec 23, 2015 at 09:04:31PM -0800, Guenter Roeck wrote:
> >>> Commit 2a037f310bab ("MIPS: VDSO: Fix build error") tries to fix a build
> >>> error seen with binutils 2.24 and earlier. However, the fix does not work,
> >>> and again results in the already known build errors if the kernel is built
> >>> with an earlier version of binutils.
> >>>
> >>> CC      arch/mips/vdso/gettimeofday.o
> >>> /tmp/ccnOVbHT.s: Assembler messages:
> >>> /tmp/ccnOVbHT.s:50: Error: can't resolve `_start' {*UND* section} - `L0 {.text section}
> >>> /tmp/ccnOVbHT.s:374: Error: can't resolve `_start' {*UND* section} - `L0 {.text section}
> >>> scripts/Makefile.build:258: recipe for target 'arch/mips/vdso/gettimeofday.o' failed
> >>> make[2]: *** [arch/mips/vdso/gettimeofday.o] Error 1
> >>>
> >>> Fixes: 2a037f310bab ("MIPS: VDSO: Fix build error")
> >>> Cc: Qais Yousef <qais.yousef@...tec.com>
> >>> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> >>> ---
> >>> Tested with binutils 2.25 and 2.22.
> >>>
> >>>  arch/mips/vdso/Makefile | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
> >>> index 018f8c7b94f2..14568900fc1d 100644
> >>> --- a/arch/mips/vdso/Makefile
> >>> +++ b/arch/mips/vdso/Makefile
> >>> @@ -26,7 +26,7 @@ aflags-vdso := $(ccflags-vdso) \
> >>>  # the comments on that file.
> >>>  #
> >>>  ifndef CONFIG_CPU_MIPSR6
> >>> -  ifeq ($(call ld-ifversion, -lt, 22500000, y),)
> >>> +  ifeq ($(call ld-ifversion, -lt, 22500000, y),y)
> >>
> >> I agree this is semantically correct, but there is something more evil
> >> going on here.
> >>
> >> Originally the check was version <= 2.24
> >> Qais' patch changed it to version >= 2.25 (intending version < 2.25)
> >> Your patch changes it to version < 2.25
> >>
> >> I think the reason this fixed the problem for Qais is actually that he
> >> probably had a similar toolchain version to what I'm using:
> >>
> >> GNU ld (Codescape GNU Tools 2015.06-05 for MIPS MTI Linux) 2.24.90
> >>
> >> ./scripts/ld-version.sh does this:
> >>
> >> print a[1]*10000000 + a[2]*100000 + a[3]*10000 + a[4]*100 + a[5];
> >>
> >> which changes that version number into:
> >>  20000000
> >> + 2400000
> >> +  900000 = 23300000
> >>
> >> I.e. it doesn't expect a[3] to be >= 10.
> >>
> >> Should we do something like this (increase multipliers on a[1] and
> >> a[2])?:
> >>
> >> diff --git a/scripts/ld-version.sh b/scripts/ld-version.sh
> >> index 198580d245e0..0b67edc5bc6f 100755
> >> --- a/scripts/ld-version.sh
> >> +++ b/scripts/ld-version.sh
> >> @@ -3,6 +3,6 @@
> >>  	{
> >>  	gsub(".*)", "");
> >>  	split($1,a, ".");
> >> -	print a[1]*10000000 + a[2]*100000 + a[3]*10000 + a[4]*100 + a[5];
> >> +	print a[1]*100000000 + a[2]*1000000 + a[3]*10000 + a[4]*100 + a[5];
> >>  	exit
> >>  	}
> >>
> >> which gives 2.24.90 => 224900000.
> >>
> >> All call sites would need updating too to add the extra 0, but a quick
> >> git grep isn't showing any other ones than this one.
> > 
> > Actually, linux-next includes this commit which uses ld-ifversion too:
> > 
> > 19a3cc83353e3bb4bc28769f8606139a3d350d2d
> > "Kbuild, lto: Add Link Time Optimization support v3"
> 
> That commit needs updating for other reasons, so feel free to fix
> ld-ifversion and its usage in arch/mips.

Thanks. This change is now in linux-next, and will hopefully be included
in v4.4:
http://patchwork.linux-mips.org/patch/11931/

Cheers
James

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