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

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Date:	Thu, 24 Dec 2015 12:57:26 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	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>, Michal Marek <mmarek@...e.cz>
Subject: Re: [PATCH -next] MIPS: VDSO: Fix build error with binutils 2.24 and
 earlier

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"

Cheers
James

> 
> Cheers
> James
> 
> >      $(warning MIPS VDSO requires binutils >= 2.25)
> >      obj-vdso-y := $(filter-out gettimeofday.o, $(obj-vdso-y))
> >      ccflags-vdso += -DDISABLE_MIPS_VDSO
> > -- 
> > 2.1.4
> > 
> > 



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