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

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Message-ID: <20151224124812.GA5376@jhogan-linux.le.imgtec.org>
Date:	Thu, 24 Dec 2015 12:48:12 +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>
Subject: Re: [PATCH -next] MIPS: VDSO: Fix build error with binutils 2.24 and
 earlier

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.

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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