Re: missing .data.shared_align placement in vmlinux

[Jeremy Fitzhardinge]

 On 08/04/2010 01:40 PM, Sam Ravnborg wrote:
> [Resend - this time with Jeremy included in To: ]
>
> Jeremy - you introduced this in ("x86/i386: Put aligned
> stack-canary in percpu shared_aligned section")
> 53f824520b6d84ca5b4a8fd71addc91dbf64357e
>
> Does the following simple fix look correct to you?
> [See below]
>
> 	Sam
>
> On Wed, Aug 04, 2010 at 10:28:06PM +0200, Sam Ravnborg wrote:
> > On Wed, Aug 04, 2010 at 02:12:03PM -0400, Mike Frysinger wrote:
> > > On Wed, Aug 4, 2010 at 07:56, Sam Ravnborg wrote:
> > > > On Fri, May 21, 2010 at 04:58:53PM -0400, Mike Frysinger wrote:
> > > > > am i missing something or does the .data.shared_align section lack
> > > > > definition in vmlinux.lds.h and all arch vmlinux.lds.S files ?
> > > > >
> > > > > with the recent change "net: remove time limit in process_backlog()",
> > > > > the softnet_data variable changed from "DEFINE_PER_CPU()" to
> > > > > "DEFINE_PER_CPU_ALIGNED()" which moved it from the .data section to
> > > > > the .data.shared_align section.  i'm not saying this patch is wrong,
> > > > > just that is what caused me to notice this larger problem.  no one
> > > > > else in the kernel is using this aligned macro variant, so i imagine
> > > > > that's why no one has noticed yet.

That's a bit odd and embarrassing...  I guess the stack_canary stuff is 
only visible when using CONFIG_CC_STACKPROTECTOR.

> > > > > since .data.shared_align isnt declared in any vmlinux files that i can
> > > > > see, the linker just places it last.  this "just works" for most
> > > > > people, but when building a ROM kernel on Blackfin systems, it causes
> > > > > section overlap errors:
> > > > > bfin-uclinux-ld.real: section .init.data [00000000202e06b8 ->
> > > > > 00000000202e48b7] overlaps section .data.shared_aligned
> > > > > [00000000202e06b8 ->  00000000202e0723]
> > > > > i imagine other arches which support the ROM config option and thus do
> > > > > funky placement would see similar issues ...
> > > > >
> > > > > on x86, it is stuck in a dedicated section:
> > > > >    [ 8] .data             PROGBITS        ffffffff810ec000 2ec000
> > > > > 0303a8 00  WA  0   0 4096
> > > > >    [ 9] .data.shared_alig PROGBITS        ffffffff8111c3c0 31c3c0
> > > > > 0000c8 00  WA  0   0 64
> > > > >
> > > > > the ifdef forest in asm-generic/percpu.h is beyond a quick glance&
> > > > > fix, so i leave it up to someone else ;)
> > > > as there any resolution on this?
> > > > I briefly looked at it some time ago.
> > > > And it looks like a plain oversight.
> > > no, it's still broken in 2.6.35 :(
> > > $ make ARCH=blackfin BF537-STAMP_defconfig
> > > $ make ARCH=blackfin -s -j4
> > > $ readelf -WS vmlinux | grep '\<data\>'
> > >    [10] .data             PROGBITS        0018369c 17269c 012964 00  WA  0   0  4
> > >    [11] .data..shared_aligned PROGBITS        00196000 185000 00006c 00
> > >   WA  0   0  4
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index 030a954..e87260f 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -150,6 +150,7 @@
>   #define DATA_DATA							\
>   	*(.data)							\
>   	*(.ref.data)							\
> +	*(.data..shared_aligned) /* percpu related */			\

Typo?  Shouldn't that be ".data.shared_aligned"?  Or where does the '..' 
come from?

    J
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/