linux-kernel - Re: [PATCH] kbuild: Disallow GCC 4.1.0 / 4.1.1

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Message-Id: <200901021443.58769.bzolnier@gmail.com>
Date:	Fri, 2 Jan 2009 14:43:58 +0100
From:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	David Miller <davem@...emloft.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	akpm@...ux-foundation.org, rdreier@...co.com,
	ian.campbell@...rix.com, jeremy.fitzhardinge@...rix.com,
	deller@....de, rusty@...tcorp.com.au, linux-parisc@...r.kernel.org,
	linux-kernel@...r.kernel.org, kyle@...artin.ca, randolph@...sq.org,
	sam@...nborg.org, dave@...uly1.hia.nrc.ca
Subject: Re: [PATCH] kbuild: Disallow GCC 4.1.0 / 4.1.1

On Friday 02 January 2009, Ingo Molnar wrote:
> 
> * David Miller <davem@...emloft.net> wrote:
> 
> > From: Linus Torvalds <torvalds@...ux-foundation.org>
> > Date: Wed, 31 Dec 2008 13:22:53 -0800 (PST)
> > 
> > > On Wed, 31 Dec 2008, Andrew Morton wrote:
> > > > 
> > > > Adrian claimed that it was gcc-4.1.0 and 4.1.1 only.  He proposed
> > > > banning them: http://lkml.org/lkml/2008/8/5/444
> > > 
> > > If it really is just those releases, then yes, considering the number 
> > > of cases we apparently have, and considering how ugly it is in some 
> > > cases to move the weak function anywhere else, maybe banning those 
> > > versions is the proper thing to do.
> > > 
> > > It probably won't hurt very many people - yeah, some people will be 
> > > forced to upgrade, but I have this memory of early 4.1 having had 
> > > other bugs anyway, so it's probably a good idea.
> > 
> > I think this is probably the best way to handle this.
> 
> okay - to move this matter from the discussion-space to the 
> solution-space, how about the patch below? (tested on x86 with a 
> non-affected compiler version.)

...or we can just merge Adrian's patch from June 2008 which also fixes
the issue nicely.

OTOH your patch has an advantage of addressing the problem in the more
appropriate place (include/linux/compiler.h) and from what I see allows
us to remove previous gcc 4.1.0 check from init/main.c?

> 	Ingo
> 
> -------------->
> From e6346e5ab54dcf12888a79dfd5402f5de09b3fad Mon Sep 17 00:00:00 2001
> From: Ingo Molnar <mingo@...e.hu>
> Date: Fri, 2 Jan 2009 12:46:22 +0100
> Subject: [PATCH] kbuild: Disallow GCC 4.1.0 / 4.1.1
> 
> Impact: fix crashes that can trigger if built with GCC 4.1.0 or 4.1.1
> 
> GCC 4.1.0 and 4.1.1 has a bug that can miscompile __weak symbols,
> by inlining __weak functions into same-file call sites - breaking the
> kernel if the __weak symbol is overriden later on.
> 
> In the past we tried to work around this problem by artificially
> isolating call site and definition site - but these bugs tend to
> pop up regularly:
> 
>  43a2563: sparseirq: move __weak symbols into separate compilation unit
>  13a0c3c: sparseirq: work around compiler optimizing away __weak functions
> 
> And Linus has extended Sparse to report same-file callsites for __weak
> symbols - which gave two dozen hits.
> 
> We have not found a clean way to work around this bug on the source
> code level (noinline and explicit barrier()s are ignored by GCC), so we do
> not allow these compilers (which are quite rare these days, have other bugs
> and are superceded by the 4.1.2 bugfix release anyway).
> 
> Kernel builds under gcc 410 or 411 will now fail with this error message:
> 
>   Sorry, your compiler is too old, too buggy or not recognized.
> 
> Signed-off-by: Ingo Molnar <mingo@...e.hu>
> ---
>  include/linux/compiler.h |   17 +++++++++++++++--
>  1 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index ea7c6be..dd558ce 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -36,12 +36,25 @@ extern void __chk_io_ptr(const volatile void __iomem *);
>  
>  #ifdef __KERNEL__
>  
> -#if __GNUC__ >= 4
> +/*
> + * GCC 4.1.0 and 4.1.1 has a bug that can miscompile __weak symbols,
> + * by inlining __weak functions into same-file call sites - breaking the
> + * kernel if the __weak symbol is overriden later on.
> + *
> + * We have not found a clean way to work around this bug on the source
> + * code level, so we do not allow these compilers (which are quite
> + * rare these days, have other bugs and are superceded by the 4.1.2
> + * bugfix release anyway):
> + */
> +#define gcc41_inlining_bug \
> +	(__GNUC__ == 4 && __GNUC_MINOR__ == 1 && __GNUC_PATCHLEVEL__ <= 1)
> +
> +#if __GNUC__ >= 4 && !gcc41_inlining_bug
>  # include <linux/compiler-gcc4.h>
>  #elif __GNUC__ == 3 && __GNUC_MINOR__ >= 2
>  # include <linux/compiler-gcc3.h>
>  #else
> -# error Sorry, your compiler is too old/not recognized.
> +# error Sorry, your compiler is too old, too buggy or not recognized.
>  #endif
>  
>  #define notrace __attribute__((no_instrument_function))
--
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