[PATCH] ARM: Blacklist GCC 4.8.0 to GCC 4.8.2 - PR58854

[David Laight]

From: Russell King
> These stock GCC versions miscompile the kernel by incorrectly optimising
> the function epilogue code - by first increasing the stack pointer, and
> then loading entries from below the stack.  This means that an opportune
> interrupt or exception will corrupt the current function's saved state,
> which may result in the parent function seeing different register
> values.
> 
> As this bug has been known to result in corrupted filesystems, and these
> buggy compiler versions seem to be frequently used, we have little
> option but to blacklist these compiler versions.
> 
> Distributions may have fixed PR58854, but as their compilers are totally
> indistinguishable from the buggy versions, it is unfortunate that this
> also results in those also being blacklisted.  Given the filesystem
> corruption potential of the original, this is the lesser evil.  People
> who want to build with their fixed compiler versions will need to adjust
> the kernel source.  (Distros need to think about the implications of
> fixing such a compiler bug, and consider how to ensure that their fixed
> compiler versions can be detected if they wish to avoid this.)
> 
> Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> ---
> 
> This is what I came up with - this places the build check right at the
> beginning of the kernel build, rather than at some point where
> linux/compiler.h gets included.  Note that this is where we have
> previous ARM specific GCC version blacklisting.  I'm blacklisting
> GCC 4.8.0 to GCC 4.8.2 inclussive, which seems to be the right versions
> for stock GCC.
> 
> I was in two minds whether to include 4.8.3 as Linaro released a buggy
> toolchain which identifies itself as 4.8.3, but I decided that's also
> a distro problem.  IMHO Linaro should really think about taking that
> compiler down given the seriousness of this bug and it being
> indistinguishable from the fixed stock version.
> 
>  arch/arm/kernel/asm-offsets.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c
> index 713e807621d2..e14c1a12b414 100644
> --- a/arch/arm/kernel/asm-offsets.c
> +++ b/arch/arm/kernel/asm-offsets.c
> @@ -10,6 +10,7 @@
>   * it under the terms of the GNU General Public License version 2 as
>   * published by the Free Software Foundation.
>   */
> +#include <linux/compiler.h>
>  #include <linux/sched.h>
>  #include <linux/mm.h>
>  #include <linux/dma-mapping.h>
> @@ -39,10 +40,19 @@
>   * GCC 3.2.x: miscompiles NEW_AUX_ENT in fs/binfmt_elf.c
>   *            (http://gcc.gnu.org/PR8896) and incorrect structure
>   *	      initialisation in fs/jffs2/erase.c
> + * GCC 4.8.0-4.8.2: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58854
> + *	      miscompiles find_get_entry(), and can result in EXT3 and EXT4
> + *	      filesystem corruption (possibly other FS too).
>   */
> +#ifdef __GNUC__
>  #if (__GNUC__ == 3 && __GNUC_MINOR__ < 3)
>  #error Your compiler is too buggy; it is known to miscompile kernels.
> -#error    Known good compilers: 3.3
> +#error    Known good compilers: 3.3, 4.x

Except that isn't true since 4.8.0 isn't a good compiler.

> +#endif
> +#if GCC_VERSION >= 40800 || GCC_VERSION < 40803
> +#error Your compiler is too buggy; it is known to miscompile kernels
> +#error and result in filesystem corruption and oopses.
> +#endif
>  #endif

You are mixing the style of the version check.
Why not the single test:
#if GCC_VERSION < 30300 || (GCC_VERSION >= 40800 && GCC_VERSION < 40803)
#error Your compiler is too buggy; it is known to miscompile code.
#error Known good compilers: 3.3 onwards excluding 4.8.0 through 4.8.2
#endif

	David

> 
>  int main(void)
> --
> 1.8.3.1