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

[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
+#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
 
 int main(void)
-- 
1.8.3.1