Nick Desaulniers 12051b318b mips: avoid explicit UB in assignment of mips_io_port_base ... The code in question is modifying a variable declared const through pointer manipulation. Such code is explicitly undefined behavior, and is the lone issue preventing malta_defconfig from booting when built with Clang: If an attempt is made to modify an object defined with a const-qualified type through use of an lvalue with non-const-qualified type, the behavior is undefined. LLVM is removing such assignments. A simple fix is to not declare variables const that you plan on modifying. Limiting the scope would be a better method of preventing unwanted writes to such a variable. Further, the code in question mentions "compiler bugs" without any links to bug reports, so it is difficult to know if the issue is resolved in GCC. The patch was authored in 2006, which would have been GCC 4.0.3 or 4.1.1. The minimal supported version of GCC in the Linux kernel is currently 4.6. For what its worth, there was UB before the commit in question, it just added a barrier and got lucky IRT codegen. I don't think there's any actual compiler bugs related, just runtime bugs due to UB. Link: https://github.com/ClangBuiltLinux/linux/issues/610 Fixes: 966f4406d9 ("[MIPS] Work around bad code generation for <asm/io.h>.") Reported-by: Nathan Chancellor <natechancellor@gmail.com> Debugged-by: Nathan Chancellor <natechancellor@gmail.com> Suggested-by: Eli Friedman <efriedma@quicinc.com> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> Tested-by: Nathan Chancellor <natechancellor@gmail.com> Signed-off-by: Paul Burton <paul.burton@mips.com> Cc: ralf@linux-mips.org Cc: jhogan@kernel.org Cc: Maciej W. Rozycki <macro@linux-mips.org> Cc: Hassan Naveed <hnaveed@wavecomp.com> Cc: Stephen Kitt <steve@sk2.org> Cc: Serge Semin <fancer.lancer@gmail.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Michal Hocko <mhocko@suse.com> Cc: linux-mips@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: clang-built-linux@googlegroups.com		2019-08-24 15:10:58 +01:00
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asm	mips: avoid explicit UB in assignment of mips_io_port_base	2019-08-24 15:10:58 +01:00
uapi/asm	Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next	2019-06-20 00:06:27 -04:00