4.18-stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 04f264d3a8b0eb25d378127bd78c3c9a0261c828 ]
We have a need to override the definition of barrier_before_unreachable() for MIPS, which means we either need to add architecture-specific code into linux/compiler-gcc.h or we need to allow the architecture to provide a header that can define the macro before the generic definition. The latter seems like the better approach.
A straightforward approach to the per-arch header is to make use of asm-generic to provide a default empty header & adjust architectures which don't need anything specific to make use of that by adding the header to generic-y. Unfortunately this doesn't work so well due to commit 28128c61e08e ("kconfig.h: Include compiler types to avoid missed struct attributes") which caused linux/compiler_types.h to be included in the compilation of every C file via the -include linux/kconfig.h flag in c_flags.
Because the -include flag is present for all C files we compile, we need the architecture-provided header to be present before any C files are compiled. If any C files can be compiled prior to the asm-generic header wrappers being generated then we hit a build failure due to missing header. Such cases do exist - one pointed out by the kbuild test robot is the compilation of arch/ia64/kernel/nr-irqs.c, which occurs as part of the archprepare target [1].
This leaves us with a few options:
1) Use generic-y & fix any build failures we find by enforcing ordering such that the asm-generic target occurs before any C compilation, such that linux/compiler_types.h can always include the generated asm-generic wrapper which in turn includes the empty asm-generic header. This would rely on us finding all the problematic cases - I don't know for sure that the ia64 issue is the only one.
2) Add an actual empty header to each architecture, so that we don't need the generated asm-generic wrapper. This seems messy.
3) Give up & add #ifdef CONFIG_MIPS or similar to linux/compiler_types.h. This seems messy too.
4) Include the arch header only when it's actually needed, removing the need for the asm-generic wrapper for all other architectures.
This patch allows us to use approach 4, by including an asm/compiler.h header from linux/compiler_types.h after the inclusion of the compiler-specific linux/compiler-*.h header(s). We do this conditionally, only when CONFIG_HAVE_ARCH_COMPILER_H is selected, in order to avoid the need for asm-generic wrappers & the associated build ordering issue described above. The asm/compiler.h header is included after the generic linux/compiler-*.h header(s) for consistency with the way linux/compiler-intel.h & linux/compiler-clang.h are included after the linux/compiler-gcc.h header that they override.
[1] https://lists.01.org/pipermail/kbuild-all/2018-August/051175.html
Signed-off-by: Paul Burton paul.burton@mips.com Reviewed-by: Masahiro Yamada yamada.masahiro@socionext.com Patchwork: https://patchwork.linux-mips.org/patch/20269/ Cc: Arnd Bergmann arnd@arndb.de Cc: James Hogan jhogan@kernel.org Cc: Masahiro Yamada yamada.masahiro@socionext.com Cc: Ralf Baechle ralf@linux-mips.org Cc: linux-arch@vger.kernel.org Cc: linux-kbuild@vger.kernel.org Cc: linux-mips@linux-mips.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/Kconfig | 8 ++++++++ include/linux/compiler_types.h | 12 ++++++++++++ 2 files changed, 20 insertions(+)
diff --git a/arch/Kconfig b/arch/Kconfig index f03b72644902..a18371a36e03 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -977,4 +977,12 @@ config REFCOUNT_FULL against various use-after-free conditions that can be used in security flaw exploits.
+config HAVE_ARCH_COMPILER_H + bool + help + An architecture can select this if it provides an + asm/compiler.h header that should be included after + linux/compiler-*.h in order to override macro definitions that those + headers generally provide. + source "kernel/gcov/Kconfig" diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index a8ba6b04152c..55e4be8b016b 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -78,6 +78,18 @@ extern void __chk_io_ptr(const volatile void __iomem *); #include <linux/compiler-clang.h> #endif
+/* + * Some architectures need to provide custom definitions of macros provided + * by linux/compiler-*.h, and can do so using asm/compiler.h. We include that + * conditionally rather than using an asm-generic wrapper in order to avoid + * build failures if any C compilation, which will include this file via an + * -include argument in c_flags, occurs prior to the asm-generic wrappers being + * generated. + */ +#ifdef CONFIG_HAVE_ARCH_COMPILER_H +#include <asm/compiler.h> +#endif + /* * Generic compiler-dependent macros required for kernel * build go below this comment. Actual compiler/compiler version