|author||Paul Burton <firstname.lastname@example.org>||2018-08-20 15:36:17 -0700|
|committer||Paul Burton <email@example.com>||2018-08-21 10:05:45 -0700|
|parent||MIPS: Avoid move psuedo-instruction whilst using MIPS_ISA_LEVEL (diff)|
compiler.h: Allow arch-specific asm/compiler.h
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 . 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.  https://lists.01.org/pipermail/kbuild-all/2018-August/051175.html Signed-off-by: Paul Burton <firstname.lastname@example.org> Reviewed-by: Masahiro Yamada <email@example.com> Patchwork: https://patchwork.linux-mips.org/patch/20269/ Cc: Arnd Bergmann <firstname.lastname@example.org> Cc: James Hogan <email@example.com> Cc: Masahiro Yamada <firstname.lastname@example.org> Cc: Ralf Baechle <email@example.com> Cc: firstname.lastname@example.org Cc: email@example.com Cc: firstname.lastname@example.org
Diffstat (limited to 'arch/Kconfig')
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig
index 1aa59063f1fd..5c7c48e7b727 100644
@@ -971,4 +971,12 @@ config REFCOUNT_FULL
against various use-after-free conditions that can be used in
security flaw exploits.
+ 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.