[PATCH v2 00/10] Rework READ_ONCE() to improve codegen

Will Deacon
2020-01-23T15:33:52Z

Hi folks,

This is version two of the patches I previously posted as an RFC here:

https://lore.kernel.org/lkml/20200110165636.28035-1-will@kernel.org

Changes since then include:

* Adopted a less vomit-inducing series of macros for __unqual_scalar_typeof

* Cast to 'const' in READ_ONCE() to prevent assignment to the resulting
expression

* Only warn once at build-time if GCC prior to 4.8 is detected...

* ... and then raise the minimum GCC version to 4.8, with an error for
older versions of the compiler

* Remove some dead gcov code so that the resulting diffstat can distract
from those less vomit-inducing macros I mentioned earlier on

Failing the build for older compilers is always a contentious topic, so
I've done that as a separate couple of patches on the end in case we end
up dropping or reverting them.

Cheers,

Will

Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>

--->8

Will Deacon (10):
compiler/gcc: Emit build-time warning for GCC prior to version 4.8
netfilter: Avoid assigning 'const' pointer to non-const pointer
fault_inject: Don't rely on "return value" from WRITE_ONCE()
READ_ONCE: Simplify implementations of {READ,WRITE}_ONCE()
READ_ONCE: Enforce atomicity for {READ,WRITE}_ONCE() memory accesses
READ_ONCE: Drop pointer qualifiers when reading from scalar types
locking/barriers: Use '__unqual_scalar_typeof' for load-acquire macros
arm64: barrier: Use '__unqual_scalar_typeof' for acquire/release
macros
compiler/gcc: Raise minimum GCC version for kernel builds to 4.8
gcov: Remove old GCC 3.4 support

Documentation/process/changes.rst | 2 +-
arch/arm/crypto/Kconfig | 12 +-
arch/arm64/include/asm/barrier.h | 16 +-
crypto/Kconfig | 1 -
drivers/xen/time.c | 2 +-
include/asm-generic/barrier.h | 16 +-
include/linux/compiler-gcc.h | 5 +-
include/linux/compiler.h | 129 +++----
include/linux/compiler_types.h | 21 ++
init/Kconfig | 5 +-
kernel/gcov/Kconfig | 24 --
kernel/gcov/Makefile | 3 +-
kernel/gcov/gcc_3_4.c | 573 ------------------------------
lib/fault-inject.c | 4 +-
net/netfilter/core.c | 2 +-
net/xdp/xsk_queue.h | 2 +-
scripts/Kconfig.include | 3 +
scripts/gcc-plugins/Kconfig | 4 +-
18 files changed, 111 insertions(+), 713 deletions(-)
delete mode 100644 kernel/gcov/gcc_3_4.c

--
2.25.0.341.g760bfbb309-goog