Rework READ_ONCE() to improve codegen

Hi folks,

(trimmed CC list since v4 since this is largely just a rebase)

This is version five of the READ_ONCE() codegen improvement series that I've previously posted here:

RFC: https://lore.kernel.org/lkml/[email protected]
v2:  https://lore.kernel.org/lkml/[email protected]
v3:  https://lore.kernel.org/lkml/[email protected]
v4:  https://lore.kernel.org/lkml/[email protected]

The main change since v4 is that this is now based on top of the KCSAN changes queued in -tip (locking/kcsan) and therefore contains the patches necessary to avoid breaking sparc32 as well as some cleanups to consolidate {READ,WRITE}_ONCE() and data_race().

Other changes include:

* Treat 'char' as distinct from 'signed char' and 'unsigned char' for __builtin_types_compatible_p()

* Add a compile-time assertion that the argument to READ_ONCE_NOCHECK() points at something the same size as 'unsigned long'

I'm happy for all of this to go via -tip, or I can take it via arm64.

Please let me know.

Cheers,

Will

--->8

Will Deacon (18):
sparc32: mm: Fix argument checking in __srmmu_get_nocache()
sparc32: mm: Restructure sparc32 MMU page-table layout
sparc32: mm: Change pgtable_t type to pte_t * instead of struct page *
sparc32: mm: Reduce allocation size for PMD and PTE tables compiler/gcc: Raise minimum GCC version for kernel builds to 4.8
netfilter: Avoid assigning 'const' pointer to non-const pointer
net: tls: Avoid assigning 'const' pointer to non-const pointer
fault_inject: Don't rely on "return value" from WRITE_ONCE()
arm64: csum: Disable KASAN for do_csum()
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
gcov: Remove old GCC 3.4 support
kcsan: Rework data_race() so that it can be used by READ_ONCE()
READ_ONCE: Use data_race() to avoid KCSAN instrumentation linux/compiler.h: Remove redundant '#else'

 Documentation/process/changes.rst   |   2 +-
 arch/arm/crypto/Kconfig             |  12 +-
 arch/arm64/include/asm/barrier.h    |  16 +-
 arch/arm64/lib/csum.c               |  20 +-
 arch/sparc/include/asm/page_32.h    |  12 +-
 arch/sparc/include/asm/pgalloc_32.h |  11 +-
 arch/sparc/include/asm/pgtable_32.h |  40 +-
 arch/sparc/include/asm/pgtsrmmu.h   |  36 +-
 arch/sparc/include/asm/viking.h     |   5 +-
 arch/sparc/kernel/head_32.S         |   8 +-
 arch/sparc/mm/hypersparc.S          |   3 +-
 arch/sparc/mm/srmmu.c               |  95 ++---
 arch/sparc/mm/viking.S              |   5 +-
 crypto/Kconfig                      |   1 -
 drivers/xen/time.c                  |   2 +-
 include/asm-generic/barrier.h       |  16 +-
 include/linux/compiler-gcc.h        |   5 +-
 include/linux/compiler.h            | 207 +++++-----
 include/linux/compiler_types.h      |  26 ++
 init/Kconfig                        |   1 -
 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/tls/tls_main.c                  |   2 +-
 scripts/gcc-plugins/Kconfig         |   2 +-
 27 files changed, 257 insertions(+), 876 deletions(-)
 delete mode 100644 kernel/gcov/gcc_3_4.c

2.26.2.645.ge9eca65c58-goog