linux-kernel - [PATCH 00/10] raise minimum GCC version to 5.1

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Date:   Fri, 10 Sep 2021 16:40:37 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Nathan Chancellor <nathan@...nel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 00/10] raise minimum GCC version to 5.1

commit fad7cd3310db ("nbd: add the check to prevent overflow in
__nbd_ioctl()")

raised an issue from the fallback helpers added in

commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and add fallback code")

Specifically, the helpers for checking whether the results of a
multiplication overflowed (__unsigned_mul_overflow,
__signed_add_overflow) use the division operator when
!COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW. This is problematic for 64b
operands on 32b hosts.

Also, because the macro is type agnostic, it is very difficult to write
a similarly type generic macro that dispatches to one of:
* div64_s64
* div64_u64
* div_s64
* div_u64

Raising the minimum supported versions allows us to remove all of the
fallback helpers for !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW, instead
dispatching the compiler builtins.

arm64 has already raised the minimum supported GCC version to 5.1, do
this for all targets now. See the link below for the previous
discussion.

Additional patches cleaning up a few obsolete version checks.

Link: https://lore.kernel.org/all/20210909182525.372ee687@canb.auug.org.au/
Link: https://lore.kernel.org/lkml/CAK7LNASs6dvU6D3jL2GG3jW58fXfaj6VNOe55NJnTB8UPuk2pA@mail.gmail.com/
Link: https://github.com/ClangBuiltLinux/linux/issues/1438

Nick Desaulniers (10):
  Documentation: raise minimum supported version of GCC to 5.1
  compiler.h: drop fallback overflow checkers
  mm/ksm: remove old GCC 4.9+ check
  Kconfig.debug: drop GCC 5+ version check for DWARF5
  riscv: remove Kconfig check for GCC version for ARCH_RV64I
  powerpc: remove GCC version check for UPD_CONSTR
  arm64: remove GCC version check for ARCH_SUPPORTS_INT128
  Makefile: drop GCC < 5 -fno-var-tracking-assignments workaround
  compiler-gcc.h: drop checks for older GCC versions
  vmlinux.lds.h: remove old check for GCC 4.9

 Documentation/process/changes.rst    |   2 +-
 Makefile                             |   6 --
 arch/arm64/Kconfig                   |   2 +-
 arch/powerpc/include/asm/asm-const.h |  10 --
 arch/riscv/Kconfig                   |   2 +-
 include/asm-generic/vmlinux.lds.h    |   4 -
 include/linux/compiler-clang.h       |  13 ---
 include/linux/compiler-gcc.h         |   8 +-
 include/linux/overflow.h             | 138 +-------------------------
 lib/Kconfig.debug                    |   2 +-
 mm/ksm.c                             |   2 -
 scripts/min-tool-version.sh          |   8 +-
 tools/include/linux/compiler-gcc.h   |   8 +-
 tools/include/linux/overflow.h       | 140 +--------------------------
 14 files changed, 13 insertions(+), 332 deletions(-)


base-commit: 2d338201d5311bcd79d42f66df4cecbcbc5f4f2c
-- 
2.33.0.309.g3052b89438-goog