[PATCH 00/11] Bump the minimum supported version of LLVM to 13.0.1

[PATCH 00/11] Bump the minimum supported version of LLVM to 13.0.1

[Nathan Chancellor]

Hi all,

This series bumps the minimum supported version of LLVM for building the
kernel to 13.0.1. The first patch does the bump and all subsequent
patches clean up all the various workarounds and checks for earlier
versions.

Quoting the first patch's commit message for those that were only on CC
for the clean ups:

  When __builtin_mul_overflow() has arguments that differ in terms of
  signedness and width, LLVM may generate a libcall to __muloti4 because
  it performs the checks in terms of 65-bit multiplication. This issue
  becomes harder to hit (but still possible) after LLVM 12.0.0, which
  includes a special case for matching widths but different signs.

  To gain access to this special case, which the kernel can take advantage
  of when calls to __muloti4 appear, bump the minimum supported version of
  LLVM for building the kernel to 13.0.1. 13.0.1 was chosen because there
  is minimal impact to distribution support while allowing a few more
  workarounds to be dropped in the kernel source than if 12.0.0 were
  chosen. Looking at container images of up to date distribution versions:

    archlinux:latest              clang version 16.0.6
    debian:oldoldstable-slim      clang version 7.0.1-8+deb10u2 (tags/RELEASE_701/final)
    debian:oldstable-slim         Debian clang version 11.0.1-2
    debian:stable-slim            Debian clang version 14.0.6
    debian:testing-slim           Debian clang version 16.0.6 (19)
    debian:unstable-slim          Debian clang version 16.0.6 (19)
    fedora:38                     clang version 16.0.6 (Fedora 16.0.6-3.fc38)
    fedora:latest                 clang version 17.0.6 (Fedora 17.0.6-1.fc39)
    fedora:rawhide                clang version 17.0.6 (Fedora 17.0.6-1.fc40)
    opensuse/leap:latest          clang version 15.0.7
    opensuse/tumbleweed:latest    clang version 17.0.6
    ubuntu:focal                  clang version 10.0.0-4ubuntu1
    ubuntu:latest                 Ubuntu clang version 14.0.0-1ubuntu1.1
    ubuntu:rolling                Ubuntu clang version 16.0.6 (15)
    ubuntu:devel                  Ubuntu clang version 17.0.6 (3)

  The only distribution that gets left behind is Debian Bullseye, as the
  default version is 11.0.1; other distributions either have a newer
  version than 13.0.1 or one older than the current minimum of 11.0.0.
  Debian has easy access to more recent LLVM versions through
  apt.llvm.org, so this is not as much of a concern. There are also the
  kernel.org LLVM toolchains, which should work with distributions with
  glibc 2.28 and newer.

  Another benefit of slimming up the number of supported versions of LLVM
  for building the kernel is reducing the build capacity needed to support
  a matrix that builds with each supported version, which allows a matrix
  to reallocate the freed up build capacity towards something else, such
  as more configuration combinations.

This passes my build matrix with all supported versions.

This is based on Andrew's mm-nonmm-unstable to avoid trivial conflicts
with my series to update the LLVM links across the repository [1] but I
can easily rebase it to linux-kbuild if Masahiro would rather these
patches go through there (and defer the conflict resolution to the merge
window).

[1]: https://lore.kernel.org/20240109-update-llvm-links-v1-0-eb09b59db071@kernel.org/

---
Nathan Chancellor (11):
      kbuild: Raise the minimum supported version of LLVM to 13.0.1
      Makefile: Drop warn-stack-size plugin opt
      x86: Drop stack-alignment plugin opt
      ARM: Remove Thumb2 __builtin_thread_pointer workaround for Clang
      arm64: Kconfig: Clean up tautological LLVM version checks
      powerpc: Kconfig: Remove tautology in CONFIG_COMPAT
      riscv: Remove MCOUNT_NAME workaround
      riscv: Kconfig: Remove version dependency from CONFIG_CLANG_SUPPORTS_DYNAMIC_FTRACE
      fortify: Drop Clang version check for 12.0.1 or newer
      lib/Kconfig.debug: Update Clang version check in CONFIG_KCOV
      compiler-clang.h: Update __diag_clang() macros for minimum version bump

 Documentation/process/changes.rst |  2 +-
 Makefile                          |  8 --------
 arch/arm/include/asm/current.h    |  8 +-------
 arch/arm64/Kconfig                |  5 +----
 arch/powerpc/Kconfig              |  1 -
 arch/riscv/Kconfig                |  2 --
 arch/riscv/include/asm/ftrace.h   | 14 ++------------
 arch/riscv/kernel/mcount.S        | 10 +++++-----
 arch/x86/Makefile                 |  6 ------
 include/linux/compiler-clang.h    |  8 ++------
 lib/Kconfig.debug                 |  2 +-
 scripts/min-tool-version.sh       |  2 +-
 scripts/recordmcount.pl           |  2 +-
 security/Kconfig                  |  2 --
 14 files changed, 15 insertions(+), 57 deletions(-)
---
base-commit: 979741ebd48f75ed6d101c7290e3325340d361ff
change-id: 20240124-bump-min-llvm-ver-to-13-0-1-39f84dd36b19

Best regards,
-- 
Nathan Chancellor <nathan@kernel.org>

[PATCH 06/11] powerpc: Kconfig: Remove tautology in CONFIG_COMPAT

[Nathan Chancellor]

This reverts commit 6fcb574125e6 ("powerpc: Kconfig: disable
CONFIG_COMPAT for clang < 12").

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 13.0.1, this condition is always true, as the build
will fail during the configuration stage for older LLVM versions. Remove
it.

Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
Cc: mpe@ellerman.id.au
Cc: npiggin@gmail.com
Cc: aneesh.kumar@kernel.org
Cc: naveen.n.rao@linux.ibm.com
Cc: linuxppc-dev@lists.ozlabs.org
---
 arch/powerpc/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index b9fc064d38d2..86da0d01365a 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -333,7 +333,6 @@ config PANIC_TIMEOUT
 config COMPAT
 	bool "Enable support for 32bit binaries"
 	depends on PPC64
-	depends on !CC_IS_CLANG || CLANG_VERSION >= 120000
 	default y if !CPU_LITTLE_ENDIAN
 	select ARCH_WANT_OLD_COMPAT_IPC
 	select COMPAT_OLD_SIGACTION

-- 
2.43.0

Re: [PATCH 00/11] Bump the minimum supported version of LLVM to 13.0.1

[Kees Cook]

On Thu, Jan 25, 2024 at 03:55:06PM -0700, Nathan Chancellor wrote:
> Hi all,
> 
> This series bumps the minimum supported version of LLVM for building the
> kernel to 13.0.1. The first patch does the bump and all subsequent
> patches clean up all the various workarounds and checks for earlier
> versions.
> 
> Quoting the first patch's commit message for those that were only on CC
> for the clean ups:
> 
>   When __builtin_mul_overflow() has arguments that differ in terms of
>   signedness and width, LLVM may generate a libcall to __muloti4 because
>   it performs the checks in terms of 65-bit multiplication. This issue
>   becomes harder to hit (but still possible) after LLVM 12.0.0, which
>   includes a special case for matching widths but different signs.
> 
>   To gain access to this special case, which the kernel can take advantage
>   of when calls to __muloti4 appear, bump the minimum supported version of
>   LLVM for building the kernel to 13.0.1. 13.0.1 was chosen because there
>   is minimal impact to distribution support while allowing a few more
>   workarounds to be dropped in the kernel source than if 12.0.0 were
>   chosen. Looking at container images of up to date distribution versions:
> 
>     archlinux:latest              clang version 16.0.6
>     debian:oldoldstable-slim      clang version 7.0.1-8+deb10u2 (tags/RELEASE_701/final)
>     debian:oldstable-slim         Debian clang version 11.0.1-2
>     debian:stable-slim            Debian clang version 14.0.6
>     debian:testing-slim           Debian clang version 16.0.6 (19)
>     debian:unstable-slim          Debian clang version 16.0.6 (19)
>     fedora:38                     clang version 16.0.6 (Fedora 16.0.6-3.fc38)
>     fedora:latest                 clang version 17.0.6 (Fedora 17.0.6-1.fc39)
>     fedora:rawhide                clang version 17.0.6 (Fedora 17.0.6-1.fc40)
>     opensuse/leap:latest          clang version 15.0.7
>     opensuse/tumbleweed:latest    clang version 17.0.6
>     ubuntu:focal                  clang version 10.0.0-4ubuntu1
>     ubuntu:latest                 Ubuntu clang version 14.0.0-1ubuntu1.1
>     ubuntu:rolling                Ubuntu clang version 16.0.6 (15)
>     ubuntu:devel                  Ubuntu clang version 17.0.6 (3)
> 
>   The only distribution that gets left behind is Debian Bullseye, as the
>   default version is 11.0.1; other distributions either have a newer
>   version than 13.0.1 or one older than the current minimum of 11.0.0.
>   Debian has easy access to more recent LLVM versions through
>   apt.llvm.org, so this is not as much of a concern. There are also the
>   kernel.org LLVM toolchains, which should work with distributions with
>   glibc 2.28 and newer.
> 
>   Another benefit of slimming up the number of supported versions of LLVM
>   for building the kernel is reducing the build capacity needed to support
>   a matrix that builds with each supported version, which allows a matrix
>   to reallocate the freed up build capacity towards something else, such
>   as more configuration combinations.
> 
> This passes my build matrix with all supported versions.
> 
> This is based on Andrew's mm-nonmm-unstable to avoid trivial conflicts
> with my series to update the LLVM links across the repository [1] but I
> can easily rebase it to linux-kbuild if Masahiro would rather these
> patches go through there (and defer the conflict resolution to the merge
> window).
> 
> [1]: https://lore.kernel.org/20240109-update-llvm-links-v1-0-eb09b59db071@kernel.org/
> 
> ---
> Nathan Chancellor (11):
>       kbuild: Raise the minimum supported version of LLVM to 13.0.1
>       Makefile: Drop warn-stack-size plugin opt
>       x86: Drop stack-alignment plugin opt
>       ARM: Remove Thumb2 __builtin_thread_pointer workaround for Clang
>       arm64: Kconfig: Clean up tautological LLVM version checks
>       powerpc: Kconfig: Remove tautology in CONFIG_COMPAT
>       riscv: Remove MCOUNT_NAME workaround
>       riscv: Kconfig: Remove version dependency from CONFIG_CLANG_SUPPORTS_DYNAMIC_FTRACE
>       fortify: Drop Clang version check for 12.0.1 or newer
>       lib/Kconfig.debug: Update Clang version check in CONFIG_KCOV
>       compiler-clang.h: Update __diag_clang() macros for minimum version bump
> 
>  Documentation/process/changes.rst |  2 +-
>  Makefile                          |  8 --------
>  arch/arm/include/asm/current.h    |  8 +-------
>  arch/arm64/Kconfig                |  5 +----
>  arch/powerpc/Kconfig              |  1 -
>  arch/riscv/Kconfig                |  2 --
>  arch/riscv/include/asm/ftrace.h   | 14 ++------------
>  arch/riscv/kernel/mcount.S        | 10 +++++-----
>  arch/x86/Makefile                 |  6 ------
>  include/linux/compiler-clang.h    |  8 ++------
>  lib/Kconfig.debug                 |  2 +-
>  scripts/min-tool-version.sh       |  2 +-
>  scripts/recordmcount.pl           |  2 +-
>  security/Kconfig                  |  2 --
>  14 files changed, 15 insertions(+), 57 deletions(-)
> ---
> base-commit: 979741ebd48f75ed6d101c7290e3325340d361ff
> change-id: 20240124-bump-min-llvm-ver-to-13-0-1-39f84dd36b19
> 
> Best regards,
> -- 
> Nathan Chancellor <nathan@kernel.org>
> 

Yes, please. :) This looks reasonable -- I appreciate the review of
default Clang versions across distros!

Reviewed-by: Kees Cook <keescook@chromium.org>

-- 
Kees Cook

Re: [PATCH 00/11] Bump the minimum supported version of LLVM to 13.0.1

[patchwork-bot+linux-riscv]

Hello:

This series was applied to riscv/linux.git (fixes)
by Andrew Morton <akpm@linux-foundation.org>:

On Thu, 25 Jan 2024 15:55:06 -0700 you wrote:
> Hi all,
> 
> This series bumps the minimum supported version of LLVM for building the
> kernel to 13.0.1. The first patch does the bump and all subsequent
> patches clean up all the various workarounds and checks for earlier
> versions.
> 
> [...]

Here is the summary with links:
  - [07/11] riscv: Remove MCOUNT_NAME workaround
    https://git.kernel.org/riscv/c/de5f3984664e
  - [08/11] riscv: Kconfig: Remove version dependency from CONFIG_CLANG_SUPPORTS_DYNAMIC_FTRACE
    https://git.kernel.org/riscv/c/a38d97181271

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html