ARM: Reduce __thumb2__ definition to crypto files that require it

Commit 1d2e9b67b001 ("ARM: 9265/1: pass -march= only to compiler") added
a __thumb2__ define to ASFLAGS to avoid build errors in the crypto code,
which relies on __thumb2__ for preprocessing. Commit 59e2cf8d21e0 ("ARM:
9275/1: Drop '-mthumb' from AFLAGS_ISA") followed up on this by removing
-mthumb from AFLAGS so that __thumb2__ would not be defined when the
default target was ARMv7 or newer.

Unfortunately, the second commit's fix assumes that the toolchain
defaults to -mno-thumb / -marm, which is not the case for Debian's
arm-linux-gnueabihf target, which defaults to -mthumb:

  $ echo | arm-linux-gnueabihf-gcc -dM -E - | grep __thumb
  #define __thumb2__ 1
  #define __thumb__ 1

This target is used by several CI systems, which will still see
redefined macro warnings, despite '-mthumb' not being present in the
flags:

  <command-line>: warning: "__thumb2__" redefined
  <built-in>: note: this is the location of the previous definition

Remove the global AFLAGS __thumb2__ define and move it to the crypto
folder where it is required by the imported OpenSSL algorithms; the rest
of the kernel should use the internal CONFIG_THUMB2_KERNEL symbol to
know whether or not Thumb2 is being used or not. Be sure that __thumb2__
is undefined first so that there are no macro redefinition warnings.

Link: https://github.com/ClangBuiltLinux/linux/issues/1772
Reported-by: "kernelci.org bot" <bot@kernelci.org>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 arch/arm/Makefile        | 2 +-
 arch/arm/crypto/Makefile | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)


base-commit: 71a7507afbc3f27c346898f13ab9bfd918613c34

On Thu, Dec 22, 2022 at 11:52:27AM -0800, Nick Desaulniers wrote:
> On Thu, Dec 22, 2022 at 11:30 AM Nathan Chancellor <nathan@kernel.org> wrote:
> >
> > Commit 1d2e9b67b001 ("ARM: 9265/1: pass -march= only to compiler") added
> > a __thumb2__ define to ASFLAGS to avoid build errors in the crypto code,
> > which relies on __thumb2__ for preprocessing. Commit 59e2cf8d21e0 ("ARM:
> > 9275/1: Drop '-mthumb' from AFLAGS_ISA") followed up on this by removing
> > -mthumb from AFLAGS so that __thumb2__ would not be defined when the
> > default target was ARMv7 or newer.
> >
> > Unfortunately, the second commit's fix assumes that the toolchain
> > defaults to -mno-thumb / -marm, which is not the case for Debian's
> > arm-linux-gnueabihf target, which defaults to -mthumb:
> >
> >   $ echo | arm-linux-gnueabihf-gcc -dM -E - | grep __thumb
> >   #define __thumb2__ 1
> >   #define __thumb__ 1
> 
> Interesting, that was hard to foresee in review of 1d2e9b67b001 and
> 59e2cf8d21e0.
> 
> FWIW, their non-hf target does not.
> $ echo | arm-linux-gnueabi-gcc -dM -E - | grep __thumb
> $
> 
> >
> > This target is used by several CI systems, which will still see
> > redefined macro warnings, despite '-mthumb' not being present in the
> > flags:
> >
> >   <command-line>: warning: "__thumb2__" redefined
> >   <built-in>: note: this is the location of the previous definition
> >
> > Remove the global AFLAGS __thumb2__ define and move it to the crypto
> > folder where it is required by the imported OpenSSL algorithms; the rest
> > of the kernel should use the internal CONFIG_THUMB2_KERNEL symbol to
> > know whether or not Thumb2 is being used or not. Be sure that __thumb2__
> > is undefined first so that there are no macro redefinition warnings.
> >
> > Link: https://github.com/ClangBuiltLinux/linux/issues/1772
> > Reported-by: "kernelci.org bot" <bot@kernelci.org>
> > Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> 
> Thanks Nathan and Ard.

Shouldn't this also have a fixes tag?

On Mon, Jan 23, 2023 at 10:48:24AM +0000, Russell King (Oracle) wrote:
> On Thu, Dec 22, 2022 at 11:52:27AM -0800, Nick Desaulniers wrote:
> > On Thu, Dec 22, 2022 at 11:30 AM Nathan Chancellor <nathan@kernel.org> wrote:
> > >
> > > Commit 1d2e9b67b001 ("ARM: 9265/1: pass -march= only to compiler") added
> > > a __thumb2__ define to ASFLAGS to avoid build errors in the crypto code,
> > > which relies on __thumb2__ for preprocessing. Commit 59e2cf8d21e0 ("ARM:
> > > 9275/1: Drop '-mthumb' from AFLAGS_ISA") followed up on this by removing
> > > -mthumb from AFLAGS so that __thumb2__ would not be defined when the
> > > default target was ARMv7 or newer.
> > >
> > > Unfortunately, the second commit's fix assumes that the toolchain
> > > defaults to -mno-thumb / -marm, which is not the case for Debian's
> > > arm-linux-gnueabihf target, which defaults to -mthumb:
> > >
> > >   $ echo | arm-linux-gnueabihf-gcc -dM -E - | grep __thumb
> > >   #define __thumb2__ 1
> > >   #define __thumb__ 1
> > 
> > Interesting, that was hard to foresee in review of 1d2e9b67b001 and
> > 59e2cf8d21e0.
> > 
> > FWIW, their non-hf target does not.
> > $ echo | arm-linux-gnueabi-gcc -dM -E - | grep __thumb
> > $
> > 
> > >
> > > This target is used by several CI systems, which will still see
> > > redefined macro warnings, despite '-mthumb' not being present in the
> > > flags:
> > >
> > >   <command-line>: warning: "__thumb2__" redefined
> > >   <built-in>: note: this is the location of the previous definition
> > >
> > > Remove the global AFLAGS __thumb2__ define and move it to the crypto
> > > folder where it is required by the imported OpenSSL algorithms; the rest
> > > of the kernel should use the internal CONFIG_THUMB2_KERNEL symbol to
> > > know whether or not Thumb2 is being used or not. Be sure that __thumb2__
> > > is undefined first so that there are no macro redefinition warnings.
> > >
> > > Link: https://github.com/ClangBuiltLinux/linux/issues/1772
> > > Reported-by: "kernelci.org bot" <bot@kernelci.org>
> > > Suggested-by: Ard Biesheuvel <ardb@kernel.org>
> > > Signed-off-by: Nathan Chancellor <nathan@kernel.org>
> > 
> > Thanks Nathan and Ard.
> 
> Shouldn't this also have a fixes tag?

Ugh, yes, sorry about that :( would you kind taking these when you apply
the patch or would you like me to resubmit?

Fixes: 59e2cf8d21e0 ("ARM: 9275/1: Drop '-mthumb' from AFLAGS_ISA")
Fixes: 1d2e9b67b001 ("ARM: 9265/1: pass -march= only to compiler")

Cheers,
Nathan