[v4,0/2] infer --target from SRCARCH for CC=clang

Message

Nick Desaulniers July 30, 2021, 8:16 p.m. UTC

We get constant feedback that the command line invocation of make is too
long. CROSS_COMPILE is helpful when a toolchain has a prefix of the
target triple, or is an absolute path outside of $PATH, but it's mostly
redundant for a given ARCH.

Instead, let's infer it from SRCARCH, and move some flag handling into a
new file included from the top level Makefile.

Changes v3 -> v4:
* Remove the requirement that LLVM_IAS=1 be set, as per Masahiro.
* Remove the Documentation/ change from patch 2, as per Masahiro and
  Nathan.
* Add Documentation/ change as patch 3, from Masahiro.
* Reword commit message of patch 2, as per Nathan.
* Change patch 2 oneline to refer to --target and CC=clang (not
  CROSS_COMPILE).
* Carry Arnd's and Nathan's AB/RB/TB tags, confirmed ok on IRC+discord.

Changes v2 -> v3:
* Remove requirement that LLVM=1 be set. Instead, if building with just
  CC=clang LLVM_IAS=1 instead of LLVM=1 LLVM_IAS=1, you should use
  LD=ld.lld explicitly, or LD=aarch64-linux-gnu-ld. (As per Masahiro)
  Example:

  $ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=ld.lld OBJCOPY=llvm-objcopy \
    STRIP=llvm-strip -j72 defconfig all

  (It's still preferable to use LLVM=1 IMO, but this is maximally
  flexible.)
* Change oneliner from LLVM=1 to CC=clang.
* Update Docs slightly.

Changes v1 -> v2:
* patch 1/2 untouched.
* Fix typos in commit message as per Geert and Masahiro.
* Use SRCARCH instead of ARCH, simplifying x86 handling, as per
  Masahiro. Add his sugguested by tag.
* change commit oneline from 'drop' to 'infer.'
* Add detail about explicit host --target and relationship of ARCH to
  SRCARCH, as per Masahiro.

*** BLURB HERE ***

Nick Desaulniers (2):
  Makefile: infer --target from ARCH for CC=clang
  Documentation/llvm: update CROSS_COMPILE inferencing

 Documentation/kbuild/llvm.rst | 17 +++++++++++++++++
 scripts/Makefile.clang        | 30 ++++++++++++++++++++++++++++--
 2 files changed, 45 insertions(+), 2 deletions(-)


base-commit: 27932b6a2088eac7a5afa5471963b926cfbb4de7
prerequisite-patch-id: 0d3072ecb5fd06ff6fd6ea81fe601f6c54c23910

Comments

Nick Desaulniers July 30, 2021, 9:54 p.m. UTC | #1

On Fri, Jul 30, 2021 at 1:17 PM Nick Desaulniers
<[e-mail]> wrote:
>
> We get constant feedback that the command line invocation of make is too
> long. CROSS_COMPILE is helpful when a toolchain has a prefix of the
> target triple, or is an absolute path outside of $PATH, but it's mostly
> redundant for a given ARCH.
>
> Instead, let's infer it from SRCARCH, and move some flag handling into a
> new file included from the top level Makefile.
>
> Changes v3 -> v4:
> * Remove the requirement that LLVM_IAS=1 be set, as per Masahiro.
> * Remove the Documentation/ change from patch 2, as per Masahiro and
>   Nathan.
> * Add Documentation/ change as patch 3, from Masahiro.
> * Reword commit message of patch 2, as per Nathan.
> * Change patch 2 oneline to refer to --target and CC=clang (not
>   CROSS_COMPILE).
> * Carry Arnd's and Nathan's AB/RB/TB tags, confirmed ok on IRC+discord.
>
> Changes v2 -> v3:
> * Remove requirement that LLVM=1 be set. Instead, if building with just
>   CC=clang LLVM_IAS=1 instead of LLVM=1 LLVM_IAS=1, you should use
>   LD=ld.lld explicitly, or LD=aarch64-linux-gnu-ld. (As per Masahiro)
>   Example:
>
>   $ ARCH=arm64 make CC=clang LLVM_IAS=1 LD=ld.lld OBJCOPY=llvm-objcopy \
>     STRIP=llvm-strip -j72 defconfig all
>
>   (It's still preferable to use LLVM=1 IMO, but this is maximally
>   flexible.)
> * Change oneliner from LLVM=1 to CC=clang.
> * Update Docs slightly.
>
> Changes v1 -> v2:
> * patch 1/2 untouched.
> * Fix typos in commit message as per Geert and Masahiro.
> * Use SRCARCH instead of ARCH, simplifying x86 handling, as per
>   Masahiro. Add his sugguested by tag.
> * change commit oneline from 'drop' to 'infer.'
> * Add detail about explicit host --target and relationship of ARCH to
>   SRCARCH, as per Masahiro.
>
> *** BLURB HERE ***

Err, sorry, it looks like I did:
$ git format-patch HEAD~2 ...
when I meant to do HEAD~3 ..., will resend.

>
> Nick Desaulniers (2):
>   Makefile: infer --target from ARCH for CC=clang
>   Documentation/llvm: update CROSS_COMPILE inferencing
>
>  Documentation/kbuild/llvm.rst | 17 +++++++++++++++++
>  scripts/Makefile.clang        | 30 ++++++++++++++++++++++++++++--
>  2 files changed, 45 insertions(+), 2 deletions(-)
>
>
> base-commit: 27932b6a2088eac7a5afa5471963b926cfbb4de7
> prerequisite-patch-id: 0d3072ecb5fd06ff6fd6ea81fe601f6c54c23910
> --
> 2.32.0.554.ge1b32706d8-goog
>