[PATCH v3 0/8] LoongArch: Preliminary ClangBuiltLinux enablement

[WANG Xuerui]

From: WANG Xuerui <git@xxxxxxxxxx>

Hi,

It's been a long time since the LoongArch port was upstreamed to LLVM,
and there seems to be evidence that Linux was successfully built with
Clang inside Loongson roughly around that time; however, a lot has
changed since then, and the Linux/LoongArch codebase now makes use of
more novel features that necessitate further work. (The enablement work
is tracked at [1].)

With this patch series and a patched LLVM/Clang/LLD ([2][3][4][5]), a
working kernel can be built with `make LLVM=1`. Although currently
support for CONFIG_RELOCATABLE and CONFIG_MODULE is still TODO, we've
decided to post the series early to hopefully reduce the rebase
burden. The series contains several useful cleanups anyway.

Regarding how to merge this: because only Patch 8 is outside
arch/loongarch, I'd prefer the series to get merged through Huacai's
tree. The series applies cleanly on top of next-20230622.

Thanks go to the ClangBuiltLinux team, and LoongArch toolchain
maintainers from Loongson and the community alike; without your help
this would come much later, if at all (my free time has been steadily
dwindling this year already).

Your comments are welcome!

[1]: https://github.com/ClangBuiltLinux/linux/issues/1787
[2]: https://reviews.llvm.org/D153609
[3]: https://reviews.llvm.org/D138135
[4]: https://reviews.llvm.org/D150196
[5]: https://reviews.llvm.org/D153707

Changes in v3:

- Squashed the two CFLAGS patches into one, and removed the CC_IS_CLANG
  check in favor of a feature detection approach (Huacai and Ruoyao)
- Removed unnecessary BUILD_BUG_ONs in the invtlb wrappers, and made
  them __always_inline (Ruoyao and Bibo)
- Linked to the explanation regarding the Clang triple's "libc" part
  (Nick)
- Fixed a wrong punctuation in commit message of Patch 4

Changes in v2:

- Merged the two FCSR-related patches, now using the same approach for
  assembly and C (given that the inline asm codepath cannot be removed
  right away), also change terminology: register "class" instead of
  "bank"
- Restored signatures of invtlb wrappers for ease of rebase (potentially
  downstream product kernels?)
- Removed -G0 switches altogether (turned out it's useless upon closer
  look)
- Fix -mabi and -msoft-float handling in the CFLAGS patch; two more LLVM
  patches are now necessary (the [4] and [5] links above) but the
  original and correct CFLAGS arrangement now works

WANG Rui (2):
  LoongArch: Calculate various sizes in the linker script
  LoongArch: extable: Also recognize ABI names of registers

WANG Xuerui (6):
  LoongArch: Prepare for assemblers with proper FCSR class support
  LoongArch: Make the CPUCFG and CSR ops simple aliases of compiler
    built-ins
  LoongArch: Simplify the invtlb wrappers
  LoongArch: Tweak CFLAGS for Clang compatibility
  LoongArch: Mark Clang LTO as working
  Makefile: Add loongarch target flag for Clang compilation

 arch/loongarch/Kconfig                 |  5 ++
 arch/loongarch/Makefile                | 21 +++++---
 arch/loongarch/include/asm/fpregdef.h  |  7 +++
 arch/loongarch/include/asm/gpr-num.h   | 30 +++++++++++
 arch/loongarch/include/asm/loongarch.h | 72 +++++++-------------------
 arch/loongarch/include/asm/percpu.h    |  6 ++-
 arch/loongarch/include/asm/tlb.h       | 43 +++++++--------
 arch/loongarch/kernel/efi-header.S     |  6 +--
 arch/loongarch/kernel/head.S           |  8 +--
 arch/loongarch/kernel/traps.c          |  2 +-
 arch/loongarch/kernel/vmlinux.lds.S    |  7 +++
 arch/loongarch/lib/dump_tlb.c          |  6 +--
 arch/loongarch/vdso/Makefile           |  2 +-
 scripts/Makefile.clang                 |  1 +
 14 files changed, 118 insertions(+), 98 deletions(-)

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2.40.0