021d23428b
Allow LTO to be selected for RISC-V, only when LLD >= 14, since there is an issue [1] in prior LLD versions that prevents LLD to generate proper machine code for RISC-V when writing `nop`s. To avoid boot failures in QEMU [2], '-mattr=+c' and '-mattr=+relax' need to be passed via '-mllvm' to ld.lld, as there appears to be an issue with LLVM's target-features and LTO [3], which can result in incorrect relocations to branch targets [4]. Once this is fixed in LLVM, it can be made conditional on affected ld.lld versions. Disable LTO for arch/riscv/kernel/pi, as llvm-objcopy expects an ELF object file when manipulating the files in that subfolder, rather than LLVM bitcode. [1] https://github.com/llvm/llvm-project/issues/50505, resolved by LLVM commit e63455d5e0e5 ("[MC] Use local MCSubtargetInfo in writeNops") [2] https://github.com/ClangBuiltLinux/linux/issues/1942 [3] https://github.com/llvm/llvm-project/issues/59350 [4] https://github.com/llvm/llvm-project/issues/65090 Tested-by: Wende Tan <twd2.me@gmail.com> Signed-off-by: Wende Tan <twd2.me@gmail.com> Co-developed-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Nathan Chancellor <nathan@kernel.org> Reviewed-by: Conor Dooley <conor.dooley@microchip.com> Link: https://lore.kernel.org/r/20231017-riscv-lto-v4-1-e7810b24e805@kernel.org Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.