diff options
| author | Wende Tan <twd2.me@gmail.com> | 2023-10-17 15:21:04 -0700 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2024-01-22 10:06:29 -0800 |
| commit | 021d23428bdbae032294e8f4a29cb53cb50ae71c (patch) | |
| tree | d02f238ccfb362b7784fd20a17918e9f5b75d519 /arch/riscv/Makefile | |
| parent | 3a6dd5f614a13033a47eaf439ac34e7b6fbc7705 (diff) | |
RISC-V: build: Allow LTO to be selected
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>
Diffstat (limited to 'arch/riscv/Makefile')
| -rw-r--r-- | arch/riscv/Makefile | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile index 0b7d109258e7..252d63942f34 100644 --- a/arch/riscv/Makefile +++ b/arch/riscv/Makefile @@ -50,6 +50,11 @@ ifndef CONFIG_AS_IS_LLVM KBUILD_CFLAGS += -Wa,-mno-relax KBUILD_AFLAGS += -Wa,-mno-relax endif +# LLVM has an issue with target-features and LTO: https://github.com/llvm/llvm-project/issues/59350 +# Ensure it is aware of linker relaxation with LTO, otherwise relocations may +# be incorrect: https://github.com/llvm/llvm-project/issues/65090 +else ifeq ($(CONFIG_LTO_CLANG),y) + KBUILD_LDFLAGS += -mllvm -mattr=+c -mllvm -mattr=+relax endif ifeq ($(CONFIG_SHADOW_CALL_STACK),y) |