diff options
| author | Wende Tan <twd2.me@gmail.com> | 2023-10-18 00:21:04 +0200 |
|---|---|---|
| committer | Palmer Dabbelt <palmer@rivosinc.com> | 2024-01-22 19:06:29 +0100 |
| commit | 021d23428bdbae032294e8f4a29cb53cb50ae71c (patch) | |
| tree | d02f238ccfb362b7784fd20a17918e9f5b75d519 /arch | |
| parent | riscv: remove unneeded #include <asm-generic/export.h> (diff) | |
| download | linux-021d23428bdbae032294e8f4a29cb53cb50ae71c.tar.xz linux-021d23428bdbae032294e8f4a29cb53cb50ae71c.zip | |
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')
| -rw-r--r-- | arch/riscv/Kconfig | 3 | ||||
| -rw-r--r-- | arch/riscv/Makefile | 5 | ||||
| -rw-r--r-- | arch/riscv/kernel/pi/Makefile | 3 |
3 files changed, 11 insertions, 0 deletions
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index bffbd869a068..60c8fd1a677f 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -47,6 +47,9 @@ config RISCV select ARCH_SUPPORTS_CFI_CLANG select ARCH_SUPPORTS_DEBUG_PAGEALLOC if MMU select ARCH_SUPPORTS_HUGETLBFS if MMU + # LLD >= 14: https://github.com/llvm/llvm-project/issues/50505 + select ARCH_SUPPORTS_LTO_CLANG if LLD_VERSION >= 140000 + select ARCH_SUPPORTS_LTO_CLANG_THIN if LLD_VERSION >= 140000 select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU select ARCH_SUPPORTS_PER_VMA_LOCK if MMU select ARCH_SUPPORTS_SHADOW_CALL_STACK if HAVE_SHADOW_CALL_STACK 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) diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile index 07915dc9279e..b75f150b923d 100644 --- a/arch/riscv/kernel/pi/Makefile +++ b/arch/riscv/kernel/pi/Makefile @@ -9,6 +9,9 @@ KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) -fpie \ -fno-asynchronous-unwind-tables -fno-unwind-tables \ $(call cc-option,-fno-addrsig) +# Disable LTO +KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_LTO), $(KBUILD_CFLAGS)) + KBUILD_CFLAGS += -mcmodel=medany CFLAGS_cmdline_early.o += -D__NO_FORTIFY |