path: root/arch/Kconfig
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authorLinus Torvalds <>2021-02-23 09:28:51 -0800
committerLinus Torvalds <>2021-02-23 09:28:51 -0800
commit79db4d2293eba2ce6265a341bedf6caecad5eeb3 (patch)
treef575b2356ab0e44e44909260379dff1d719aa659 /arch/Kconfig
parent3b9cdafb5358eb9f3790de2f728f765fef100731 (diff)
parent2b8689520520175075ca97bc4eaf51ff3f7253aa (diff)
Merge tag 'clang-lto-v5.12-rc1' of git://
Pull clang LTO updates from Kees Cook: "Clang Link Time Optimization. This is built on the work done preparing for LTO by arm64 folks, tracing folks, etc. This includes the core changes as well as the remaining pieces for arm64 (LTO has been the default build method on Android for about 3 years now, as it is the prerequisite for the Control Flow Integrity protections). While x86 LTO enablement is done, it depends on some pending objtool clean-ups. It's possible that I'll send a "part 2" pull request for LTO that includes x86 support. For merge log posterity, and as detailed in commit dc5723b02e52 ("kbuild: add support for Clang LTO"), here is the lt;dr to do an LTO build: make LLVM=1 LLVM_IAS=1 defconfig scripts/config -e LTO_CLANG_THIN make LLVM=1 LLVM_IAS=1 (To do a cross-compile of arm64, add "CROSS_COMPILE=aarch64-linux-gnu-" and "ARCH=arm64" to the "make" command lines.) Summary: - Clang LTO build infrastructure and arm64-specific enablement (Sami Tolvanen) - Recursive build CC_FLAGS_LTO fix (Alexander Lobakin)" * tag 'clang-lto-v5.12-rc1' of git:// kbuild: prevent CC_FLAGS_LTO self-bloating on recursive rebuilds arm64: allow LTO to be selected arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS arm64: vdso: disable LTO drivers/misc/lkdtm: disable LTO for rodata.o efi/libstub: disable LTO scripts/mod: disable LTO for empty.c modpost: lto: strip .lto from module names PCI: Fix PREL32 relocations for LTO init: lto: fix PREL32 relocations init: lto: ensure initcall ordering kbuild: lto: add a default list of used symbols kbuild: lto: merge module sections kbuild: lto: limit inlining kbuild: lto: fix module versioning kbuild: add support for Clang LTO tracing: move function tracer options to Kconfig
Diffstat (limited to 'arch/Kconfig')
1 files changed, 90 insertions, 0 deletions
diff --git a/arch/Kconfig b/arch/Kconfig
index 9fc4eb8bfdbc..207261f4879d 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -603,6 +603,96 @@ config SHADOW_CALL_STACK
reading and writing arbitrary memory may be able to locate them
and hijack control flow by modifying the stacks.
+config LTO
+ bool
+ help
+ Selected if the kernel will be built using the compiler's LTO feature.
+config LTO_CLANG
+ bool
+ select LTO
+ help
+ Selected if the kernel will be built using Clang's LTO feature.
+ bool
+ help
+ An architecture should select this option if it supports:
+ - compiling with Clang,
+ - compiling inline assembly with Clang's integrated assembler,
+ - and linking with LLD.
+ bool
+ help
+ An architecture should select this option if it can support Clang's
+ ThinLTO mode.
+ def_bool y
+ # Clang >= 11:
+ depends on CC_IS_CLANG && CLANG_VERSION >= 110000 && LD_IS_LLD
+ depends on $(success,test $(LLVM) -eq 1)
+ depends on $(success,test $(LLVM_IAS) -eq 1)
+ depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
+ depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
+ depends on !KASAN
+ depends on !GCOV_KERNEL
+ help
+ The compiler and Kconfig options support building with Clang's
+ LTO.
+ prompt "Link Time Optimization (LTO)"
+ default LTO_NONE
+ help
+ This option enables Link Time Optimization (LTO), which allows the
+ compiler to optimize binaries globally.
+ If unsure, select LTO_NONE. Note that LTO is very resource-intensive
+ so it's disabled by default.
+config LTO_NONE
+ bool "None"
+ help
+ Build the kernel normally, without Link Time Optimization (LTO).
+ bool "Clang Full LTO (EXPERIMENTAL)"
+ depends on HAS_LTO_CLANG
+ depends on !COMPILE_TEST
+ select LTO_CLANG
+ help
+ This option enables Clang's full Link Time Optimization (LTO), which
+ allows the compiler to optimize the kernel globally. If you enable
+ this option, the compiler generates LLVM bitcode instead of ELF
+ object files, and the actual compilation from bitcode happens at
+ the LTO link step, which may take several minutes depending on the
+ kernel configuration. More information can be found from LLVM's
+ documentation:
+ During link time, this option can use a large amount of RAM, and
+ may take much longer than the ThinLTO option.
+ bool "Clang ThinLTO (EXPERIMENTAL)"
+ select LTO_CLANG
+ help
+ This option enables Clang's ThinLTO, which allows for parallel
+ optimization and faster incremental compiles compared to the
+ CONFIG_LTO_CLANG_FULL option. More information can be found
+ from Clang's documentation:
+ If unsure, say Y.