kbuild: lto: limit inlining
This change limits function inlining across translation unit boundaries
in order to reduce the binary size with LTO. The -import-instr-limit
flag defines a size limit, as the number of LLVM IR instructions, for
importing functions from other TUs, defaulting to 100.
Based on testing with arm64 defconfig, we found that a limit of 5 is a
reasonable compromise between performance and binary size, reducing the
size of a stripped vmlinux by 11%.
Suggested-by: George Burgess IV <gbiv@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201211184633.3213045-5-samitolvanen@google.com
diff --git a/Makefile b/Makefile
index 173a7c9..668909e 100644
--- a/Makefile
+++ b/Makefile
@@ -901,6 +901,9 @@
CC_FLAGS_LTO += -flto
endif
CC_FLAGS_LTO += -fvisibility=hidden
+
+# Limit inlining across translation units to reduce binary size
+KBUILD_LDFLAGS += -mllvm -import-instr-limit=5
endif
ifdef CONFIG_LTO