FROMLIST: 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%.
Bug: 145210207
Change-Id: Ief7053b55f99f7be0da8a01b6c4edb0a9e41ee07
Link: https://lore.kernel.org/lkml/20201211184633.3213045-1-samitolvanen@google.com/
Suggested-by: George Burgess IV <gbiv@google.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
diff --git a/Makefile b/Makefile
index 439d94c..af889a9 100644
--- a/Makefile
+++ b/Makefile
@@ -902,6 +902,9 @@
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