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Subject[PATCH v4 14/29] kbuild: lto: limit inlining
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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>
---
Makefile | 3 +++
1 file changed, 3 insertions(+)

diff --git a/Makefile b/Makefile
index 23cdb475c445..d6510ee99ffc 100644
--- a/Makefile
+++ b/Makefile
@@ -894,6 +894,9 @@ else
CC_FLAGS_LTO += -flto
endif
CC_FLAGS_LTO += -fvisibility=default
+
+# Limit inlining across translation units to reduce binary size
+KBUILD_LDFLAGS += -mllvm -import-instr-limit=5
endif

ifdef CONFIG_LTO
--
2.28.0.709.gb0816b6eb0-goog
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