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[v5,12/29] kbuild: lto: limit inlining

Message ID 20201009161338.657380-13-samitolvanen@google.com
State New, archived
Headers show
Series Add support for Clang LTO | expand

Commit Message

Sami Tolvanen Oct. 9, 2020, 4:13 p.m. UTC
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(+)
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Patch

diff --git a/Makefile b/Makefile
index 6d31a78d79ce..3fe2dca17261 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