Thread (212 messages) 212 messages, 19 authors, 2020-09-10
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[PATCH 06/22] kbuild: lto: limit inlining

From: Sami Tolvanen <samitolvanen@google.com>
Date: 2020-06-24 20:33:18
Also in: linux-arch, linux-kbuild, linux-pci, lkml
Subsystem: kernel build + files below scripts/ (unless maintained elsewhere), the rest · Maintainers: Nathan Chancellor, Nicolas Schier, Linus Torvalds

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.
The default value is 100, and decreasing it to 5 reduces the size
of a stripped arm64 defconfig vmlinux by 11%.

Suggested-by: George Burgess IV <redacted>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
---
 Makefile | 4 ++++
 1 file changed, 4 insertions(+)
diff --git a/Makefile b/Makefile
index 3a7e5e5c17b9..ee66513a5b66 100644
--- a/Makefile
+++ b/Makefile
@@ -894,6 +894,10 @@ else
 CC_FLAGS_LTO_CLANG := -flto
 endif
 CC_FLAGS_LTO_CLANG += -fvisibility=default
+
+# Limit inlining across translation units to reduce binary size
+LD_FLAGS_LTO_CLANG := -mllvm -import-instr-limit=5
+KBUILD_LDFLAGS += $(LD_FLAGS_LTO_CLANG)
 endif
 
 ifdef CONFIG_LTO
-- 
2.27.0.212.ge8ba1cc988-goog


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