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From: Sami Tolvanen <samitolvanen@google.com>
To: Masahiro Yamada <masahiroy@kernel.org>,
	Will Deacon <will@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Kees Cook <keescook@chromium.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	clang-built-linux@googlegroups.com,
	kernel-hardening@lists.openwall.com, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, x86@kernel.org,
	Sami Tolvanen <samitolvanen@google.com>
Subject: [PATCH v5 12/29] kbuild: lto: limit inlining
Date: Fri,  9 Oct 2020 09:13:21 -0700
Message-ID: <20201009161338.657380-13-samitolvanen@google.com> (raw)
In-Reply-To: <20201009161338.657380-1-samitolvanen@google.com>

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 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
-- 
2.28.0.1011.ga647a8990f-goog


  parent reply index

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-09 16:13 [PATCH v5 00/29] Add support for Clang LTO Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 01/29] kbuild: preprocess module linker script Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 02/29] objtool: Add a pass for generating __mcount_loc Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 03/29] objtool: Don't autodetect vmlinux.o Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 04/29] tracing: move function tracer options to Kconfig Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 05/29] tracing: add support for objtool mcount Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 06/29] x86, build: use " Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 07/29] treewide: remove DISABLE_LTO Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 08/29] kbuild: add support for Clang LTO Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 09/29] kbuild: lto: fix module versioning Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 10/29] objtool: Split noinstr validation from --vmlinux Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 11/29] kbuild: lto: postpone objtool Sami Tolvanen
2020-10-09 16:13 ` Sami Tolvanen [this message]
2020-10-09 16:13 ` [PATCH v5 13/29] kbuild: lto: merge module sections Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 14/29] kbuild: lto: remove duplicate dependencies from .mod files Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 15/29] init: lto: ensure initcall ordering Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 16/29] init: lto: fix PREL32 relocations Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 17/29] PCI: Fix PREL32 relocations for LTO Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 18/29] modpost: lto: strip .lto from module names Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 19/29] scripts/mod: disable LTO for empty.c Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 20/29] efi/libstub: disable LTO Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 21/29] drivers/misc/lkdtm: disable LTO for rodata.o Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 22/29] arm64: vdso: disable LTO Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 23/29] KVM: arm64: disable LTO for the nVHE directory Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 24/29] arm64: disable recordmcount with DYNAMIC_FTRACE_WITH_REGS Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 25/29] arm64: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-10-12  8:31   ` Will Deacon
2020-10-12 20:44     ` Kees Cook
2020-10-12 20:51       ` Will Deacon
2020-10-12 21:02         ` Kees Cook
2020-10-09 16:13 ` [PATCH v5 26/29] x86/asm: annotate indirect jumps Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 27/29] x86, vdso: disable LTO only for vDSO Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 28/29] x86, cpu: disable LTO for cpu.c Sami Tolvanen
2020-10-09 16:13 ` [PATCH v5 29/29] x86, build: allow LTO_CLANG and THINLTO to be selected Sami Tolvanen
2020-10-09 16:30 ` [PATCH v5 00/29] Add support for Clang LTO Sedat Dilek
2020-10-09 20:50   ` Sami Tolvanen
     [not found] ` <20201009153512.1546446a@gandalf.local.home>
2020-10-09 21:05   ` Sami Tolvanen
2020-10-09 23:38     ` Steven Rostedt
2020-10-10  0:00       ` Sami Tolvanen

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