From patchwork Mon Jul 17 08:07:39 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kefeng Wang X-Patchwork-Id: 13316419 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from szxga02-in.huawei.com ([45.249.212.188]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qLJHJ-003PqO-1v for linux-arm-kernel@lists.infradead.org; Mon, 17 Jul 2023 08:08:36 +0000 From: Kefeng Wang Subject: [PATCH] arm64: enable dead code elimination Date: Mon, 17 Jul 2023 16:07:39 +0800 Message-ID: <20230717080739.1000460-1-wangkefeng.wang@huawei.com> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+lwn-linux-arm-kernel=archive.lwn.net@lists.infradead.org List-Archive: To: Catalin Marinas , Will Deacon Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Kefeng Wang Select CONFIG_HAVE_LD_DEAD_CODE_DATA_ELIMINATION for arm64, allowing the user to enable dead code elimination. In order for this to work, ensure that we keep the necessary tables by annotating them with KEEP, also it requires further changes to linker script to KEEP some tables and wildcard compiler generated sections into the right place. The following comparison is based 6.5-rc2 with defconfig, $ ./scripts/bloat-o-meter vmlinux-base vmlinux-new add/remove: 3/1106 grow/shrink: 4102/6964 up/down: 35704/-99980 (-64276) Function old new delta ... Total: Before=17888959, After=17824683, chg -0.36% add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-44 (-44) Data old new delta ... Total: Before=4820808, After=4820764, chg -0.00% add/remove: 0/1 grow/shrink: 0/1 up/down: 0/-1096 (-1096) RO Data old new delta ... Total: Before=5179123, After=5178027, chg -0.02% $ size vmlinux-base vmlinux text data bss dec hex filename 25433734 15385766 630656 41450156 2787aac vmlinux-base 24756738 15360870 629888 40747496 26dc1e8 vmlinux-new Memory available after booting, saving 704k on qemu, base: 8084532K/8388608K new: 8085236K/8388608K Signed-off-by: Kefeng Wang --- arch/arm64/Kconfig | 1 + arch/arm64/kernel/vmlinux.lds.S | 5 +++-- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index a2511b30d0f6..73bb908ec62f 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -148,6 +148,7 @@ config ARM64 select GENERIC_VDSO_TIME_NS select HARDIRQS_SW_RESEND select HAS_IOPORT + select HAVE_LD_DEAD_CODE_DATA_ELIMINATION select HAVE_MOVE_PMD select HAVE_MOVE_PUD select HAVE_PCI diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S index 3cd7e76cc562..bb4ce6cd6896 100644 --- a/arch/arm64/kernel/vmlinux.lds.S +++ b/arch/arm64/kernel/vmlinux.lds.S @@ -238,7 +238,7 @@ SECTIONS . = ALIGN(4); .altinstructions : { __alt_instructions = .; - *(.altinstructions) + KEEP(*(.altinstructions)) __alt_instructions_end = .; } @@ -258,8 +258,9 @@ SECTIONS INIT_CALLS CON_INITCALL INIT_RAM_FS - *(.init.altinstructions .init.bss) /* from the EFI stub */ + KEEP(*(.init.altinstructions .init.bss*)) /* from the EFI stub */ } + .exit.data : { EXIT_DATA }