From mboxrd@z Thu Jan 1 00:00:00 1970 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 70C78C77B7A for ; Wed, 24 May 2023 11:05:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234465AbjEXLFW (ORCPT ); Wed, 24 May 2023 07:05:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39222 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234559AbjEXLFM (ORCPT ); Wed, 24 May 2023 07:05:12 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E1B931B9; Wed, 24 May 2023 04:04:58 -0700 (PDT) Received: from dggpemm500001.china.huawei.com (unknown [172.30.72.57]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4QR7ZS4FLmzLm9b; Wed, 24 May 2023 19:02:56 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemm500001.china.huawei.com (7.185.36.107) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Wed, 24 May 2023 19:04:24 +0800 Message-ID: <93960845-2af5-ac2b-c562-d8c89ad961a4@huawei.com> Date: Wed, 24 May 2023 19:04:23 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.10.1 Subject: Re: [PATCH v2 4/4] riscv: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION Content-Language: en-US To: Jisheng Zhang , Paul Walmsley , Palmer Dabbelt , Albert Ou , Arnd Bergmann CC: , , , Zhangjin Wu , Guo Ren , Bin Meng References: <20230523165502.2592-1-jszhang@kernel.org> <20230523165502.2592-5-jszhang@kernel.org> From: Kefeng Wang In-Reply-To: <20230523165502.2592-5-jszhang@kernel.org> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/5/24 0:55, Jisheng Zhang wrote: > From: Zhangjin Wu > > Select CONFIG_HAVE_LD_DEAD_CODE_DATA_ELIMINATION for RISC-V, allowing > the user to enable dead code elimination. In order for this to work, > ensure that we keep the alternative table by annotating them with KEEP. > > This boots well on qemu with both rv32_defconfig & rv64 defconfig, but > it only shrinks their builds by ~1%, a smaller config is thereforce > customized to test this feature: > > | rv32 | rv64 > --------|------------------------|--------------------- > No DCE | 4460684 | 4893488 > DCE | 3986716 | 4376400 > Shrink | 473968 (~10.6%) | 517088 (~10.5%) > > The config used above only reserves necessary options to boot on qemu > with serial console, more like the size-critical embedded scenes: > > - rv64 config: https://pastebin.com/crz82T0s > - rv32 config: rv64 config + 32-bit.config > > Here is Jisheng's original commit-msg: > When trying to run linux with various opensource riscv core on > resource limited FPGA platforms, for example, those FPGAs with less > than 16MB SDRAM, I want to save mem as much as possible. One of the > major technologies is kernel size optimizations, I found that riscv > does not currently support HAVE_LD_DEAD_CODE_DATA_ELIMINATION, which > passes -fdata-sections, -ffunction-sections to CFLAGS and passes the > --gc-sections flag to the linker. > > This not only benefits my case on FPGA but also benefits defconfigs. > Here are some notable improvements from enabling this with defconfigs: > > nommu_k210_defconfig: > text data bss dec hex > 1112009 410288 59837 1582134 182436 before > 962838 376656 51285 1390779 1538bb after > > rv32_defconfig: > text data bss dec hex > 8804455 2816544 290577 11911576 b5c198 before > 8692295 2779872 288977 11761144 b375f8 after > > defconfig: > text data bss dec hex > 9438267 3391332 485333 13314932 cb2b74 before > 9285914 3350052 483349 13119315 c82f53 after > > Signed-off-by: Zhangjin Wu > Co-developed-by: Jisheng Zhang > Signed-off-by: Jisheng Zhang > Reviewed-by: Guo Ren > Tested-by: Bin Meng Reviewed-by: Kefeng Wang > --- > arch/riscv/Kconfig | 1 + > arch/riscv/kernel/vmlinux.lds.S | 6 +++--- > 2 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > index 8f55aa4aae34..62e84fee2cfd 100644 > --- a/arch/riscv/Kconfig > +++ b/arch/riscv/Kconfig > @@ -115,6 +115,7 @@ config RISCV > select HAVE_KPROBES if !XIP_KERNEL > select HAVE_KPROBES_ON_FTRACE if !XIP_KERNEL > select HAVE_KRETPROBES if !XIP_KERNEL > + select HAVE_LD_DEAD_CODE_DATA_ELIMINATION > select HAVE_MOVE_PMD > select HAVE_MOVE_PUD > select HAVE_PCI > diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S > index e5f9f4677bbf..492dd4b8f3d6 100644 > --- a/arch/riscv/kernel/vmlinux.lds.S > +++ b/arch/riscv/kernel/vmlinux.lds.S > @@ -85,11 +85,11 @@ SECTIONS > INIT_DATA_SECTION(16) > > .init.pi : { > - *(.init.pi*) > + KEEP(*(.init.pi*)) > } > > .init.bss : { > - *(.init.bss) /* from the EFI stub */ > + KEEP(*(.init.bss*)) /* from the EFI stub */ > } > .exit.data : > { > @@ -112,7 +112,7 @@ SECTIONS > . = ALIGN(8); > .alternative : { > __alt_start = .; > - *(.alternative) > + KEEP(*(.alternative)) > __alt_end = .; > } > __init_end = .;