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 5E0F3ECAAA1 for ; Tue, 6 Sep 2022 02:16:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232901AbiIFCQt (ORCPT ); Mon, 5 Sep 2022 22:16:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54656 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230116AbiIFCQr (ORCPT ); Mon, 5 Sep 2022 22:16:47 -0400 Received: from loongson.cn (mail.loongson.cn [114.242.206.163]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C7D894DB73 for ; Mon, 5 Sep 2022 19:16:43 -0700 (PDT) Received: from [10.130.0.193] (unknown [113.200.148.30]) by localhost.localdomain (Coremail) with SMTP id AQAAf8DxBOKArRZjpVISAA--.9201S3; Tue, 06 Sep 2022 10:16:33 +0800 (CST) Subject: Re: [PATCH 1/3] LoongArch: tools: Add relocs tool support To: Xi Ruoyao , Jinyang He , Huacai Chen References: <1662113335-14282-1-git-send-email-tangyouling@loongson.cn> <1662113335-14282-2-git-send-email-tangyouling@loongson.cn> <4df8a26c49a35c1fce36d80c370f738fa71a2bef.camel@xry111.site> <78a4a6b0970c309daa336a2329e69d28df486552.camel@xry111.site> <0b2d115c42ff6cb9b8c65d852ec2f0746ca6e8d9.camel@xry111.site> Cc: linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, Xuerui Wang , Jiaxun Yang From: Youling Tang Message-ID: <29cd929b-185b-1c4b-f200-08f2a724b59d@loongson.cn> Date: Tue, 6 Sep 2022 10:16:32 +0800 User-Agent: Mozilla/5.0 (X11; Linux mips64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID: AQAAf8DxBOKArRZjpVISAA--.9201S3 X-Coremail-Antispam: 1UD129KBjvJXoWxXrW8GFWxAr15AF4rur4rKrg_yoWrJry5pr W5GayUKFsrJF17ZFW0vw10qFWSg3ykGr13Wa1rtry0yF9IvF93tw4Utr43CFy29r1ktF4j vrWYqa4I9r1rAaDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUvl14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26F1j6w1UM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4U JVWxJr1l84ACjcxK6I8E87Iv67AKxVW8Jr0_Cr1UM28EF7xvwVC2z280aVCY1x0267AKxV WxJr0_GcWle2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xvF2IEw4CE5I8CrVC2j2Wl Yx0E2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r4UMcvjeVCFs4IE7xkEbV WUJVW8JwACjcxG0xvEwIxGrwACjI8F5VA0II8E6IAqYI8I648v4I1lc7I2V7IY0VAS07Al zVAYIcxG8wCY02Avz4vE14v_Gr1l42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr 0_Gr1lx2IqxVAqx4xG67AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY 17CE14v26r126r1DMIIYrxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcV C0I7IYx2IY6xkF7I0E14v26r1j6r4UMIIF0xvE42xK8VAvwI8IcIk0rVWUJVWUCwCI42IY 6I8E87Iv67AKxVWUJVW8JwCI42IY6I8E87Iv6xkF7I0E14v26r1j6r4UYxBIdaVFxhVjvj DU0xZFpf9x0JUHWlkUUUUU= X-CM-SenderInfo: 5wdqw5prxox03j6o00pqjv00gofq/ Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Ruoyao & Jinyang On 09/05/2022 10:52 AM, Youling Tang wrote: > Hi, Ruoyao > > On 09/04/2022 12:53 AM, Xi Ruoyao wrote: >> On Sun, 2022-09-04 at 00:23 +0800, Jinyang He wrote: >>> On 2022/9/3 18:49, Xi Ruoyao wrote: >>> >>>> On Sat, 2022-09-03 at 09:57 +0800, Youling Tang wrote: >>>>>>> Unlike (pre-r6) MIPS, LoongArch has a complete support for PIC, and >>>>>>> currently LoongArch toolchain always produces PIC (except, if >>>>>>> -Wa,-mla- >>>>>>> {local,global}-with-abs or la.abs macros are used explicitly). >>>>>>> >>>>>>> So would it be easier to review and correct the uses of "la.abs" >>>>>>> in the >>>>>>> code, and make the main kernel image a real PIE? Then we can >>>>>>> load it >>>>>>> everywhere w/o any need to do relocation at load time. >>>>> At the beginning I also wanted to make the main kernel image a real >>>>> PIE >>>>> and tried it, some of the "la.abs" can be modified, but I encountered >>>>> difficulties in modifying the exception handling code part, the >>>>> kernel >>>>> will not boot after modification :(, I will continue to work hard >>>>> try. >> >>>> I just tried the same thing and get the same result :(. Will spend >>>> several hours reading the LoongArch manual about exception... >> >> The reason is the handler code is not executed in linker address, but >> copied elsewhere. Then PC-relative offset is broken. I managed to work >> around it by creating a trampoline and jump into the handler, instead of >> copy the handler code. Then I could remove most "la.abs" occurrence >> (except two in kernel entry point, which seem deliberately used): >> >> - https://github.com/xry111/linux/commit/56a433f >> - https://github.com/xry111/linux/commit/48203e6 >> > > Thank you very much. > > After applying the above two patches and the following modifications, > the relocation can be successful after removing the > apply_r_loongarch_la_rel (for la.abs relocation) implementation. I > tested it in the qemu environment. > > --- a/arch/loongarch/kernel/head.S > +++ b/arch/loongarch/kernel/head.S > @@ -113,9 +113,11 @@ SYM_CODE_START(smpboot_entry) > li.d t0, CSR_DMW1_INIT # CA, PLV0 > csrwr t0, LOONGARCH_CSR_DMWIN1 > > - la.abs t0, 0f > - jr t0 > -0: > + li.d t0, CACHE_BASE > + pcaddi t1, 0 > + or t0, t0, t1 > + jirl zero, t0, 0xc > > Youling. > >> Using the trampoline in handler table will definitely lead to sub- >> optimal performance. I just use it as a proof-of-concept. Later we may >> use some assembler trick to generate hard-coded handler table with >> correct PC-relative offsets. >> >>> The following ideas are based on experience, without validation. Patches >>> show that three types of relocation are needed to be done. >>> 1, GOT is generated by toolchain, so I think eliminating them by >>> toolchain is better. >> >> https://gcc.gnu.org/pipermail/gcc-patches/2022-September/600797.html >> >> I stop to read the mail here because it's 00:52 AM now :). >> >>> 2, Ex_table is generated but striped relocation info. We can plays pcrel >>> way to resolve this problem. One of ways like follows, (pseudo-code) Switch to relative exception tables: https://github.com/tangyouling/linux/commit/6525b8da https://github.com/tangyouling/linux/commit/b6ac0827 Will switch to the relative exception tables after applying the above two patches. So there is no need to relocate the exception table (remove relocate_exception_table). Now we can remove the relocation of la.abs , got and ex_table, but still need to relocate LARCH_64. Is there anything else that needs to be modified to eliminate this relocation? Thanks, Youling. >> >> /* snip */ >> >> >