From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from loongson.cn (mail.loongson.cn [114.242.206.163]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 12283EC6 for ; Thu, 28 Jul 2022 01:03:07 +0000 (UTC) Received: from localhost.localdomain (unknown [111.9.175.10]) by mail.loongson.cn (Coremail) with SMTP id AQAAf9Dxz9JB4OFiEr49AA--.23298S3; Thu, 28 Jul 2022 09:02:58 +0800 (CST) Subject: Re: [PATCH 3/5] LoongArch: Support relocation against _GLOBAL_OFFSET_TABLE_ To: Xi Ruoyao , loongarch@lists.linux.dev References: <385f63bcbee8e37c42f479ce9cdc7e7d731d419b.camel@xry111.site> <99733532831377ab6585d43ee40bf314a2d4c5a3.camel@xry111.site> Cc: linux-kernel@vger.kernel.org, WANG Xuerui , Huacai Chen From: Jinyang He Message-ID: <10c1e0f9-8409-a0f4-9b18-a5f56dfb14e1@loongson.cn> Date: Thu, 28 Jul 2022 09:02:57 +0800 User-Agent: Mozilla/5.0 (X11; Linux mips64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 Precedence: bulk X-Mailing-List: loongarch@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <99733532831377ab6585d43ee40bf314a2d4c5a3.camel@xry111.site> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-CM-TRANSID:AQAAf9Dxz9JB4OFiEr49AA--.23298S3 X-Coremail-Antispam: 1UD129KBjvJXoW7tF1xZFyDKr13uFWfXw4UXFb_yoW5JFyxpF Wqk395Wr4fCr1DG3Z3Z3WkuFy5GFZ7Gr4jgFW7G345Aw1jqryFyayxKryq9a18X34kC3y0 qr1rWFW7Kan7ArUanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkvb7Iv0xC_Kw4lb4IE77IF4wAFF20E14v26r1j6r4UM7CY07I2 0VC2zVCF04k26cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rw A2F7IY1VAKz4vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Gr0_Xr1l84ACjcxK6xII jxv20xvEc7CjxVAFwI0_Gr0_Cr1l84ACjcxK6I8E87Iv67AKxVWxJVW8Jr1l84ACjcxK6I 8E87Iv6xkF7I0E14v26r4UJVWxJr1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xv F2IEw4CE5I8CrVC2j2WlYx0E2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r 4UMcvjeVCFs4IE7xkEbVWUJVW8JwACjcxG0xvEwIxGrwCYjI0SjxkI62AI1cAE67vIY487 MxAIw28IcxkI7VAKI48JMxC20s026xCaFVCjc4AY6r1j6r4UMI8I3I0E5I8CrVAFwI0_Jr 0_Jr4lx2IqxVCjr7xvwVAFwI0_JrI_JrWlx4CE17CEb7AF67AKxVWUAVWUtwCIc40Y0x0E wIxGrwCI42IY6xIIjxv20xvE14v26r1j6r1xMIIF0xvE2Ix0cI8IcVCY1x0267AKxVWUJV W8JwCI42IY6xAIw20EY4v20xvaj40_WFyUJVCq3wCI42IY6I8E87Iv67AKxVWUJVW8JwCI 42IY6I8E87Iv6xkF7I0E14v26r1j6r4UYxBIdaVFxhVjvjDU0xZFpf9x07bOoGdUUUUU= X-CM-SenderInfo: pkhmx0p1dqwqxorr0wxvrqhubq/ On 07/28/2022 12:28 AM, Xi Ruoyao wrote: > With the stack-based relocations, the assembler emits three relocations > to push the PC-relative offset of a GOT entry: > > R_LARCH_SOP_PUSH_PCREL _GLOBAL_OFFSET_TABLE_ > R_LARCH_SOP_PUSH_GPREL foo > R_LARCH_SOP_ADD > > "_GLOBAL_OFFSET_TABLE_" does not really exist in the symtab and the BFD > linker handles it with special hack. Implement a similar hack for > kernel so we will be able to really use R_LARCH_SOP_PUSH_GPREL > relocation. > > Signed-off-by: Xi Ruoyao > --- > arch/loongarch/kernel/module-sections.c | 21 +++++++++++++++++++++ > 1 file changed, 21 insertions(+) > > diff --git a/arch/loongarch/kernel/module-sections.c b/arch/loongarch/kernel/module-sections.c > index 509c0b86b1e9..73976addbf60 100644 > --- a/arch/loongarch/kernel/module-sections.c > +++ b/arch/loongarch/kernel/module-sections.c > @@ -89,6 +89,9 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > char *secstrings, struct module *mod) > { > unsigned int i, num_plts = 0, num_gots = 0; > + Elf_Shdr *symtab = NULL; > + Elf_Sym *symbols; > + char *strings; > > /* > * Find the empty .plt sections. > @@ -100,6 +103,8 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > mod->arch.plt_idx.shdr = sechdrs + i; > else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got")) > mod->arch.got.shdr = sechdrs + i; > + else if (sechdrs[i].sh_type == SHT_SYMTAB) > + symtab = sechdrs + i; > } > > if (!mod->arch.plt.shdr) { > @@ -115,6 +120,22 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, > return -ENOEXEC; > } > > + if (!symtab) { > + pr_err("%s: module symbol table missing\n", mod->name); > + return -ENOEXEC; > + } > + > + symbols = (void *) ehdr + symtab->sh_offset; > + strings = (void *) ehdr + sechdrs[symtab->sh_link].sh_offset; > + > + for (i = 0; i < symtab->sh_size / sizeof(Elf_Sym); i++) > + if (symbols[i].st_shndx == SHN_UNDEF && > + strcmp(strings + symbols[i].st_name, > + "_GLOBAL_OFFSET_TABLE_") == 0) { > + symbols[i].st_shndx = mod->arch.got.shdr - sechdrs; > + symbols[i].st_value = 0; > + } > + > /* Calculate the maxinum number of entries */ > for (i = 0; i < ehdr->e_shnum; i++) { > int num_rela = sechdrs[i].sh_size / sizeof(Elf_Rela); Hi, Ruoyao, It is possible to create a symbol when linking, which means maybe we can add _GLOBAL_OFFSET_TABLE_ in 'module.lds.h'. What do you think about it? Thanks, Jinyang