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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C0C24C43217 for ; Fri, 19 Nov 2021 02:10:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A595361A89 for ; Fri, 19 Nov 2021 02:10:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233890AbhKSCNB (ORCPT ); Thu, 18 Nov 2021 21:13:01 -0500 Received: from szxga02-in.huawei.com ([45.249.212.188]:26329 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233873AbhKSCNA (ORCPT ); Thu, 18 Nov 2021 21:13:00 -0500 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4HwKk46rXQzbhjk; Fri, 19 Nov 2021 10:05:00 +0800 (CST) Received: from kwepemm600017.china.huawei.com (7.193.23.234) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.20; Fri, 19 Nov 2021 10:09:57 +0800 Received: from [10.174.179.234] (10.174.179.234) by kwepemm600017.china.huawei.com (7.193.23.234) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.15; Fri, 19 Nov 2021 10:09:55 +0800 Subject: Re: [PATCH 03/12] riscv: switch to relative exception tables To: Jisheng Zhang , Paul Walmsley , Palmer Dabbelt , Albert Ou , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , "Song Liu" , Yonghong Song , John Fastabend , KP Singh , Masahiro Yamada , Michal Marek , "Nick Desaulniers" References: <20211118192130.48b8f04c@xhacker> <20211118192251.749c04f7@xhacker> CC: Kefeng Wang , , , , , From: tongtiangen Message-ID: Date: Fri, 19 Nov 2021 10:09:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.7.1 MIME-Version: 1.0 In-Reply-To: <20211118192251.749c04f7@xhacker> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.179.234] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemm600017.china.huawei.com (7.193.23.234) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi jisheng: eBPF's exception tables needs to be modified to relative synchronously. I modified and verified the code as follows: =================== --- a/arch/riscv/net/bpf_jit_comp64.c +++ b/arch/riscv/net/bpf_jit_comp64.c @@ -499,7 +499,7 @@ static int add_exception_handler(const struct bpf_insn *insn, offset = pc - (long)&ex->insn; if (WARN_ON_ONCE(offset >= 0 || offset < INT_MIN)) return -ERANGE; - ex->insn = pc; + ex->insn = offset; =================== Thanks. Reviewed-by:Tong Tiangen On 2021/11/18 19:22, Jisheng Zhang wrote: > From: Jisheng Zhang > > Similar as other architectures such as arm64, x86 and so on, use > offsets relative to the exception table entry values rather than > absolute addresses for both the exception locationand the fixup. > > However, RISCV label difference will actually produce two relocations, > a pair of R_RISCV_ADD32 and R_RISCV_SUB32. Take below simple code for > example: > > $ cat test.S > .section .text > 1: > nop > .section __ex_table,"a" > .balign 4 > .long (1b - .) > .previous > > $ riscv64-linux-gnu-gcc -c test.S > $ riscv64-linux-gnu-readelf -r test.o > Relocation section '.rela__ex_table' at offset 0x100 contains 2 entries: > Offset Info Type Sym. Value Sym. Name + Addend > 000000000000 000600000023 R_RISCV_ADD32 0000000000000000 .L1^B1 + 0 > 000000000000 000500000027 R_RISCV_SUB32 0000000000000000 .L0 + 0 > > The modpost will complain the R_RISCV_SUB32 relocation, so we need to > patch modpost.c to skip this relocation for .rela__ex_table section. > > After this patch, the __ex_table section size of defconfig vmlinux is > reduced from 7072 Bytes to 3536 Bytes. > > Signed-off-by: Jisheng Zhang > Reviewed-by: Kefeng Wang > --- > arch/riscv/include/asm/Kbuild | 1 - > arch/riscv/include/asm/extable.h | 25 +++++++++++++++++++++++++ > arch/riscv/include/asm/uaccess.h | 4 ++-- > arch/riscv/lib/uaccess.S | 4 ++-- > arch/riscv/mm/extable.c | 2 +- > scripts/mod/modpost.c | 15 +++++++++++++++ > scripts/sorttable.c | 2 +- > 7 files changed, 46 insertions(+), 7 deletions(-) > create mode 100644 arch/riscv/include/asm/extable.h > > diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild > index 445ccc97305a..57b86fd9916c 100644 > --- a/arch/riscv/include/asm/Kbuild > +++ b/arch/riscv/include/asm/Kbuild > @@ -1,6 +1,5 @@ > # SPDX-License-Identifier: GPL-2.0 > generic-y += early_ioremap.h > -generic-y += extable.h > generic-y += flat.h > generic-y += kvm_para.h > generic-y += user.h > diff --git a/arch/riscv/include/asm/extable.h b/arch/riscv/include/asm/extable.h > new file mode 100644 > index 000000000000..84760392fc69 > --- /dev/null > +++ b/arch/riscv/include/asm/extable.h > @@ -0,0 +1,25 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _ASM_RISCV_EXTABLE_H > +#define _ASM_RISCV_EXTABLE_H > + > +/* > + * The exception table consists of pairs of relative offsets: the first > + * is the relative offset to an instruction that is allowed to fault, > + * and the second is the relative offset at which the program should > + * continue. No registers are modified, so it is entirely up to the > + * continuation code to figure out what to do. > + * > + * All the routines below use bits of fixup code that are out of line > + * with the main instruction path. This means when everything is well, > + * we don't even have to jump over them. Further, they do not intrude > + * on our cache or tlb entries. > + */ > + > +struct exception_table_entry { > + int insn, fixup; > +}; > + > +#define ARCH_HAS_RELATIVE_EXTABLE > + > +int fixup_exception(struct pt_regs *regs); > +#endif > diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h > index 714cd311d9f1..0f2c5b9d2e8f 100644 > --- a/arch/riscv/include/asm/uaccess.h > +++ b/arch/riscv/include/asm/uaccess.h > @@ -12,8 +12,8 @@ > > #define _ASM_EXTABLE(from, to) \ > " .pushsection __ex_table, \"a\"\n" \ > - " .balign " RISCV_SZPTR " \n" \ > - " " RISCV_PTR "(" #from "), (" #to ")\n" \ > + " .balign 4\n" \ > + " .long (" #from " - .), (" #to " - .)\n" \ > " .popsection\n" > > /* > diff --git a/arch/riscv/lib/uaccess.S b/arch/riscv/lib/uaccess.S > index 63bc691cff91..55f80f84e23f 100644 > --- a/arch/riscv/lib/uaccess.S > +++ b/arch/riscv/lib/uaccess.S > @@ -7,8 +7,8 @@ > 100: > \op \reg, \addr > .section __ex_table,"a" > - .balign RISCV_SZPTR > - RISCV_PTR 100b, \lbl > + .balign 4 > + .long (100b - .), (\lbl - .) > .previous > .endm > > diff --git a/arch/riscv/mm/extable.c b/arch/riscv/mm/extable.c > index ddb7d3b99e89..d8d239c2c1bd 100644 > --- a/arch/riscv/mm/extable.c > +++ b/arch/riscv/mm/extable.c > @@ -28,6 +28,6 @@ int fixup_exception(struct pt_regs *regs) > return rv_bpf_fixup_exception(fixup, regs); > #endif > > - regs->epc = fixup->fixup; > + regs->epc = (unsigned long)&fixup->fixup + fixup->fixup; > return 1; > } > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c > index cb8ab7d91d30..6bfa33217914 100644 > --- a/scripts/mod/modpost.c > +++ b/scripts/mod/modpost.c > @@ -1830,6 +1830,14 @@ static int addend_mips_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r) > return 0; > } > > +#ifndef EM_RISCV > +#define EM_RISCV 243 > +#endif > + > +#ifndef R_RISCV_SUB32 > +#define R_RISCV_SUB32 39 > +#endif > + > static void section_rela(const char *modname, struct elf_info *elf, > Elf_Shdr *sechdr) > { > @@ -1866,6 +1874,13 @@ static void section_rela(const char *modname, struct elf_info *elf, > r_sym = ELF_R_SYM(r.r_info); > #endif > r.r_addend = TO_NATIVE(rela->r_addend); > + switch (elf->hdr->e_machine) { > + case EM_RISCV: > + if (!strcmp("__ex_table", fromsec) && > + ELF_R_TYPE(r.r_info) == R_RISCV_SUB32) > + continue; > + break; > + } > sym = elf->symtab_start + r_sym; > /* Skip special sections */ > if (is_shndx_special(sym->st_shndx)) > diff --git a/scripts/sorttable.c b/scripts/sorttable.c > index b7c2ad71f9cf..0c031e47a419 100644 > --- a/scripts/sorttable.c > +++ b/scripts/sorttable.c > @@ -376,6 +376,7 @@ static int do_file(char const *const fname, void *addr) > case EM_PARISC: > case EM_PPC: > case EM_PPC64: > + case EM_RISCV: > custom_sort = sort_relative_table; > break; > case EM_ARCOMPACT: > @@ -383,7 +384,6 @@ static int do_file(char const *const fname, void *addr) > case EM_ARM: > case EM_MICROBLAZE: > case EM_MIPS: > - case EM_RISCV: > case EM_XTENSA: > break; > default: >