All of lore.kernel.org
 help / color / mirror / Atom feed
From: Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
To: "Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Michal Marek" <michal.lkml@markovi.net>,
	"Nick Desaulniers" <ndesaulniers@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>,
	Tong Tiangen <tongtiangen@huawei.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	linux-kbuild@vger.kernel.org
Subject: [PATCH 03/12] riscv: switch to relative exception tables
Date: Thu, 18 Nov 2021 19:22:51 +0800	[thread overview]
Message-ID: <20211118192251.749c04f7@xhacker> (raw)
In-Reply-To: <20211118192130.48b8f04c@xhacker>

From: Jisheng Zhang <jszhang@kernel.org>

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 <jszhang@kernel.org>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 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:
-- 
2.33.0



_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID
From: Jisheng Zhang <jszhang3@mail.ustc.edu.cn>
To: "Paul Walmsley" <paul.walmsley@sifive.com>,
	"Palmer Dabbelt" <palmer@dabbelt.com>,
	"Albert Ou" <aou@eecs.berkeley.edu>,
	"Björn Töpel" <bjorn@kernel.org>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Andrii Nakryiko" <andrii@kernel.org>,
	"Martin KaFai Lau" <kafai@fb.com>,
	"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	"KP Singh" <kpsingh@kernel.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Michal Marek" <michal.lkml@markovi.net>,
	"Nick Desaulniers" <ndesaulniers@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>,
	Tong Tiangen <tongtiangen@huawei.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, bpf@vger.kernel.org,
	linux-kbuild@vger.kernel.org
Subject: [PATCH 03/12] riscv: switch to relative exception tables
Date: Thu, 18 Nov 2021 19:22:51 +0800	[thread overview]
Message-ID: <20211118192251.749c04f7@xhacker> (raw)
In-Reply-To: <20211118192130.48b8f04c@xhacker>

From: Jisheng Zhang <jszhang@kernel.org>

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 <jszhang@kernel.org>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
---
 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:
-- 
2.33.0



  parent reply	other threads:[~2021-11-18 11:35 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-18 11:21 [PATCH v4 0/12] riscv: switch to relative extable and other improvements Jisheng Zhang
2021-11-18 11:21 ` Jisheng Zhang
2021-11-18 11:22 ` [PATCH 01/12] riscv: remove unused __cmpxchg_user() macro Jisheng Zhang
2021-11-18 11:22   ` Jisheng Zhang
2021-11-18 11:22 ` [PATCH 02/12] riscv: consolidate __ex_table construction Jisheng Zhang
2021-11-18 11:22   ` Jisheng Zhang
2021-11-18 11:22 ` Jisheng Zhang [this message]
2021-11-18 11:22   ` [PATCH 03/12] riscv: switch to relative exception tables Jisheng Zhang
2021-11-19  2:09   ` tongtiangen
2021-11-19  2:09     ` tongtiangen
2021-11-18 11:23 ` [PATCH 04/12] riscv: bpf: move rv_bpf_fixup_exception signature to extable.h Jisheng Zhang
2021-11-18 11:23   ` Jisheng Zhang
2021-11-18 11:24 ` [PATCH 05/12] riscv: extable: make fixup_exception() return bool Jisheng Zhang
2021-11-18 11:24   ` Jisheng Zhang
2021-11-18 11:24 ` [PATCH 06/12] riscv: extable: use `ex` for `exception_table_entry` Jisheng Zhang
2021-11-18 11:24   ` Jisheng Zhang
2021-11-18 11:25 ` [PATCH 07/12] riscv: lib: uaccess: fold fixups into body Jisheng Zhang
2021-11-18 11:25   ` Jisheng Zhang
2021-11-18 11:25 ` [PATCH 08/12] riscv: extable: consolidate definitions Jisheng Zhang
2021-11-18 11:25   ` Jisheng Zhang
2021-11-18 11:26 ` [PATCH 09/12] riscv: extable: add `type` and `data` fields Jisheng Zhang
2021-11-18 11:26   ` Jisheng Zhang
2021-11-18 11:42   ` Jisheng Zhang
2021-11-18 11:42     ` Jisheng Zhang
2021-11-18 15:21     ` Mark Rutland
2021-11-18 15:21       ` Mark Rutland
2022-01-06  3:21       ` Palmer Dabbelt
2022-01-06  3:21         ` Palmer Dabbelt
2022-01-06 10:23         ` Mark Rutland
2022-01-06 10:23           ` Mark Rutland
2021-11-19  2:35   ` tongtiangen
2021-11-19  2:35     ` tongtiangen
2021-11-18 11:26 ` [PATCH 10/12] riscv: add gpr-num.h Jisheng Zhang
2021-11-18 11:26   ` Jisheng Zhang
2021-11-18 11:26 ` [PATCH 11/12] riscv: extable: add a dedicated uaccess handler Jisheng Zhang
2021-11-18 11:26   ` Jisheng Zhang
2022-01-20 18:15   ` Mayuresh Chitale
2022-01-20 18:15     ` Mayuresh Chitale
2022-01-21 12:16     ` Jisheng Zhang
2022-01-21 12:16       ` Jisheng Zhang
2022-01-23  9:12       ` Jisheng Zhang
2022-01-23  9:12         ` Jisheng Zhang
2022-01-24 17:02         ` Mayuresh Chitale
2022-01-24 17:02           ` Mayuresh Chitale
2021-11-18 11:27 ` [PATCH 12/12] riscv: vmlinux.lds.S|vmlinux-xip.lds.S: remove `.fixup` section Jisheng Zhang
2021-11-18 11:27   ` Jisheng Zhang

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20211118192251.749c04f7@xhacker \
    --to=jszhang3@mail.ustc.edu.cn \
    --cc=andrii@kernel.org \
    --cc=aou@eecs.berkeley.edu \
    --cc=ast@kernel.org \
    --cc=bjorn@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=john.fastabend@gmail.com \
    --cc=kafai@fb.com \
    --cc=kpsingh@kernel.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-riscv@lists.infradead.org \
    --cc=masahiroy@kernel.org \
    --cc=michal.lkml@markovi.net \
    --cc=ndesaulniers@google.com \
    --cc=netdev@vger.kernel.org \
    --cc=palmer@dabbelt.com \
    --cc=paul.walmsley@sifive.com \
    --cc=songliubraving@fb.com \
    --cc=tongtiangen@huawei.com \
    --cc=wangkefeng.wang@huawei.com \
    --cc=yhs@fb.com \
    --subject='Re: [PATCH 03/12] riscv: switch to relative exception tables' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.