LoongArch: Switch to relative exception tables

Similar to other architectures such as arm64, x86, riscv and so on, use offsets relative to the exception table entry values rather than their absolute addresses for both the exception location and the fixup. However, LoongArch label difference because it will actually produce two relocations, a pair of R_LARCH_ADD32 and R_LARCH_SUB32. Take simple code below for example: $ cat test_ex_table.S .section .text 1: nop .section __ex_table,"a" .balign 4 .long (1b - .) .previous $ loongarch64-unknown-linux-gnu-gcc -c test_ex_table.S $ loongarch64-unknown-linux-gnu-readelf -Wr test_ex_table.o Relocation section '.rela__ex_table' at offset 0x100 contains 2 entries: Offset Info Type Symbol's Value Symbol's Name + Addend 0000000000000000 0000000600000032 R_LARCH_ADD32 0000000000000000 .L1^B1 + 0 0000000000000000 0000000500000037 R_LARCH_SUB32 0000000000000000 L0^A + 0 The modpost will complain the R_LARCH_SUB32 relocation, so we need to patch modpost.c to skip this relocation for .rela__ex_table section.

Youling Tang committed 3 years ago

Commit 3d36f421 parent 508f28c6 files · +69 −18Browse files

Unified · Split

6 files

arch/loongarch/include/asm/asm-extable.h +6 −6
arch/loongarch/include/asm/extable.h +26 −0
arch/loongarch/include/asm/uaccess.h +1 −1
arch/loongarch/mm/extable.c +22 −10
scripts/mod/modpost.c +13 −0
scripts/sorttable.c +1 −1

arch/loongarch/include/asm/asm-extable.h+6−6

@@ -6,9 +6,9 @@ · 5 unmodified lines
6	6
7	7	#define __ASM_EXTABLE_RAW(insn, fixup) \
8	8	.pushsection __ex_table, "a"; \
9		− .balign 8; \
10		− .quad (insn); \
11		− .quad (fixup); \
	9	+ .balign 4; \
	10	+ .long ((insn) - .); \
	11	+ .long ((fixup) - .); \
12	12	.popsection;
13	13
14	14	.macro _asm_extable, insn, fixup
@@ -22,9 +22,9 @@ · 7 unmodified lines
22	22
23	23	#define __ASM_EXTABLE_RAW(insn, fixup) \
24	24	".pushsection __ex_table, \"a\"\n" \
25		− ".balign 8\n" \
26		− ".quad ((" insn "))\n" \
27		− ".quad ((" fixup "))\n" \
	25	+ ".balign 4\n" \
	26	+ ".long ((" insn ") - .)\n" \
	27	+ ".long ((" fixup ") - .)\n" \
28	28	".popsection\n"
29	29
30	30	#define _ASM_EXTABLE(insn, fixup) \

arch/loongarch/include/asm/extable.h+26−0

@@ -0,0 +1,26 @@
	1	+/* SPDX-License-Identifier: GPL-2.0 */
	2	+#ifndef _ASM_LOONGARCH_EXTABLE_H
	3	+#define _ASM_LOONGARCH_EXTABLE_H
	4	+
	5	+/*
	6	+ * The exception table consists of pairs of relative offsets: the first
	7	+ * is the relative offset to an instruction that is allowed to fault,
	8	+ * and the second is the relative offset at which the program should
	9	+ * continue. No registers are modified, so it is entirely up to the
	10	+ * continuation code to figure out what to do.
	11	+ *
	12	+ * All the routines below use bits of fixup code that are out of line
	13	+ * with the main instruction path. This means when everything is well,
	14	+ * we don't even have to jump over them. Further, they do not intrude
	15	+ * on our cache or tlb entries.
	16	+ */
	17	+
	18	+struct exception_table_entry {
	19	+ int insn, fixup;
	20	+};
	21	+
	22	+#define ARCH_HAS_RELATIVE_EXTABLE
	23	+
	24	+bool fixup_exception(struct pt_regs *regs);
	25	+
	26	+#endif

arch/loongarch/include/asm/uaccess.h+1−1

@@ -15,8 +15,8 @@ · 14 unmodified lines
15	15	#include <linux/string.h>
16	16	#include <linux/extable.h>
17	17	#include <asm/pgtable.h>
	18	+#include <asm/extable.h>
18	19	#include <asm/asm-extable.h>
19		−#include <asm-generic/extable.h>
20	20	#include <asm-generic/access_ok.h>
21	21
22	22	extern u64 __ua_limit;

arch/loongarch/mm/extable.c+22−10

@@ -3,20 +3,32 @@ · 2 unmodified lines
3	3	* Copyright (C) 2020-2022 Loongson Technology Corporation Limited
4	4	*/
5	5	#include <linux/extable.h>
6		−#include <linux/spinlock.h>
7		−#include <asm/branch.h>
8	6	#include <linux/uaccess.h>
	7	+#include <asm/asm-extable.h>
	8	+#include <asm/branch.h>
	9	+
	10	+static inline unsigned long
	11	+get_ex_fixup(const struct exception_table_entry *ex)
	12	+{
	13	+ return ((unsigned long)&ex->fixup + ex->fixup);
	14	+}
9	15
10		−int fixup_exception(struct pt_regs *regs)
	16	+static bool ex_handler_fixup(const struct exception_table_entry *ex,
	17	+ struct pt_regs *regs)
11	18	{
12		− const struct exception_table_entry *fixup;
	19	+ regs->csr_era = get_ex_fixup(ex);
13	20
14		− fixup = search_exception_tables(exception_era(regs));
15		− if (fixup) {
16		− regs->csr_era = fixup->fixup;
	21	+ return true;
	22	+}
	23	+
	24	+
	25	+bool fixup_exception(struct pt_regs *regs)
	26	+{
	27	+ const struct exception_table_entry *ex;
17	28
18		− return 1;
19		− }
	29	+ ex = search_exception_tables(exception_era(regs));
	30	+ if (!ex)
	31	+ return false;
20	32
21		− return 0;
	33	+ return ex_handler_fixup(ex, regs);
22	34	}

scripts/mod/modpost.c+13−0

@@ -1523,6 +1523,14 @@ static int addend_mips_rel(struct elf_info elf, Elf_Shdr sechdr, Elf_Rela *r) · 1522 unmodified lines
1523	1523	#define R_RISCV_SUB32 39
1524	1524	#endif
1525	1525
	1526	+#ifndef EM_LOONGARCH
	1527	+#define EM_LOONGARCH 258
	1528	+#endif
	1529	+
	1530	+#ifndef R_LARCH_SUB32
	1531	+#define R_LARCH_SUB32 55
	1532	+#endif
	1533	+
1526	1534	static void section_rela(const char modname, struct elf_info elf,
1527	1535	Elf_Shdr *sechdr)
1528	1536	{
@@ -1564,6 +1572,11 @@ static void section_rela(const char modname, struct elf_info elf, · 35 unmodified lines
1564	1572	ELF_R_TYPE(r.r_info) == R_RISCV_SUB32)
1565	1573	continue;
1566	1574	break;
	1575	+ case EM_LOONGARCH:
	1576	+ if (!strcmp("__ex_table", fromsec) &&
	1577	+ ELF_R_TYPE(r.r_info) == R_LARCH_SUB32)
	1578	+ continue;
	1579	+ break;
1567	1580	}
1568	1581	sym = elf->symtab_start + r_sym;
1569	1582	/* Skip special sections */

scripts/sorttable.c+1−1

@@ -312,12 +312,12 @@ static int do_file(char const const fname, void addr) · 311 unmodified lines
312	312	case EM_PARISC:
313	313	case EM_PPC:
314	314	case EM_PPC64:
	315	+ case EM_LOONGARCH:
315	316	custom_sort = sort_relative_table;
316	317	break;
317	318	case EM_ARCOMPACT:
318	319	case EM_ARCV2:
319	320	case EM_ARM:
320		− case EM_LOONGARCH:
321	321	case EM_MICROBLAZE:
322	322	case EM_MIPS:
323	323	case EM_XTENSA: