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LoongArch: Switch to relative exception tables

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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.

Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
This commit is contained in:
Youling Tang 2022-12-10 22:39:48 +08:00 • committed by Huacai Chen
parent 508f28c671
commit 3d36f4298b
6 changed files with 72 additions and 21 deletions
Download patch file Download diff file Expand all files Collapse all files

13
scripts/mod/modpost.c
View file

@ -1523,6 +1523,14 @@ static int addend_mips_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
#define R_RISCV_SUB32 39
#endif
#ifndef EM_LOONGARCH
#define EM_LOONGARCH 258
#endif
#ifndef R_LARCH_SUB32
#define R_LARCH_SUB32 55
#endif
static void section_rela(const char *modname, struct elf_info *elf,
Elf_Shdr *sechdr)
{
@ -1564,6 +1572,11 @@ static void section_rela(const char *modname, struct elf_info *elf,
ELF_R_TYPE(r.r_info) == R_RISCV_SUB32)
continue;
break;
case EM_LOONGARCH:
if (!strcmp("__ex_table", fromsec) &&
ELF_R_TYPE(r.r_info) == R_LARCH_SUB32)
continue;
break;
}
sym = elf->symtab_start + r_sym;
/* Skip special sections */

2
scripts/sorttable.c
View file

@ -312,12 +312,12 @@ static int do_file(char const *const fname, void *addr)
case EM_PARISC:
case EM_PPC:
case EM_PPC64:
case EM_LOONGARCH:
custom_sort = sort_relative_table;
break;
case EM_ARCOMPACT:
case EM_ARCV2:
case EM_ARM:
case EM_LOONGARCH:
case EM_MICROBLAZE:
case EM_MIPS:
case EM_XTENSA: