On 2021/10/20 22:07, Jisheng Zhang wrote:
From: Jisheng Zhang <jszhang@xxxxxxxxxx>
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@xxxxxxxxxx>
---
...
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index cb8ab7d91d30..0aa14b5bd124 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1830,6 +1830,27 @@ 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 int addend_riscv_rela(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
+{
+ unsigned int r_typ = ELF_R_TYPE(r->r_info);
+ const char *fromsec;
+
+ fromsec = sech_name(elf, sechdr);
+ fromsec += strlen(".rela");
+
+ if (!strcmp("__ex_table", fromsec) && r_typ == R_RISCV_SUB32)
+ return 1; /* skip this */
+ return 0;
+}
+
static void section_rela(const char *modname, struct elf_info *elf,
Elf_Shdr *sechdr)
{
@@ -1866,6 +1887,12 @@ 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 (addend_riscv_rela(elf, sechdr, &r))
directly use
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 6ee4fa882919..39e86e4acea3 100644
--- a/scripts/sorttable.c
+++ b/scripts/sorttable.c
@@ -346,6 +346,7 @@ 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:
@@ -353,7 +354,6 @@ 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:
