addend_arm_rel() processes R_ARM_THM_CALL, R_ARM_THM_JUMP24,
R_ARM_THM_JUMP19 in a wrong way.
Here, test code.
[test code for R_ARM_THM_JUMP24]
.section .init.text,"ax"
bar:
bx lr
.section .text,"ax"
.globl foo
foo:
b bar
[test code for R_ARM_THM_CALL]
.section .init.text,"ax"
bar:
bx lr
.section .text,"ax"
.globl foo
foo:
push {lr}
bl bar
pop {pc}
If you compile it with CONFIG_THUMB2_KERNEL=y, modpost will show the
symbol name, (unknown).
WARNING: modpost: vmlinux.o: section mismatch in reference: foo (section: .text) -> (unknown) (section: .init.text)
(You need to use GNU linker instead of LLD to reproduce it.)
Fix the code to make modpost show the correct symbol name. I checked
arch/arm/kernel/module.c to learn the encoding of R_ARM_THM_CALL and
R_ARM_THM_JUMP24. The module does not support R_ARM_THM_JUMP19, but
I checked its encoding in ARM ARM.
The '+4' is the compensation for pc-relative instruction. It is
documented in "ELF for the Arm Architecture" [1].
"If the relocation is pc-relative then compensation for the PC bias
(the PC value is 8 bytes ahead of the executing instruction in Arm
state and 4 bytes in Thumb state) must be encoded in the relocation
by the object producer."
[1]: https://github.com/ARM-software/abi-aa/blob/main/aaelf32/aaelf32.rst
Fixes: c9698e5cd6ad ("ARM: 7964/1: Detect section mismatches in thumb relocations")
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---
scripts/mod/modpost.c | 53 ++++++++++++++++++++++++++++++++++++++-----
1 file changed, 47 insertions(+), 6 deletions(-)
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 528aa9175e84..55d142bb000b 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1276,7 +1276,7 @@ static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
unsigned int r_typ = ELF_R_TYPE(r->r_info);
Elf_Sym *sym = elf->symtab_start + ELF_R_SYM(r->r_info);
void *loc = reloc_location(elf, sechdr, r);
- uint32_t inst, upper, lower;
+ uint32_t inst, upper, lower, sign, j1, j2;
int32_t offset;
switch (r_typ) {
@@ -1309,13 +1309,54 @@ static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
15);
r->r_addend = offset + sym->st_value;
break;
+ case R_ARM_THM_JUMP19:
+ /*
+ * Encoding T3:
+ * S = upper[10]
+ * imm6 = upper[5:0]
+ * J1 = lower[13]
+ * J2 = lower[11]
+ * imm11 = lower[10:0]
+ * imm32 = SignExtend(S:J2:J1:imm6:imm11:'0')
+ */
+ upper = TO_NATIVE(*(uint16_t *)loc);
+ lower = TO_NATIVE(*((uint16_t *)loc + 1));
+
+ sign = (upper >> 10) & 1;
+ j1 = (lower >> 13) & 1;
+ j2 = (lower >> 11) & 1;
+ offset = sign_extend32((sign << 20) | (j2 << 19) | (j1 << 18) |
+ ((upper & 0x03f) << 12) |
+ ((lower & 0x07ff) << 1),
+ 20);
+ r->r_addend = offset + sym->st_value + 4;
+ break;
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
- case R_ARM_THM_JUMP19:
- /* From ARM ABI: ((S + A) | T) - P */
- r->r_addend = (int)(long)(elf->hdr +
- sechdr->sh_offset +
- (r->r_offset - sechdr->sh_addr));
+ /*
+ * Encoding T4:
+ * S = upper[10]
+ * imm10 = upper[9:0]
+ * J1 = lower[13]
+ * J2 = lower[11]
+ * imm11 = lower[10:0]
+ * I1 = NOT(J1 XOR S)
+ * I2 = NOT(J2 XOR S)
+ * imm32 = SignExtend(S:I1:I2:imm10:imm11:'0')
+ */
+ upper = TO_NATIVE(*(uint16_t *)loc);
+ lower = TO_NATIVE(*((uint16_t *)loc + 1));
+
+ sign = (upper >> 10) & 1;
+ j1 = (lower >> 13) & 1;
+ j2 = (lower >> 11) & 1;
+ offset = sign_extend32((sign << 24) |
+ ((~(j1 ^ sign) & 1) << 23) |
+ ((~(j2 ^ sign) & 1) << 22) |
+ ((upper & 0x03ff) << 12) |
+ ((lower & 0x07ff) << 1),
+ 24);
+ r->r_addend = offset + sym->st_value + 4;
break;
default:
return 1;
--
2.39.2
