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modpost: fix section_mismatch message for R_ARM_THM_{CALL,JUMP24,JUMP19}

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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: c9698e5cd6 ("ARM: 7964/1: Detect section mismatches in thumb relocations")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Masahiro Yamada 2023-06-01 21:10:00 +09:00
parent cd1824fb7a
commit 3310bae805
1 changed files with 47 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

53
scripts/mod/modpost.c
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@ -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;