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Commit ad3c4ecf authored by Masahiro Yamada's avatar Masahiro Yamada Committed by Greg Kroah-Hartman
Browse files

modpost: fix section mismatch message for R_ARM_{PC24,CALL,JUMP24} 

[ Upstream commit 56a24b8ce6a7f9c4a21b2276a8644f6f3d8fc14d ]

addend_arm_rel() processes R_ARM_PC24, R_ARM_CALL, R_ARM_JUMP24 in a
wrong way.

Here, test code.

[test code for R_ARM_JUMP24]

  .section .init.text,"ax"
  bar:
          bx      lr

  .section .text,"ax"
  .globl foo
  foo:
          b       bar

[test code for R_ARM_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 ARM multi_v7_defconfig, 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 imported (with adjustment) sign_extend32() from include/linux/bitops.h.

The '+8' 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: 56a974fa ("kbuild: make better section mismatch reports on arm")
Fixes: 6e2e340b ("ARM: 7324/1: modpost: Fix section warnings for ARM for many compilers")
Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 084bf580

scripts/mod/modpost.c

+12 −0
Original line number Diff line number Diff line
@@ -1812,12 +1812,20 @@ static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r) 
#define	R_ARM_THM_JUMP19	51

#endif



static int32_t sign_extend32(int32_t value, int index)

{

	uint8_t shift = 31 - index;



	return (int32_t)(value << shift) >> shift;

}



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;

	int32_t offset;



	switch (r_typ) {

	case R_ARM_ABS32:
@@ -1827,6 +1835,10 @@ static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r) 
	case R_ARM_PC24:

	case R_ARM_CALL:

	case R_ARM_JUMP24:

		inst = TO_NATIVE(*(uint32_t *)loc);

		offset = sign_extend32((inst & 0x00ffffff) << 2, 25);

		r->r_addend = offset + sym->st_value + 8;

		break;

	case R_ARM_THM_CALL:

	case R_ARM_THM_JUMP24:

	case R_ARM_THM_JUMP19: