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

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@kernel.org>

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index ec16f4d7e55ae80cd5cbf3caed85a16c62da1e8b..4e911ab711d4bf2231bcb0fb37a7f428a16b5055 100644 (file)
--- 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;