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authorMasahiro Yamada <masahiroy@kernel.org>2023-06-01 21:09:59 +0900
committerMasahiro Yamada <masahiroy@kernel.org>2023-06-04 01:36:27 +0900
commitcd1824fb7a377882497e8b87a6f3a9ec19be3623 (patch)
tree3f54d8c64af7ebcaaddfdb1e4a5bfdd6fb5bc62f /scripts
parentb1a9651d48b42f3eddf095123c09f93e4df23060 (diff)
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modpost: detect section mismatch for R_ARM_THM_{MOVW_ABS_NC,MOVT_ABS}
When CONFIG_THUMB2_KERNEL is enabled, modpost fails to detect some types of section mismatches. [test code] #include <linux/init.h> int __initdata foo; int get_foo(void) { return foo; } It is apparently a bad reference, but modpost does not report anything. The test code above produces the following relocations. Relocation section '.rel.text' at offset 0x1e8 contains 2 entries: Offset Info Type Sym.Value Sym. Name 00000000 0000052f R_ARM_THM_MOVW_AB 00000000 .LANCHOR0 00000004 00000530 R_ARM_THM_MOVT_AB 00000000 .LANCHOR0 Currently, R_ARM_THM_MOVW_ABS_NC and R_ARM_THM_MOVT_ABS are just skipped. Add code to handle them. I checked arch/arm/kernel/module.c to learn how the offset is encoded in the instruction. One more thing to note for Thumb instructions - the st_value is an odd value, so you need to mask the bit 0 to get the offset. Otherwise, you will get an off-by-one error in the nearest symbol look-up. It is documented in "ELF for the ARM Architecture" [1]: In addition to the normal rules for symbol values the following rules shall also apply to symbols of type STT_FUNC: * If the symbol addresses an Arm instruction, its value is the address of the instruction (in a relocatable object, the offset of the instruction from the start of the section containing it). * If the symbol addresses a Thumb instruction, its value is the address of the instruction with bit zero set (in a relocatable object, the section offset with bit zero set). * For the purposes of relocation the value used shall be the address of the instruction (st_value & ~1). [1]: https://github.com/ARM-software/abi-aa/blob/main/aaelf32/aaelf32.rst Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Diffstat (limited to 'scripts')
-rw-r--r--scripts/mod/modpost.c31
1 files changed, 26 insertions, 5 deletions
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 32d56efe3f3b..ec16f4d7e55a 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1082,7 +1082,8 @@ static Elf_Sym *find_nearest_sym(struct elf_info *elf, Elf_Addr addr,
{
Elf_Sym *sym;
Elf_Sym *near = NULL;
- Elf_Addr distance;
+ Elf_Addr sym_addr, distance;
+ bool is_arm = (elf->hdr->e_machine == EM_ARM);
for (sym = elf->symtab_start; sym < elf->symtab_stop; sym++) {
if (get_secindex(elf, sym) != secndx)
@@ -1090,10 +1091,19 @@ static Elf_Sym *find_nearest_sym(struct elf_info *elf, Elf_Addr addr,
if (!is_valid_name(elf, sym))
continue;
- if (addr >= sym->st_value)
- distance = addr - sym->st_value;
+ sym_addr = sym->st_value;
+
+ /*
+ * For ARM Thumb instruction, the bit 0 of st_value is set
+ * if the symbol is STT_FUNC type. Mask it to get the address.
+ */
+ if (is_arm && ELF_ST_TYPE(sym->st_info) == STT_FUNC)
+ sym_addr &= ~1;
+
+ if (addr >= sym_addr)
+ distance = addr - sym_addr;
else if (allow_negative)
- distance = sym->st_value - addr;
+ distance = sym_addr - addr;
else
continue;
@@ -1266,7 +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;
+ uint32_t inst, upper, lower;
int32_t offset;
switch (r_typ) {
@@ -1288,6 +1298,17 @@ static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
offset = sign_extend32((inst & 0x00ffffff) << 2, 25);
r->r_addend = offset + sym->st_value + 8;
break;
+ case R_ARM_THM_MOVW_ABS_NC:
+ case R_ARM_THM_MOVT_ABS:
+ upper = TO_NATIVE(*(uint16_t *)loc);
+ lower = TO_NATIVE(*((uint16_t *)loc + 1));
+ offset = sign_extend32(((upper & 0x000f) << 12) |
+ ((upper & 0x0400) << 1) |
+ ((lower & 0x7000) >> 4) |
+ (lower & 0x00ff),
+ 15);
+ r->r_addend = offset + sym->st_value;
+ break;
case R_ARM_THM_CALL:
case R_ARM_THM_JUMP24:
case R_ARM_THM_JUMP19: