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objtool: Handle PC relative relocation type

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For the most part, an absolute relocation type is used for rodata.
In the case of STT_SECTION, reloc->sym->offset is always zero, for
the other symbol types, reloc_addend(reloc) is always zero, thus it
can use a simple statement "reloc->sym->offset + reloc_addend(reloc)"
to obtain the symbol offset for various symbol types.

When compiling on LoongArch, there exist PC relative relocation types
for rodata, it needs to calculate the symbol offset with "S + A - PC"
according to the spec of "ELF for the LoongArch Architecture".

If there is only one jump table in the rodata, the "PC" is the entry
address which is equal with the value of reloc_offset(reloc), at this
time, reloc_offset(table) is 0.

If there are many jump tables in the rodata, the "PC" is the offset
of the jump table's base address which is equal with the value of
reloc_offset(reloc) - reloc_offset(table).

So for LoongArch, if the relocation type is PC relative, it can use a
statement "reloc_offset(reloc) - reloc_offset(table)" to get the "PC"
value when calculating the symbol offset with "S + A - PC" for one or
many jump tables in the rodata.

Add an arch-specific function arch_jump_table_sym_offset() to assign
the symbol offset, for the most part that is an absolute relocation,
the default value is "reloc->sym->offset + reloc_addend(reloc)" in
the weak definition, it can be overridden by each architecture that
has different requirements.

Link: https://github.com/loongson/la-abi-specs/blob/release/laelf.adoc
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Link: https://lore.kernel.org/r/20250211115016.26913-4-yangtiezhu@loongson.cn
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
This commit is contained in:
Tiezhu Yang 2025-02-11 19:50:12 +08:00 • committed by Josh Poimboeuf
parent 091bf313f8
commit c4b93b0623
4 changed files with 27 additions and 5 deletions
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17
tools/objtool/arch/loongarch/decode.c
View file

@ -5,10 +5,7 @@
#include <asm/inst.h>
#include <asm/orc_types.h>
#include <linux/objtool_types.h>
#ifndef EM_LOONGARCH
#define EM_LOONGARCH 258
#endif
#include <arch/elf.h>
int arch_ftrace_match(char *name)
{
@ -374,3 +371,15 @@ unsigned int arch_reloc_size(struct reloc *reloc)
return 8;
}
}
unsigned long arch_jump_table_sym_offset(struct reloc *reloc, struct reloc *table)
{
switch (reloc_type(reloc)) {
case R_LARCH_32_PCREL:
case R_LARCH_64_PCREL:
return reloc->sym->offset + reloc_addend(reloc) -
(reloc_offset(reloc) - reloc_offset(table));
default:
return reloc->sym->offset + reloc_addend(reloc);
}
}

7
tools/objtool/arch/loongarch/include/arch/elf.h
View file

@ -18,6 +18,13 @@
#ifndef R_LARCH_32_PCREL
#define R_LARCH_32_PCREL 99
#endif
#ifndef R_LARCH_64_PCREL
#define R_LARCH_64_PCREL 109
#endif
#ifndef EM_LOONGARCH
#define EM_LOONGARCH 258
#endif
#define R_NONE R_LARCH_NONE
#define R_ABS32 R_LARCH_32

7
tools/objtool/check.c
View file

@ -1944,6 +1944,11 @@ out:
return ret;
}
__weak unsigned long arch_jump_table_sym_offset(struct reloc *reloc, struct reloc *table)
{
return reloc->sym->offset + reloc_addend(reloc);
}
static int add_jump_table(struct objtool_file *file, struct instruction *insn,
struct reloc *next_table)
{
@ -1972,7 +1977,7 @@ static int add_jump_table(struct objtool_file *file, struct instruction *insn,
if (prev_offset && reloc_offset(reloc) != prev_offset + arch_reloc_size(reloc))
break;
sym_offset = reloc->sym->offset + reloc_addend(reloc);
sym_offset = arch_jump_table_sym_offset(reloc, table);
/* Detect function pointers from contiguous objects: */
if (reloc->sym->sec == pfunc->sec && sym_offset == pfunc->offset)

1
tools/objtool/include/objtool/arch.h
View file

@ -98,5 +98,6 @@ int arch_rewrite_retpolines(struct objtool_file *file);
bool arch_pc_relative_reloc(struct reloc *reloc);
unsigned int arch_reloc_size(struct reloc *reloc);
unsigned long arch_jump_table_sym_offset(struct reloc *reloc, struct reloc *table);
#endif /* _ARCH_H */