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objtool: Provide elf_write_{insn,reloc}()

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This provides infrastructure to rewrite instructions; this is
immediately useful for helping out with KCOV-vs-noinstr, but will
also come in handy for a bunch of variable sized jump-label patches
that are still on ice.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This commit is contained in:
Peter Zijlstra 2020-06-12 15:43:00 +02:00
parent 2b10be23ac
commit fdabdd0b05
2 changed files with 45 additions and 2 deletions
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40
tools/objtool/elf.c
View File

@ -529,8 +529,9 @@ static int read_relas(struct elf *elf)
rela->addend = rela->rela.r_addend;
rela->offset = rela->rela.r_offset;
symndx = GELF_R_SYM(rela->rela.r_info);
rela->sym = find_symbol_by_index(elf, symndx);
rela->sec = sec;
rela->idx = i;
rela->sym = find_symbol_by_index(elf, symndx);
if (!rela->sym) {
WARN("can't find rela entry symbol %d for %s",
symndx, sec->name);
@ -784,6 +785,43 @@ int elf_rebuild_rela_section(struct elf *elf, struct section *sec)
return 0;
}
int elf_write_insn(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len,
const char *insn)
{
Elf_Data *data = sec->data;
if (data->d_type != ELF_T_BYTE || data->d_off) {
WARN("write to unexpected data for section: %s", sec->name);
return -1;
}
memcpy(data->d_buf + offset, insn, len);
elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY);
elf->changed = true;
return 0;
}
int elf_write_rela(struct elf *elf, struct rela *rela)
{
struct section *sec = rela->sec;
rela->rela.r_info = GELF_R_INFO(rela->sym->idx, rela->type);
rela->rela.r_addend = rela->addend;
rela->rela.r_offset = rela->offset;
if (!gelf_update_rela(sec->data, rela->idx, &rela->rela)) {
WARN_ELF("gelf_update_rela");
return -1;
}
elf->changed = true;
return 0;
}
int elf_write(struct elf *elf)
{
struct section *sec;

7
tools/objtool/elf.h
View File

@ -64,9 +64,10 @@ struct rela {
GElf_Rela rela;
struct section *sec;
struct symbol *sym;
unsigned int type;
unsigned long offset;
unsigned int type;
int addend;
int idx;
bool jump_table_start;
};
@ -119,6 +120,10 @@ struct elf *elf_open_read(const char *name, int flags);
struct section *elf_create_section(struct elf *elf, const char *name, size_t entsize, int nr);
struct section *elf_create_rela_section(struct elf *elf, struct section *base);
void elf_add_rela(struct elf *elf, struct rela *rela);
int elf_write_insn(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len,
const char *insn);
int elf_write_rela(struct elf *elf, struct rela *rela);
int elf_write(struct elf *elf);
void elf_close(struct elf *elf);