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objtool: Add elf_create_undef_symbol()

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Allow objtool to create undefined symbols; this allows creating
relocations to symbols not currently in the symbol table.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151300.064743095@infradead.org
This commit is contained in:
Peter Zijlstra 2021-03-26 16:12:11 +01:00 committed by Ingo Molnar
parent 9a7827b778
commit 2f2f7e47f0
2 changed files with 61 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

60
tools/objtool/elf.c
View file

@ -715,6 +715,66 @@ static int elf_add_string(struct elf *elf, struct section *strtab, char *str)
return len;
}
struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)
{
struct section *symtab;
struct symbol *sym;
Elf_Data *data;
Elf_Scn *s;
sym = malloc(sizeof(*sym));
if (!sym) {
perror("malloc");
return NULL;
}
memset(sym, 0, sizeof(*sym));
sym->name = strdup(name);
sym->sym.st_name = elf_add_string(elf, NULL, sym->name);
if (sym->sym.st_name == -1)
return NULL;
sym->sym.st_info = GELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
// st_other 0
// st_shndx 0
// st_value 0
// st_size 0
symtab = find_section_by_name(elf, ".symtab");
if (!symtab) {
WARN("can't find .symtab");
return NULL;
}
s = elf_getscn(elf->elf, symtab->idx);
if (!s) {
WARN_ELF("elf_getscn");
return NULL;
}
data = elf_newdata(s);
if (!data) {
WARN_ELF("elf_newdata");
return NULL;
}
data->d_buf = &sym->sym;
data->d_size = sizeof(sym->sym);
data->d_align = 1;
sym->idx = symtab->len / sizeof(sym->sym);
symtab->len += data->d_size;
symtab->changed = true;
sym->sec = find_section_by_index(elf, 0);
elf_add_symbol(elf, sym);
return sym;
}
struct section *elf_create_section(struct elf *elf, const char *name,
unsigned int sh_flags, size_t entsize, int nr)
{

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

@ -133,6 +133,7 @@ int elf_write_insn(struct elf *elf, struct section *sec,
unsigned long offset, unsigned int len,
const char *insn);
int elf_write_reloc(struct elf *elf, struct reloc *reloc);
struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name);
int elf_write(struct elf *elf);
void elf_close(struct elf *elf);