Commit 2f2f7e47 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

objtool: Add elf_create_undef_symbol() 



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

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarMiroslav Benes <mbenes@suse.cz>
Link: https://lkml.kernel.org/r/20210326151300.064743095@infradead.org
parent 9a7827b7

tools/objtool/elf.c

+60 −0
Original line number Diff line number Diff line
@@ -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)

{

tools/objtool/include/objtool/elf.h

+1 −0
Original line number Diff line number Diff line
@@ -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);