Commit 584fd3b3 authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

objtool: Fix .symtab_shndx handling for elf_create_undef_symbol() 



When an ELF object uses extended symbol section indexes (IOW it has a
.symtab_shndx section), these must be kept in sync with the regular
symbol table (.symtab).

So for every new symbol we emit, make sure to also emit a
.symtab_shndx value to keep the arrays of equal size.

Note: since we're writing an UNDEF symbol, most GElf_Sym fields will
be 0 and we can repurpose one (st_size) to host the 0 for the xshndx
value.

Fixes: 2f2f7e47 ("objtool: Add elf_create_undef_symbol()")
Reported-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Suggested-by: default avatarFangrui Song <maskray@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/YL3q1qFO9QIRL/BA@hirez.programming.kicks-ass.net
parent 614124be

tools/objtool/elf.c

+24 −1
Original line number Diff line number Diff line
@@ -717,7 +717,7 @@ static int elf_add_string(struct elf *elf, struct section *strtab, char *str) 


struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name)

{

	struct section *symtab;

	struct section *symtab, *symtab_shndx;

	struct symbol *sym;

	Elf_Data *data;

	Elf_Scn *s;
@@ -769,6 +769,29 @@ struct symbol *elf_create_undef_symbol(struct elf *elf, const char *name) 
	symtab->len += data->d_size;

	symtab->changed = true;



	symtab_shndx = find_section_by_name(elf, ".symtab_shndx");

	if (symtab_shndx) {

		s = elf_getscn(elf->elf, symtab_shndx->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.st_size; /* conveniently 0 */

		data->d_size = sizeof(Elf32_Word);

		data->d_align = 4;

		data->d_type = ELF_T_WORD;



		symtab_shndx->len += 4;

		symtab_shndx->changed = true;

	}



	sym->sec = find_section_by_index(elf, 0);



	elf_add_symbol(elf, sym);