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objtool: Fix .symtab_shndx handling for elf_create_undef_symbol()

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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: 2f2f7e47f0 ("objtool: Add elf_create_undef_symbol()")
Reported-by: Nick Desaulniers <ndesaulniers@google.com>
Suggested-by: Fangrui Song <maskray@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lkml.kernel.org/r/YL3q1qFO9QIRL/BA@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2021-06-07 11:45:58 +02:00
parent 614124bea7
commit 584fd3b318
1 changed files with 24 additions and 1 deletions
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25
tools/objtool/elf.c
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@ -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);