On Thu, 14 Jan 2021, Josh Poimboeuf wrote:
> Thanks to a recent binutils change which doesn't generate unused
> symbols, it's now possible for thunk_64.o be completely empty with
> CONFIG_PREEMPTION: no text, no data, no symbols.
"without CONFIG_PREEMPTION", or did I misunderstand?
> We could edit the Makefile to only build that file when
> CONFIG_PREEMPTION is enabled, but that will likely create confusion
> if/when the thunks end up getting used by some other code again.
>
> Just ignore it and move on.
>
> Reported-by: Nathan Chancellor <natechancel...@gmail.com>
> Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
Reviewed-by: Miroslav Benes <mbe...@suse.cz>
with the note below.
> ---
> tools/objtool/elf.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index be89c741ba9a..2b0f4f52f7b5 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -380,8 +380,11 @@ static int read_symbols(struct elf *elf)
>
> symtab = find_section_by_name(elf, ".symtab");
> if (!symtab) {
> - WARN("missing symbol table");
> - return -1;
> + /*
> + * A missing symbol table is actually possible if it's an empty
> + * .o file. This can happen for thunk_64.o.
> + */
> + return 0;
> }
We rely on .symtab presence elsewhere in the code. See
elf_create_{rel,rela}_reloc_section(). However, there should never be a
problem. If there is a need to create a new reloc section (either for a
static call site, or ORC), there should always be a symbol to create it
for (or because of it).
Miroslav
