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SubjectRe: [PATCH] objtool: Don't fail on missing symbol table
On Fri, Jan 15, 2021 at 12:31:26PM +0100, Miroslav Benes wrote:
> 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?

Fixed.

>
> > 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 <natechancellor@gmail.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
>
> Reviewed-by: Miroslav Benes <mbenes@suse.cz>

Thanks!

>
> 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).

Right, let us hope so :-)

--
Josh

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