objtool: Don't fail on missing symbol table

Thanks to a recent binutils change which doesn't generate unused
symbols, it's now possible for thunk_64.o be completely empty without
CONFIG_PREEMPTION: no text, no data, no symbols.

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>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Tested-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://github.com/ClangBuiltLinux/linux/issues/1254
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index f9682db33ccabbbdd5dd1c0ba493a0d4fd12db31..d8421e1d06bed33f79e8e46d14f7253aa0256102 100644 (file)
--- 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;
        }
 
        symtab_shndx = find_section_by_name(elf, ".symtab_shndx");