Commit 023f2340 authored Nov 03, 2022 by Peter Zijlstra

objtool: Fix weak hole vs prefix symbol



Boris (and the robot) reported that objtool grew a new complaint about
unreachable instructions. Upon inspection it was immediately clear
the __weak zombie instructions struck again.

For the unweary, the linker will simply remove the symbol for
overriden __weak symbols but leave the instructions in place, creating
unreachable instructions -- and objtool likes to report these.

Commit 4adb2368 ("objtool: Ignore extra-symbol code") was supposed
to have dealt with that, but the new commit 9f2899fe ("objtool:
Add option to generate prefix symbols") subtly broke that logic by
created unvisited symbols.

Fixes: 9f2899fe ("objtool: Add option to generate prefix symbols")
Reported-by: Borislav Petkov <bp@alien8.de>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

parent 19526717

tools/objtool/check.c

+21 −1

Original line number	Diff line number	Diff line
		@@ -4053,8 +4053,28 @@ static int add_prefix_symbol(struct objtool_file file, struct symbol func,

		offset = func->offset - prev->offset;
		if (offset >= opts.prefix) {
		if (offset == opts.prefix)
		if (offset == opts.prefix) {
		/*
		* Since the sec->symbol_list is ordered by
		* offset (see elf_add_symbol()) the added
		* symbol will not be seen by the iteration in
		* validate_section().
		*
		* Hence the lack of list_for_each_entry_safe()
		* there.
		*
		* The direct concequence is that prefix symbols
		* don't get visited (because pointless), except
		* for the logic in ignore_unreachable_insn()
		* that needs the terminating insn to be visited
		* otherwise it will report the hole.
		*
		* Hence mark the first instruction of the
		* prefix symbol as visisted.
		*/
		prev->visited \|= VISITED_BRANCH;
		elf_create_prefix_symbol(file->elf, func, opts.prefix);
		}
		break;
		}
		insn = prev;