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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 4adb236867 ("objtool: Ignore extra-symbol code") was supposed
to have dealt with that, but the new commit 9f2899fe36 ("objtool:
Add option to generate prefix symbols") subtly broke that logic by
created unvisited symbols.

Fixes: 9f2899fe36 ("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>
This commit is contained in:
Peter Zijlstra 2022-11-03 20:57:51 +01:00
parent 19526717f7
commit 023f2340f0
1 changed files with 21 additions and 1 deletions
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22
tools/objtool/check.c
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@ -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;