The following commit has been merged into the x86/core branch of tip:
Commit-ID: 023f2340f053537cce170c31c430b0886c6f07ca
Gitweb: https://git.kernel.org/tip/023f2340f053537cce170c31c430b0886c6f07ca
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 03 Nov 2022 20:57:51 +01:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Sat, 05 Nov 2022 11:28:02 +01:00
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 4adb23686795 ("objtool: Ignore extra-symbol code") was supposed
to have dealt with that, but the new commit 9f2899fe36a6 ("objtool:
Add option to generate prefix symbols") subtly broke that logic by
created unvisited symbols.
Fixes: 9f2899fe36a6 ("objtool: Add option to generate prefix symbols")
Reported-by: Borislav Petkov <bp@xxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
tools/objtool/check.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 55066c4..4f1a738 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -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;
|