On Fri, Feb 23, 2024 at 04:45:22PM -0800, Kees Cook wrote:
> Josh, Peter, can you give a clue about what's happened here? For
> added context, the referenced commit is changing a noreturn function
> prototype[1], which I know gets some special objtool handling, but it's
> converting a pointer arg to a u8... I can't imagine what has gone weird
> here. :P
I think this convinced GCC to reshuffle some basic blocks, which
uncovered an objtool bug. Or, objtool just wasn't smart enough, as the
warning says ;-)
This should fix it, absent any more warnings. Kees, feel free to take
it in your branch if that helps.
---8<---
From: Josh Poimboeuf <[email protected]>
Subject: [PATCH] objtool: Fix UNWIND_HINT_{SAVE,RESTORE} across basic blocks
If SAVE and RESTORE unwind hints are in different basic blocks, and
objtool sees the RESTORE before the SAVE, it errors out with:
vmlinux.o: warning: objtool: vmw_port_hb_in+0x242: objtool isn't smart enough to handle this CFI save/restore combo
In such a case, defer following the RESTORE block until the
straight-line path gets followed later.
Fixes: 8faea26e6111 ("objtool: Re-add UNWIND_HINT_{SAVE_RESTORE}")
Reported-by: kernel test robot <[email protected]>
Closes: https://lore.kernel.org/oe-kbuild-all/[email protected]/
Signed-off-by: Josh Poimboeuf <[email protected]>
---
tools/objtool/check.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 548ec3cd7c00..c4c2f75eadfd 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -3620,6 +3620,18 @@ static int validate_branch(struct objtool_file *file, struct symbol *func,
}
if (!save_insn->visited) {
+ /*
+ * If the restore hint insn is at the
+ * beginning of a basic block and was
+ * branched to from elsewhere, and the
+ * save insn hasn't been visited yet,
+ * defer following this branch for now.
+ * It will be seen later via the
+ * straight-line path.
+ */
+ if (!prev_insn)
+ return 0;
+
WARN_INSN(insn, "objtool isn't smart enough to handle this CFI save/restore combo");
return 1;
}
--
2.43.0
On Mon, Feb 26, 2024 at 11:35:27PM -0800, Josh Poimboeuf wrote:
> On Fri, Feb 23, 2024 at 04:45:22PM -0800, Kees Cook wrote:
> > Josh, Peter, can you give a clue about what's happened here? For
> > added context, the referenced commit is changing a noreturn function
> > prototype[1], which I know gets some special objtool handling, but it's
> > converting a pointer arg to a u8... I can't imagine what has gone weird
> > here. :P
>
> I think this convinced GCC to reshuffle some basic blocks, which
> uncovered an objtool bug. Or, objtool just wasn't smart enough, as the
> warning says ;-)
>
> This should fix it, absent any more warnings. Kees, feel free to take
> it in your branch if that helps.
Thanks very much! I'll carry it in my tree.
-Kees
--
Kees Cook