[v2,9/9] objtool: Ignore exc_double_fault() __noreturn warnings
Commit Message
This is a hack, but it works for now.
Problem is, exc_double_fault() may or may not return, depending on
whether CONFIG_X86_ESPFIX64 is set. But objtool has no visibility to
the kernel config.
"Fix" it by silencing the exc_double_fault() __noreturn warning.
This removes the following warning:
vmlinux.o: warning: objtool: xenpv_exc_double_fault+0xd: exc_double_fault() is missing a __noreturn annotation
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
tools/objtool/check.c | 31 ++++++++++++++++++++++++++++++-
1 file changed, 30 insertions(+), 1 deletion(-)
Comments
On Wed, Apr 12, 2023 at 12:03:24PM -0700, Josh Poimboeuf wrote:
> + * - have compiler communicate __noreturn functions somehow
This, we're going to have to do that -- because keeping that (ever
growing) list in sync is going to be a pain in the backside.
On Thu, Apr 13, 2023 at 2:24 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Wed, Apr 12, 2023 at 12:03:24PM -0700, Josh Poimboeuf wrote:
> > + * - have compiler communicate __noreturn functions somehow
Could probably stuff these in some kind of "noreturn function symbol
table"/custom elf section; DWARF tags are nice but we don't always
want debug info. (I should ask colleagues if there's anything like
this in DWARF already, perhaps for DWARFv6).
>
> This, we're going to have to do that -- because keeping that (ever
> growing) list in sync is going to be a pain in the backside.
>
@@ -4483,6 +4483,35 @@ static int validate_sls(struct objtool_file *file)
return warnings;
}
+static bool ignore_noreturn_call(struct instruction *insn)
+{
+ struct symbol *call_dest = insn_call_dest(insn);
+
+ /*
+ * This is a hack, but it works for now.
+ *
+ * Problem is, exc_double_fault() may or may not return, depending on
+ * whether CONFIG_X86_ESPFIX64 is set. But objtool has no visibility
+ * to the kernel config.
+ *
+ * Other potential ways to fix it:
+ *
+ * - remove CONFIG_X86_ESPFIX64
+ * - read the .config file
+ * - add a cmdline option
+ * - create a generic objtool annotation format (vs a bunch of custom
+ * formats) and annotate it
+ * - have compiler communicate __noreturn functions somehow
+ */
+ if (!strcmp(call_dest->name, "exc_double_fault")) {
+ /* prevent further unreachable warnings for the caller */
+ insn->sym->warned = 1;
+ return true;
+ }
+
+ return false;
+}
+
static int validate_reachable_instructions(struct objtool_file *file)
{
struct instruction *insn, *prev_insn;
@@ -4499,7 +4528,7 @@ static int validate_reachable_instructions(struct objtool_file *file)
prev_insn = prev_insn_same_sec(file, insn);
if (prev_insn && prev_insn->dead_end) {
call_dest = insn_call_dest(prev_insn);
- if (call_dest) {
+ if (call_dest && !ignore_noreturn_call(prev_insn)) {
WARN_INSN(insn, "%s() is missing a __noreturn annotation",
call_dest->name);
warnings++;