objtool: Ignore exc_double_fault() __noreturn warnings

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

Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Link: https://lore.kernel.org/r/a45b085071d3a7d049a20f9e78754452336ecbe8.1681853186.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 8d1b4226608c574798df027cbeecab13fabde413..8dac1e35264e0f79ce5fbde004f8cc74a53418fa 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4505,6 +4505,35 @@ 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);
+
+       /*
+        * FIXME: hack, we need a real noreturn solution
+        *
+        * 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:
+        *
+        *   - have compiler communicate __noreturn functions somehow
+        *   - 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
+        */
+       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;
@@ -4521,7 +4550,7 @@ 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++;