objtool: Add --Werror option

JIRA: https://issues.redhat.com/browse/RHEL-85302
Conflicts:
	tools/objtool/builtin-check.c
	tools/objtool/include/objtool/builtin.h
	- Diff context deltas from various missing commits.

commit bb62243
Author: Josh Poimboeuf <jpoimboe@kernel.org>
Date:   Fri Mar 14 12:29:08 2025 -0700

    objtool: Add --Werror option

    Any objtool warning has the potential of reflecting (or triggering) a
    major bug in the kernel or compiler which could result in crashing the
    kernel or breaking the livepatch consistency model.

    In preparation for failing the build on objtool errors/warnings, add a
    new --Werror option.

    [ jpoimboe: commit log, comments, error out on fatal errors too ]

    Co-developed-by: Brendan Jackman <jackmanb@google.com>
    Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Link: https://lore.kernel.org/r/e423ea4ec297f510a108aa6c78b52b9fe30fa8c1.1741975349.git.jpoimboe@kernel.org

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>

Author: joe-lawrence

tools/objtool/builtin-check.c

@@ -99,6 +99,7 @@ const struct option check_options[] = {
 	OPT_STRING('o',  "output", &opts.output, "file", "output file name"),
 	OPT_BOOLEAN(0,   "sec-address", &opts.sec_address, "print section addresses in warnings"),
 	OPT_BOOLEAN(0,   "stats", &opts.stats, "print statistics"),
+	OPT_BOOLEAN(0,   "Werror", &opts.werror, "return error on warnings"),
 
 	OPT_END(),
 };

tools/objtool/check.c

@@ -4641,9 +4641,18 @@ int check(struct objtool_file *file)
 
 out:
 	/*
-	 *  For now, don't fail the kernel build on fatal warnings.  These
-	 *  errors are still fairly common due to the growing matrix of
-	 *  supported toolchains and their recent pace of change.
+	 * CONFIG_OBJTOOL_WERROR upgrades all warnings (and errors) to actual
+	 * errors.
+	 *
+	 * Note that even "fatal" type errors don't actually return an error
+	 * without CONFIG_OBJTOOL_WERROR.  That probably needs improved at some
+	 * point.
 	 */
+	if (opts.werror && (ret || warnings)) {
+		if (warnings)
+			WARN("%d warning(s) upgraded to errors", warnings);
+		return 1;
+	}
+
 	return 0;
 }

tools/objtool/include/objtool/builtin.h

@@ -38,6 +38,7 @@ struct opts {
 	const char *output;
 	bool sec_address;
 	bool stats;
+	bool werror;
 };
 
 extern struct opts opts;