objtool: Validate disassembler headers in libopcodes probegrafted

commit 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries")
tested for libopcodes availability by linking a test snippet with a forward
declaration of disassemble_init_for_target().

However, testing symbol linkage with an extern declaration only verifies
the presence of the library (.so/.a) and bypasses checking for development
headers (binutils-dev). On systems where libopcodes is present without
development headers installed, the probe succeeds, enabling BUILD_DISAS.
Subsequent compilation of objtool then fails:

  fatal error: 'bfd.h' file not found
    113 | #include <bfd.h>

Additionally, the probe invokes $(HOSTCC) without $(HOSTCFLAGS), ignoring
any sysroot or include flags specified for the host compiler.

Fix this by including <bfd.h> and <dis-asm.h> directly in the test snippet,
passing $(HOSTCFLAGS) so host compiler options are respected, and defining
PACKAGE="objtool" to satisfy the configuration check in <bfd.h>.

Fixes: 3f2de814c059 ("objtool: Fix libopcodes linking with static libraries")
Fixes: 436326bc525d ("objtool: fix build failure due to missing libopcodes check")
Reported-by: Alice Ryhl <aliceryhl@google.com>
Assisted-by: Antigravity:Gemini-Next
Signed-off-by: Ulises Mendez Martinez <umendez@google.com>
Link: https://patch.msgid.link/20260904150710.2997558-1-umendez@google.com
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>

2 files changed, 60 insertions, 0 deletions

diff --git a/samples/kdb/Makefile b/samples/kdb/Makefile
new file mode 100644
index 000000000..947cb8522
--- /dev/null
+++ b/samples/kdb/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_SAMPLE_KDB) += kdb_hello.o
diff --git a/samples/kdb/kdb_hello.c b/samples/kdb/kdb_hello.c
new file mode 100644
index 000000000..82736e5a5
--- /dev/null
+++ b/samples/kdb/kdb_hello.c
@@ -0,0 +1,58 @@
+/*
+ * Created by: Jason Wessel <jason.wessel@windriver.com>
+ *
+ * Copyright (c) 2010 Wind River Systems, Inc.  All Rights Reserved.
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#include <linux/module.h>
+#include <linux/kdb.h>
+
+/*
+ * All kdb shell command call backs receive argc and argv, where
+ * argv[0] is the command the end user typed
+ */
+static int kdb_hello_cmd(int argc, const char **argv)
+{
+	if (argc > 1)
+		return KDB_ARGCOUNT;
+
+	if (argc)
+		kdb_printf("Hello %s.\n", argv[1]);
+	else
+		kdb_printf("Hello world!\n");
+
+	return 0;
+}
+
+static kdbtab_t hello_cmd = {
+	.name = "hello",
+	.func = kdb_hello_cmd,
+	.usage = "[string]",
+	.help = "Say Hello World or Hello [string]",
+};
+
+static int __init kdb_hello_cmd_init(void)
+{
+	/*
+	 * Registration of a dynamically added kdb command is done with
+	 * kdb_register().
+	 */
+	kdb_register(&hello_cmd);
+	return 0;
+}
+
+static void __exit kdb_hello_cmd_exit(void)
+{
+	kdb_unregister(&hello_cmd);
+}
+
+module_init(kdb_hello_cmd_init);
+module_exit(kdb_hello_cmd_exit);
+
+MODULE_AUTHOR("WindRiver");
+MODULE_DESCRIPTION("KDB example to add a hello command");
+MODULE_LICENSE("GPL");