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>

1 files changed, 54 insertions, 0 deletions

diff --git a/lib/Kconfig.kmsan b/lib/Kconfig.kmsan
new file mode 100644
index 000000000..cae1ddcc1
--- /dev/null
+++ b/lib/Kconfig.kmsan
@@ -0,0 +1,54 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config HAVE_ARCH_KMSAN
+	bool
+
+config HAVE_KMSAN_COMPILER
+	def_bool $(cc-option,-fsanitize=kernel-memory)
+
+config KMSAN
+	bool "KMSAN: detector of uninitialized values use"
+	depends on HAVE_ARCH_KMSAN && HAVE_KMSAN_COMPILER
+	depends on DEBUG_KERNEL && !KASAN && !KCSAN
+	depends on !PREEMPT_RT
+	select STACKDEPOT
+	select STACKDEPOT_ALWAYS_INIT
+	help
+	  KernelMemorySanitizer (KMSAN) is a dynamic detector of uses of
+	  uninitialized values in the kernel. It is based on compiler
+	  instrumentation provided by Clang and thus requires Clang to build.
+
+	  An important note is that KMSAN is not intended for production use,
+	  because it drastically increases kernel memory footprint and slows
+	  the whole system down.
+
+	  See <file:Documentation/dev-tools/kmsan.rst> for more details.
+
+if KMSAN
+
+config KMSAN_CHECK_PARAM_RETVAL
+	bool "Check for uninitialized values passed to and returned from functions"
+	default y
+	help
+	  If the compiler supports -fsanitize-memory-param-retval, KMSAN will
+	  eagerly check every function parameter passed by value and every
+	  function return value.
+
+	  Disabling KMSAN_CHECK_PARAM_RETVAL will result in tracking shadow for
+	  function parameters and return values across function borders. This
+	  is a more relaxed mode, but it generates more instrumentation code and
+	  may potentially report errors in corner cases when non-instrumented
+	  functions call instrumented ones.
+
+config KMSAN_KUNIT_TEST
+	tristate "KMSAN integration test suite" if !KUNIT_ALL_TESTS
+	default KUNIT_ALL_TESTS
+	depends on TRACEPOINTS && KUNIT
+	help
+	  Test suite for KMSAN, testing various error detection scenarios,
+	  and checking that reports are correctly output to console.
+
+	  Say Y here if you want the test to be built into the kernel and run
+	  during boot; say M if you want the test to build as a module; say N
+	  if you are unsure.
+
+endif