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, 72 insertions, 0 deletions

diff --git a/scripts/gcc-plugins/Makefile b/scripts/gcc-plugins/Makefile
new file mode 100644
index 000000000..05b14aba4
--- /dev/null
+++ b/scripts/gcc-plugins/Makefile
@@ -0,0 +1,72 @@
+# SPDX-License-Identifier: GPL-2.0
+
+$(obj)/randomize_layout_plugin.so: $(obj)/randomize_layout_seed.h
+quiet_cmd_create_randomize_layout_seed = SEEDHDR $@
+cmd_create_randomize_layout_seed = \
+	SEED=$$(cat $(filter-out FORCE,$^) </dev/null); \
+	echo '/*' > $@; \
+	echo ' * This file is automatically generated. Keep it private.' >> $@; \
+	echo ' * Exposing this value will expose the layout of randomized structures.' >> $@; \
+	echo ' */' >> $@; \
+	echo "const char *randstruct_seed = \"$$SEED\";" >> $@
+$(obj)/randomize_layout_seed.h: $(objtree)/scripts/basic/randstruct.seed FORCE
+	$(call if_changed,create_randomize_layout_seed)
+targets += randomize_layout_seed.h
+
+# Build rules for plugins
+#
+# No extra code is needed for single-file plugins.
+# For multi-file plugins, use *-objs syntax to list the objects.
+#
+# If the plugin foo.so is compiled from foo.c and foo2.c, you can do:
+#
+# foo-objs := foo.o foo2.o
+
+always-y += $(GCC_PLUGIN)
+
+GCC_PLUGINS_DIR = $(shell $(CC) -print-file-name=plugin)
+
+plugin_cxxflags	= -Wp,-MMD,$(depfile) $(KBUILD_HOSTCXXFLAGS) -fPIC \
+		  -include $(srctree)/include/linux/compiler-version.h \
+		  -DPLUGIN_VERSION=$(call stringify,$(KERNELVERSION)) \
+		  -I $(GCC_PLUGINS_DIR)/include -I $(obj) \
+		  -fno-rtti -fno-exceptions -fasynchronous-unwind-tables \
+		  -ggdb -Wno-narrowing -Wno-unused-variable \
+		  -Wno-format-diag
+
+plugin_ldflags	= -shared
+
+plugin-single	:= $(foreach m, $(GCC_PLUGIN), $(if $($(m:%.so=%-objs)),,$(m)))
+plugin-multi	:= $(filter-out $(plugin-single), $(GCC_PLUGIN))
+plugin-objs	:= $(sort $(foreach m, $(plugin-multi), $($(m:%.so=%-objs))))
+
+targets += $(plugin-single) $(plugin-multi) $(plugin-objs)
+clean-files += *.so
+
+plugin-single	:= $(addprefix $(obj)/, $(plugin-single))
+plugin-multi	:= $(addprefix $(obj)/, $(plugin-multi))
+plugin-objs	:= $(addprefix $(obj)/, $(plugin-objs))
+
+quiet_cmd_plugin_cxx_so_c = HOSTCXX $@
+      cmd_plugin_cxx_so_c = $(HOSTCXX) $(plugin_cxxflags) $(plugin_ldflags) -o $@ $<
+
+$(plugin-single): $(obj)/%.so: $(src)/%.c FORCE
+	$(call if_changed_dep,plugin_cxx_so_c)
+
+quiet_cmd_plugin_ld_so_o = HOSTLD  $@
+      cmd_plugin_ld_so_o = $(HOSTCXX) $(plugin_ldflags) -o $@ \
+			   $(addprefix $(obj)/, $($(target-stem)-objs))
+
+$(plugin-multi): FORCE
+	$(call if_changed,plugin_ld_so_o)
+$(foreach m, $(notdir $(plugin-multi)), $(eval $(obj)/$m: $(addprefix $(obj)/, $($(m:%.so=%-objs)))))
+
+quiet_cmd_plugin_cxx_o_c = HOSTCXX $@
+      cmd_plugin_cxx_o_c = $(HOSTCXX) $(plugin_cxxflags) -c -o $@ $<
+
+$(plugin-objs): $(obj)/%.o: $(src)/%.c FORCE
+	$(call if_changed_dep,plugin_cxx_o_c)
+
+$(obj)/../../include/generated/gcc-plugins.h: $(plugin-single) $(plugin-multi) FORCE
+	$(call if_changed,touch)
+always-y += ../../include/generated/gcc-plugins.h