objtool: fix build failure due to missing libopcodes check

Commit 5995330 ("objtool: Disassemble code with libopcodes instead
of running objdump") added support for using libopcodes for disassembly.
However, the feature detection checks for libbfd availability but then
unconditionally links against libopcodes:

  ifeq ($(feature-libbfd),1)
      OBJTOOL_LDFLAGS += -lopcodes
  endif

This causes build failures in environments where libbfd is installed but
libopcodes is not, since the test-libbfd.c feature test only links
against -lbfd and -ldl, not -lopcodes:

  /usr/bin/ld: cannot find -lopcodes: No such file or directory
  collect2: error: ld returned 1 exit status
  make[4]: *** [Makefile:109: objtool] Error 1

Additionally, the shared feature framework uses $(CC) which is the
cross-compiler in cross-compilation builds. Since objtool is a host tool
that links with $(HOSTCC) against host libraries, the feature detection
can falsely report libopcodes as available when the cross-compiler's
sysroot has it but the host system doesn't.

Fix this by replacing the feature framework check with a direct inline
test that uses $(HOSTCC) to compile and link a test program against
libopcodes, similar to how xxhash availability is detected.

Fixes: 5995330 ("objtool: Disassemble code with libopcodes instead of running objdump")
Assisted-by: claude-opus-4-5-20251101
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251223120357.2492008-1-sashal@kernel.org

Author: Sasha Levin

tools/objtool/Makefile

@@ -72,23 +72,27 @@ HOST_OVERRIDES := CC="$(HOSTCC)" LD="$(HOSTLD)" AR="$(HOSTAR)"
 
 #
 # To support disassembly, objtool needs libopcodes which is provided
-# with libbdf (binutils-dev or binutils-devel package).
+# with libbfd (binutils-dev or binutils-devel package).
 #
-FEATURE_USER = .objtool
-FEATURE_TESTS = libbfd disassembler-init-styled
-FEATURE_DISPLAY =
-include $(srctree)/tools/build/Makefile.feature
+# We check using HOSTCC directly rather than the shared feature framework
+# because objtool is a host tool that links against host libraries.
+#
+HAVE_LIBOPCODES := $(shell echo 'int main(void) { return 0; }' | \
+			$(HOSTCC) -xc - -o /dev/null -lopcodes 2>/dev/null && echo y)
 
-ifeq ($(feature-disassembler-init-styled), 1)
-	OBJTOOL_CFLAGS += -DDISASM_INIT_STYLED
-endif
+# Styled disassembler support requires binutils >= 2.39
+HAVE_DISASM_STYLED := $(shell echo '$(pound)include <dis-asm.h>' | \
+			$(HOSTCC) -E -xc - 2>/dev/null | grep -q disassembler_style && echo y)
 
 BUILD_DISAS := n
 
-ifeq ($(feature-libbfd),1)
+ifeq ($(HAVE_LIBOPCODES),y)
 	BUILD_DISAS := y
-	OBJTOOL_CFLAGS += -DDISAS -DPACKAGE="objtool"
+	OBJTOOL_CFLAGS += -DDISAS -DPACKAGE='"objtool"'
 	OBJTOOL_LDFLAGS += -lopcodes
+ifeq ($(HAVE_DISASM_STYLED),y)
+	OBJTOOL_CFLAGS += -DDISASM_INIT_STYLED
+endif
 endif
 
 export BUILD_DISAS