objtool: Enable compilation of objtool for all architectures

Objtool currently only compiles for x86 architectures. This is
fine as it presently does not support tooling for other
architectures. However, we would like to be able to convert other
kernel tools to run as objtool sub commands because they too
process ELF object files. This will allow us to convert tools
such as recordmcount to use objtool's ELF code.

Since much of recordmcount's ELF code is copy-paste code to/from
a variety of other kernel tools (look at modpost for example) this
means that if we can convert recordmcount we can convert more.

We define weak definitions for subcommand entry functions and other weak
definitions for shared functions critical to building existing
subcommands. These return 127 when the command is missing which signify
tools that do not exist on all architectures.  In this case the "check"
and "orc" tools do not exist on all architectures so we only add them
for x86. Future changes adding support for "check", to arm64 for
example, can then modify the SUBCMD_CHECK variable when building for
arm64.

Objtool is not currently wired in to KConfig to be built for other
architectures because it's not needed for those architectures and
there are no commands it supports other than those for x86. As more
command support is enabled on various architectures the necessary
KConfig changes can be made (e.g. adding "STACK_VALIDATION") to
trigger building objtool.

[ jpoimboe: remove aliases, add __weak macro, add error messages ]

Cc: Julien Thierry <jthierry@redhat.com>
Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>

tools/objtool/Build

@@ -1,11 +1,16 @@
 objtool-y += arch/$(SRCARCH)/
+
+objtool-y += weak.o
+
+objtool-$(SUBCMD_CHECK) += check.o
+objtool-$(SUBCMD_CHECK) += special.o
+objtool-$(SUBCMD_ORC) += check.o
+objtool-$(SUBCMD_ORC) += orc_gen.o
+objtool-$(SUBCMD_ORC) += orc_dump.o
+
 objtool-y += builtin-check.o
 objtool-y += builtin-orc.o
-objtool-y += check.o
-objtool-y += orc_gen.o
-objtool-y += orc_dump.o
 objtool-y += elf.o
-objtool-y += special.o
 objtool-y += objtool.o
 
 objtool-y += libstring.o

tools/objtool/Makefile

@@ -46,6 +46,16 @@ elfshdr := $(shell echo '$(pound)include <libelf.h>' | $(CC) $(CFLAGS) -x c -E -
 CFLAGS += $(if $(elfshdr),,-DLIBELF_USE_DEPRECATED)
 
 AWK = awk
+
+SUBCMD_CHECK := n
+SUBCMD_ORC := n
+
+ifeq ($(SRCARCH),x86)
+	SUBCMD_CHECK := y
+	SUBCMD_ORC := y
+endif
+
+export SUBCMD_CHECK SUBCMD_ORC
 export srctree OUTPUT CFLAGS SRCARCH AWK
 include $(srctree)/tools/build/Makefile.include
 

tools/objtool/arch.h

@@ -8,9 +8,11 @@
 
 #include <stdbool.h>
 #include <linux/list.h>
-#include "elf.h"
+#include "objtool.h"
 #include "cfi.h"
 
+#include <asm/orc_types.h>
+
 enum insn_type {
 	INSN_JUMP_CONDITIONAL,
 	INSN_JUMP_UNCONDITIONAL,

tools/objtool/builtin-check.c

@@ -16,7 +16,7 @@
 #include <subcmd/parse-options.h>
 #include <string.h>
 #include "builtin.h"
-#include "check.h"
+#include "objtool.h"
 
 bool no_fp, no_unreachable, retpoline, module, backtrace, uaccess, stats, validate_dup, vmlinux;
 

tools/objtool/builtin-orc.c

@@ -14,8 +14,7 @@
 
 #include <string.h>
 #include "builtin.h"
-#include "check.h"
-
+#include "objtool.h"
 
 static const char *orc_usage[] = {
 	"objtool orc generate [<options>] file.o",

tools/objtool/check.c

@@ -7,10 +7,10 @@
 #include <stdlib.h>
 
 #include "builtin.h"
+#include "cfi.h"
+#include "arch.h"
 #include "check.h"
-#include "elf.h"
 #include "special.h"
-#include "arch.h"
 #include "warn.h"
 
 #include <linux/hashtable.h>

tools/objtool/check.h

@@ -7,10 +7,8 @@
 #define _CHECK_H
 
 #include <stdbool.h>
-#include "objtool.h"
 #include "cfi.h"
 #include "arch.h"
-#include "orc.h"
 
 struct insn_state {
 	struct cfi_state cfi;
@@ -47,8 +45,6 @@ struct instruction {
 	struct orc_entry orc;
 };
 
-int check(const char *objname, bool orc);
-
 struct instruction *find_insn(struct objtool_file *file,
 			      struct section *sec, unsigned long offset);
 

tools/objtool/objtool.h

@@ -19,4 +19,9 @@ struct objtool_file {
 	bool ignore_unreachables, c_file, hints, rodata;
 };
 
+int check(const char *objname, bool orc);
+int orc_dump(const char *objname);
+int create_orc(struct objtool_file *file);
+int create_orc_sections(struct objtool_file *file);
+
 #endif /* _OBJTOOL_H */

tools/objtool/orc_dump.c

@@ -4,7 +4,8 @@
  */
 
 #include <unistd.h>
-#include "orc.h"
+#include <asm/orc_types.h>
+#include "objtool.h"
 #include "warn.h"
 
 static const char *reg_name(unsigned int reg)

tools/objtool/orc_gen.c

@@ -6,7 +6,6 @@
 #include <stdlib.h>
 #include <string.h>
 
-#include "orc.h"
 #include "check.h"
 #include "warn.h"
 

tools/objtool/weak.c

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2020 Matt Helsley <mhelsley@vmware.com>
+ * Weak definitions necessary to compile objtool without
+ * some subcommands (e.g. check, orc).
+ */
+
+#include <stdbool.h>
+#include <errno.h>
+#include "objtool.h"
+
+#define __weak __attribute__((weak))
+
+#define UNSUPPORTED(name)						\
+({									\
+	fprintf(stderr, "error: objtool: " name " not implemented\n");	\
+	return ENOSYS;							\
+})
+
+const char __weak *objname;
+
+int __weak check(const char *_objname, bool orc)
+{
+	UNSUPPORTED("check subcommand");
+}
+
+int __weak orc_dump(const char *_objname)
+{
+	UNSUPPORTED("orc");
+}
+
+int __weak create_orc(struct objtool_file *file)
+{
+	UNSUPPORTED("orc");
+}
+
+int __weak create_orc_sections(struct objtool_file *file)
+{
+	UNSUPPORTED("orc");
+}