objtool/powerpc: Enable objtool to be built on ppc

This patch adds [stub] implementations for required functions, inorder
to enable objtool build on powerpc.

[Christophe Leroy: powerpc: Add missing asm/asm.h for objtool,
Use local variables for type and imm in arch_decode_instruction(),
Adapt len for prefixed instructions.]
Tested-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Sathvika Vasireddy <sv@linux.ibm.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20221114175754.1131267-16-sv@linux.ibm.com

arch/powerpc/Kconfig

@@ -238,6 +238,7 @@ config PPC
 	select HAVE_MOD_ARCH_SPECIFIC
 	select HAVE_NMI				if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
 	select HAVE_OPTPROBES
+	select HAVE_OBJTOOL			if PPC32 || MPROFILE_KERNEL
 	select HAVE_PERF_EVENTS
 	select HAVE_PERF_EVENTS_NMI		if PPC64
 	select HAVE_PERF_REGS

arch/powerpc/include/asm/asm.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_POWERPC_ASM_H
+#define _ASM_POWERPC_ASM_H
+
+#define _ASM_PTR	" .long "
+
+#endif /* _ASM_POWERPC_ASM_H */

tools/objtool/arch/powerpc/Build

+objtool-y += decode.o
+objtool-y += special.o

tools/objtool/arch/powerpc/decode.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <objtool/check.h>
+#include <objtool/elf.h>
+#include <objtool/arch.h>
+#include <objtool/warn.h>
+#include <objtool/builtin.h>
+#include <objtool/endianness.h>
+
+unsigned long arch_dest_reloc_offset(int addend)
+{
+	return addend;
+}
+
+bool arch_callee_saved_reg(unsigned char reg)
+{
+	return false;
+}
+
+int arch_decode_hint_reg(u8 sp_reg, int *base)
+{
+	exit(-1);
+}
+
+const char *arch_nop_insn(int len)
+{
+	exit(-1);
+}
+
+const char *arch_ret_insn(int len)
+{
+	exit(-1);
+}
+
+int arch_decode_instruction(struct objtool_file *file, const struct section *sec,
+			    unsigned long offset, unsigned int maxlen,
+			    unsigned int *len, enum insn_type *type,
+			    unsigned long *immediate,
+			    struct list_head *ops_list)
+{
+	unsigned int opcode;
+	enum insn_type typ;
+	unsigned long imm;
+	u32 insn;
+
+	insn = bswap_if_needed(file->elf, *(u32 *)(sec->data->d_buf + offset));
+	opcode = insn >> 26;
+	typ = INSN_OTHER;
+	imm = 0;
+
+	if (opcode == 1)
+		*len = 8;
+	else
+		*len = 4;
+
+	*type = typ;
+	*immediate = imm;
+
+	return 0;
+}
+
+unsigned long arch_jump_destination(struct instruction *insn)
+{
+	return insn->offset + insn->immediate;
+}
+
+void arch_initial_func_cfi_state(struct cfi_init_state *state)
+{
+	int i;
+
+	for (i = 0; i < CFI_NUM_REGS; i++) {
+		state->regs[i].base = CFI_UNDEFINED;
+		state->regs[i].offset = 0;
+	}
+
+	/* initial CFA (call frame address) */
+	state->cfa.base = CFI_SP;
+	state->cfa.offset = 0;
+
+	/* initial LR (return address) */
+	state->regs[CFI_RA].base = CFI_CFA;
+	state->regs[CFI_RA].offset = 0;
+}

tools/objtool/arch/powerpc/include/arch/cfi_regs.h

+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _OBJTOOL_CFI_REGS_H
+#define _OBJTOOL_CFI_REGS_H
+
+#define CFI_BP 1
+#define CFI_SP CFI_BP
+#define CFI_RA 32
+#define CFI_NUM_REGS 33
+
+#endif

tools/objtool/arch/powerpc/include/arch/elf.h

+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#ifndef _OBJTOOL_ARCH_ELF
+#define _OBJTOOL_ARCH_ELF
+
+#define R_NONE R_PPC_NONE
+
+#endif /* _OBJTOOL_ARCH_ELF */

tools/objtool/arch/powerpc/include/arch/special.h

+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _PPC_ARCH_SPECIAL_H
+#define _PPC_ARCH_SPECIAL_H
+
+#define EX_ENTRY_SIZE 8
+#define EX_ORIG_OFFSET 0
+#define EX_NEW_OFFSET 4
+
+#define JUMP_ENTRY_SIZE 16
+#define JUMP_ORIG_OFFSET 0
+#define JUMP_NEW_OFFSET 4
+#define JUMP_KEY_OFFSET 8
+
+#define ALT_ENTRY_SIZE 12
+#define ALT_ORIG_OFFSET 0
+#define ALT_NEW_OFFSET 4
+#define ALT_FEATURE_OFFSET 8
+#define ALT_ORIG_LEN_OFFSET 10
+#define ALT_NEW_LEN_OFFSET 11
+
+#endif /* _PPC_ARCH_SPECIAL_H */

tools/objtool/arch/powerpc/special.c

+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <string.h>
+#include <stdlib.h>
+#include <objtool/special.h>
+#include <objtool/builtin.h>
+
+
+bool arch_support_alt_relocation(struct special_alt *special_alt,
+				 struct instruction *insn,
+				 struct reloc *reloc)
+{
+	exit(-1);
+}
+
+struct reloc *arch_find_switch_table(struct objtool_file *file,
+				    struct instruction *insn)
+{
+	exit(-1);
+}