objtool/LoongArch: Enable objtool to be built

commit e8aff71ca93026209dd0eab9b285e6808cd87d05 upstream.

Add the minimal changes to enable objtool build on LoongArch,
most of the functions are stubs to only fix the build errors
when make -C tools/objtool.

This is similar with commit e52ec98c5a ("objtool/powerpc:
Enable objtool to be built on ppc").

Co-developed-by: Jinyang He <hejinyang@loongson.cn>
Signed-off-by: Jinyang He <hejinyang@loongson.cn>
Co-developed-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Youling Tang <tangyouling@loongson.cn>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

tools/objtool/arch/loongarch/Build

@@ -0,0 +1,2 @@
+objtool-y += decode.o
+objtool-y += special.o

tools/objtool/arch/loongarch/decode.c

@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <string.h>
+#include <objtool/check.h>
+
+int arch_ftrace_match(char *name)
+{
+	return !strcmp(name, "_mcount");
+}
+
+unsigned long arch_jump_destination(struct instruction *insn)
+{
+	return insn->offset + (insn->immediate << 2);
+}
+
+unsigned long arch_dest_reloc_offset(int addend)
+{
+	return addend;
+}
+
+bool arch_pc_relative_reloc(struct reloc *reloc)
+{
+	return false;
+}
+
+bool arch_callee_saved_reg(unsigned char reg)
+{
+	switch (reg) {
+	case CFI_RA:
+	case CFI_FP:
+	case CFI_S0 ... CFI_S8:
+		return true;
+	default:
+		return false;
+	}
+}
+
+int arch_decode_hint_reg(u8 sp_reg, int *base)
+{
+	return 0;
+}
+
+int arch_decode_instruction(struct objtool_file *file, const struct section *sec,
+			    unsigned long offset, unsigned int maxlen,
+			    struct instruction *insn)
+{
+	return 0;
+}
+
+const char *arch_nop_insn(int len)
+{
+	return NULL;
+}
+
+const char *arch_ret_insn(int len)
+{
+	return NULL;
+}
+
+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;
+}

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

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _OBJTOOL_ARCH_CFI_REGS_H
+#define _OBJTOOL_ARCH_CFI_REGS_H
+
+#define CFI_RA		1
+#define CFI_SP		3
+#define CFI_A0		4
+#define CFI_FP		22
+#define CFI_S0		23
+#define CFI_S1		24
+#define CFI_S2		25
+#define CFI_S3		26
+#define CFI_S4		27
+#define CFI_S5		28
+#define CFI_S6		29
+#define CFI_S7		30
+#define CFI_S8		31
+#define CFI_NUM_REGS	32
+
+#define CFI_BP		CFI_FP
+
+#endif /* _OBJTOOL_ARCH_CFI_REGS_H */

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

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _OBJTOOL_ARCH_ELF_H
+#define _OBJTOOL_ARCH_ELF_H
+
+/*
+ * See the following link for more info about ELF Relocation types:
+ * https://loongson.github.io/LoongArch-Documentation/LoongArch-ELF-ABI-EN.html#_relocations
+ */
+#ifndef R_LARCH_NONE
+#define R_LARCH_NONE		0
+#endif
+#ifndef R_LARCH_32
+#define R_LARCH_32		1
+#endif
+#ifndef R_LARCH_64
+#define R_LARCH_64		2
+#endif
+#ifndef R_LARCH_32_PCREL
+#define R_LARCH_32_PCREL	99
+#endif
+
+#define R_NONE			R_LARCH_NONE
+#define R_ABS32			R_LARCH_32
+#define R_ABS64			R_LARCH_64
+#define R_DATA32		R_LARCH_32_PCREL
+#define R_DATA64		R_LARCH_32_PCREL
+#define R_TEXT32		R_LARCH_32_PCREL
+#define R_TEXT64		R_LARCH_32_PCREL
+
+#endif /* _OBJTOOL_ARCH_ELF_H */

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

@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _OBJTOOL_ARCH_SPECIAL_H
+#define _OBJTOOL_ARCH_SPECIAL_H
+
+/*
+ * See more info about struct exception_table_entry
+ * in arch/loongarch/include/asm/extable.h
+ */
+#define EX_ENTRY_SIZE		12
+#define EX_ORIG_OFFSET		0
+#define EX_NEW_OFFSET		4
+
+/*
+ * See more info about struct jump_entry
+ * in include/linux/jump_label.h
+ */
+#define JUMP_ENTRY_SIZE		16
+#define JUMP_ORIG_OFFSET	0
+#define JUMP_NEW_OFFSET		4
+#define JUMP_KEY_OFFSET		8
+
+/*
+ * See more info about struct alt_instr
+ * in arch/loongarch/include/asm/alternative.h
+ */
+#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 /* _OBJTOOL_ARCH_SPECIAL_H */

tools/objtool/arch/loongarch/special.c

@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+#include <objtool/special.h>
+
+bool arch_support_alt_relocation(struct special_alt *special_alt,
+				 struct instruction *insn,
+				 struct reloc *reloc)
+{
+	return false;
+}
+
+struct reloc *arch_find_switch_table(struct objtool_file *file,
+				     struct instruction *insn)
+{
+	return NULL;
+}