RISC-V: Add sections of PLT and GOT for kernel module

The address of external symbols will locate more than 32-bit offset
in 64-bit kernel with sv39 or sv48 virtual addressing.

Module loader emits the GOT and PLT entries for data symbols and
function symbols respectively.

The PLT entry is a trampoline code for jumping to the 64-bit
real address. The GOT entry is just the data symbol address.

Signed-off-by: Zong Li <zong@andestech.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

1 files changed, 103 insertions, 0 deletions

diff --git a/arch/riscv/include/asm/module.h b/arch/riscv/include/asm/module.h
new file mode 100644
index 0000000..e61d73f
--- /dev/null
+++ b/arch/riscv/include/asm/module.h
@@ -0,0 +1,103 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2017 Andes Technology Corporation */
+
+#ifndef _ASM_RISCV_MODULE_H
+#define _ASM_RISCV_MODULE_H
+
+#include <asm-generic/module.h>
+
+#define MODULE_ARCH_VERMAGIC    "riscv"
+
+u64 module_emit_got_entry(struct module *mod, u64 val);
+u64 module_emit_plt_entry(struct module *mod, u64 val);
+
+#ifdef CONFIG_MODULE_SECTIONS
+struct mod_section {
+	struct elf64_shdr *shdr;
+	int num_entries;
+	int max_entries;
+};
+
+struct mod_arch_specific {
+	struct mod_section got;
+	struct mod_section plt;
+};
+
+struct got_entry {
+	u64 symbol_addr;	/* the real variable address */
+};
+
+static inline struct got_entry emit_got_entry(u64 val)
+{
+	return (struct got_entry) {val};
+}
+
+static inline struct got_entry *get_got_entry(u64 val,
+					      const struct mod_section *sec)
+{
+	struct got_entry *got = (struct got_entry *)sec->shdr->sh_addr;
+	int i;
+	for (i = 0; i < sec->num_entries; i++) {
+		if (got[i].symbol_addr == val)
+			return &got[i];
+	}
+	return NULL;
+}
+
+struct plt_entry {
+	/*
+	 * Trampoline code to real target address. The return address
+	 * should be the original (pc+4) before entring plt entry.
+	 * For 8 byte alignment of symbol_addr,
+	 * don't pack structure to remove the padding.
+	 */
+	u32 insn_auipc;		/* auipc t0, 0x0                       */
+	u32 insn_ld;		/* ld    t1, 0x10(t0)                  */
+	u32 insn_jr;		/* jr    t1                            */
+	u64 symbol_addr;	/* the real jump target address        */
+};
+
+#define OPC_AUIPC  0x0017
+#define OPC_LD     0x3003
+#define OPC_JALR   0x0067
+#define REG_T0     0x5
+#define REG_T1     0x6
+#define IMM_OFFSET 0x10
+
+static inline struct plt_entry emit_plt_entry(u64 val)
+{
+	/*
+	 * U-Type encoding:
+	 * +------------+----------+----------+
+	 * | imm[31:12] | rd[11:7] | opc[6:0] |
+	 * +------------+----------+----------+
+	 *
+	 * I-Type encoding:
+	 * +------------+------------+--------+----------+----------+
+	 * | imm[31:20] | rs1[19:15] | funct3 | rd[11:7] | opc[6:0] |
+	 * +------------+------------+--------+----------+----------+
+	 *
+	 */
+	return (struct plt_entry) {
+		OPC_AUIPC | (REG_T0 << 7),
+		OPC_LD | (IMM_OFFSET << 20) | (REG_T0 << 15) | (REG_T1 << 7),
+		OPC_JALR | (REG_T1 << 15),
+		val
+	};
+}
+
+static inline struct plt_entry *get_plt_entry(u64 val,
+					      const struct mod_section *sec)
+{
+	struct plt_entry *plt = (struct plt_entry *)sec->shdr->sh_addr;
+	int i;
+	for (i = 0; i < sec->num_entries; i++) {
+		if (plt[i].symbol_addr == val)
+			return &plt[i];
+	}
+	return NULL;
+}
+
+#endif /* CONFIG_MODULE_SECTIONS */
+
+#endif /* _ASM_RISCV_MODULE_H */