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>

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 04807c7f64cc58f7b2e4be1ec1d10b4cf1b018a8..90ff52059794dea8cc4a0c934686c89c783306b3 100644 (file)
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -131,6 +131,10 @@ choice
                bool "medium any code model"
 endchoice
 
+config MODULE_SECTIONS
+       bool
+       select HAVE_MOD_ARCH_SPECIFIC
+
 choice
        prompt "Maximum Physical Memory"
        default MAXPHYSMEM_2GB if 32BIT
@@ -141,6 +145,7 @@ choice
                bool "2GiB"
        config MAXPHYSMEM_128GB
                depends on 64BIT && CMODEL_MEDANY
+               select MODULE_SECTIONS if MODULES
                bool "128GiB"
 endchoice
 

diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 6719dd30ec5b847b58faa3521ea3ccd74fd6dddc..c72d408c05c04f650366147f963b052341a68cee 100644 (file)
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -56,6 +56,11 @@ endif
 ifeq ($(CONFIG_CMODEL_MEDANY),y)
        KBUILD_CFLAGS += -mcmodel=medany
 endif
+ifeq ($(CONFIG_MODULE_SECTIONS),y)
+       KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/riscv/kernel/module.lds
+endif
+
+KBUILD_CFLAGS_MODULE += $(call cc-option,-mno-relax)
 
 # GCC versions that support the "-mstrict-align" option default to allowing
 # unaligned accesses.  While unaligned accesses are explicitly allowed in the

diff --git a/arch/riscv/include/asm/module.h b/arch/riscv/include/asm/module.h
new file mode 100644 (file)
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 */

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index 196f62ffc4288d0f9a905e5ee560a7d426de9f5b..d355e3c182784ccae849a52ce0dfadfc6adc78f9 100644 (file)
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile
@@ -34,6 +34,7 @@ CFLAGS_setup.o := -mcmodel=medany
 obj-$(CONFIG_SMP)              += smpboot.o
 obj-$(CONFIG_SMP)              += smp.o
 obj-$(CONFIG_MODULES)          += module.o
+obj-$(CONFIG_MODULE_SECTIONS)  += module-sections.o
 obj-$(CONFIG_FUNCTION_TRACER)  += mcount.o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER)    += ftrace.o
 

diff --git a/arch/riscv/kernel/module-sections.c b/arch/riscv/kernel/module-sections.c
new file mode 100644 (file)
index 0000000..94ba155
--- /dev/null
+++ b/arch/riscv/kernel/module-sections.c
@@ -0,0 +1,139 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * Copyright (C) 2014-2017 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * Copyright (C) 2018 Andes Technology Corporation <zong@andestech.com>
+ */
+
+#include <linux/elf.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+
+u64 module_emit_got_entry(struct module *mod, u64 val)
+{
+       struct mod_section *got_sec = &mod->arch.got;
+       int i = got_sec->num_entries;
+       struct got_entry *got = get_got_entry(val, got_sec);
+
+       if (got)
+               return (u64)got;
+
+       /* There is no duplicate entry, create a new one */
+       got = (struct got_entry *)got_sec->shdr->sh_addr;
+       got[i] = emit_got_entry(val);
+
+       got_sec->num_entries++;
+       BUG_ON(got_sec->num_entries > got_sec->max_entries);
+
+       return (u64)&got[i];
+}
+
+u64 module_emit_plt_entry(struct module *mod, u64 val)
+{
+       struct mod_section *plt_sec = &mod->arch.plt;
+       struct plt_entry *plt = get_plt_entry(val, plt_sec);
+       int i = plt_sec->num_entries;
+
+       if (plt)
+               return (u64)plt;
+
+       /* There is no duplicate entry, create a new one */
+       plt = (struct plt_entry *)plt_sec->shdr->sh_addr;
+       plt[i] = emit_plt_entry(val);
+
+       plt_sec->num_entries++;
+       BUG_ON(plt_sec->num_entries > plt_sec->max_entries);
+
+       return (u64)&plt[i];
+}
+
+static int is_rela_equal(const Elf64_Rela *x, const Elf64_Rela *y)
+{
+       return x->r_info == y->r_info && x->r_addend == y->r_addend;
+}
+
+static bool duplicate_rela(const Elf64_Rela *rela, int idx)
+{
+       int i;
+       for (i = 0; i < idx; i++) {
+               if (is_rela_equal(&rela[i], &rela[idx]))
+                       return true;
+       }
+       return false;
+}
+
+static void count_max_entries(Elf64_Rela *relas, int num,
+                             unsigned int *plts, unsigned int *gots)
+{
+       unsigned int type, i;
+
+       for (i = 0; i < num; i++) {
+               type = ELF64_R_TYPE(relas[i].r_info);
+               if (type == R_RISCV_CALL_PLT) {
+                       if (!duplicate_rela(relas, i))
+                               (*plts)++;
+               } else if (type == R_RISCV_GOT_HI20) {
+                       if (!duplicate_rela(relas, i))
+                               (*gots)++;
+               }
+       }
+}
+
+int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
+                             char *secstrings, struct module *mod)
+{
+       unsigned int num_plts = 0;
+       unsigned int num_gots = 0;
+       int i;
+
+       /*
+        * Find the empty .got and .plt sections.
+        */
+       for (i = 0; i < ehdr->e_shnum; i++) {
+               if (!strcmp(secstrings + sechdrs[i].sh_name, ".plt"))
+                       mod->arch.plt.shdr = sechdrs + i;
+               else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
+                       mod->arch.got.shdr = sechdrs + i;
+       }
+
+       if (!mod->arch.plt.shdr) {
+               pr_err("%s: module PLT section(s) missing\n", mod->name);
+               return -ENOEXEC;
+       }
+       if (!mod->arch.got.shdr) {
+               pr_err("%s: module GOT section(s) missing\n", mod->name);
+               return -ENOEXEC;
+       }
+
+       /* Calculate the maxinum number of entries */
+       for (i = 0; i < ehdr->e_shnum; i++) {
+               Elf64_Rela *relas = (void *)ehdr + sechdrs[i].sh_offset;
+               int num_rela = sechdrs[i].sh_size / sizeof(Elf64_Rela);
+               Elf64_Shdr *dst_sec = sechdrs + sechdrs[i].sh_info;
+
+               if (sechdrs[i].sh_type != SHT_RELA)
+                       continue;
+
+               /* ignore relocations that operate on non-exec sections */
+               if (!(dst_sec->sh_flags & SHF_EXECINSTR))
+                       continue;
+
+               count_max_entries(relas, num_rela, &num_plts, &num_gots);
+       }
+
+       mod->arch.plt.shdr->sh_type = SHT_NOBITS;
+       mod->arch.plt.shdr->sh_flags = SHF_EXECINSTR | SHF_ALLOC;
+       mod->arch.plt.shdr->sh_addralign = L1_CACHE_BYTES;
+       mod->arch.plt.shdr->sh_size = (num_plts + 1) * sizeof(struct plt_entry);
+       mod->arch.plt.num_entries = 0;
+       mod->arch.plt.max_entries = num_plts;
+
+       mod->arch.got.shdr->sh_type = SHT_NOBITS;
+       mod->arch.got.shdr->sh_flags = SHF_ALLOC;
+       mod->arch.got.shdr->sh_addralign = L1_CACHE_BYTES;
+       mod->arch.got.shdr->sh_size = (num_gots + 1) * sizeof(struct got_entry);
+       mod->arch.got.num_entries = 0;
+       mod->arch.got.max_entries = num_gots;
+
+       return 0;
+}

diff --git a/arch/riscv/kernel/module.lds b/arch/riscv/kernel/module.lds
new file mode 100644 (file)
index 0000000..7ef580e
--- /dev/null
+++ b/arch/riscv/kernel/module.lds
@@ -0,0 +1,7 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright (C) 2017 Andes Technology Corporation */
+
+SECTIONS {
+       .plt (NOLOAD) : { BYTE(0) }
+       .got (NOLOAD) : { BYTE(0) }
+}