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

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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>
This commit is contained in:
Zong Li 2018-03-15 16:50:41 +08:00 • committed by Palmer Dabbelt
parent 0adb32858b
commit ab1ef68e54
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139
arch/riscv/kernel/module-sections.c Normal file
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/* 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;
}