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RISC-V: Add section of GOT.PLT for kernel module

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Separate the function symbol address from .plt to .got.plt section.

The original plt entry has trampoline code with symbol address,
there is a 32-bit padding bwtween jar instruction and symbol address.

Extract the symbol address to .got.plt to reduce the module size.

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 16:50:42 +08:00 committed by Palmer Dabbelt
parent ab1ef68e54
commit b8bde0ef12
No known key found for this signature in database
GPG Key ID: EF4CA1502CCBAB41
3 changed files with 45 additions and 17 deletions
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38
arch/riscv/include/asm/module.h
View File

@ -21,6 +21,7 @@ struct mod_section {
struct mod_arch_specific {
struct mod_section got;
struct mod_section plt;
struct mod_section got_plt;
};
struct got_entry {
@ -48,13 +49,10 @@ 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
@ -62,9 +60,8 @@ struct plt_entry {
#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)
static inline struct plt_entry emit_plt_entry(u64 val, u64 plt, u64 got_plt)
{
/*
* U-Type encoding:
@ -78,23 +75,36 @@ static inline struct plt_entry emit_plt_entry(u64 val)
* +------------+------------+--------+----------+----------+
*
*/
u64 offset = got_plt - plt;
u32 hi20 = (offset + 0x800) & 0xfffff000;
u32 lo12 = (offset - hi20);
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
OPC_AUIPC | (REG_T0 << 7) | hi20,
OPC_LD | (lo12 << 20) | (REG_T0 << 15) | (REG_T1 << 7),
OPC_JALR | (REG_T1 << 15)
};
}
static inline struct plt_entry *get_plt_entry(u64 val,
const struct mod_section *sec)
static inline int get_got_plt_idx(u64 val, const struct mod_section *sec)
{
struct plt_entry *plt = (struct plt_entry *)sec->shdr->sh_addr;
struct got_entry *got_plt = (struct got_entry *)sec->shdr->sh_addr;
int i;
for (i = 0; i < sec->num_entries; i++) {
if (plt[i].symbol_addr == val)
return &plt[i];
if (got_plt[i].symbol_addr == val)
return i;
}
return -1;
}
static inline struct plt_entry *get_plt_entry(u64 val,
const struct mod_section *sec_plt,
const struct mod_section *sec_got_plt)
{
struct plt_entry *plt = (struct plt_entry *)sec_plt->shdr->sh_addr;
int got_plt_idx = get_got_plt_idx(val, sec_got_plt);
if (got_plt_idx >= 0)
return plt + got_plt_idx;
else
return NULL;
}

21
arch/riscv/kernel/module-sections.c
View File

@ -30,18 +30,23 @@ u64 module_emit_got_entry(struct module *mod, u64 val)
u64 module_emit_plt_entry(struct module *mod, u64 val)
{
struct mod_section *got_plt_sec = &mod->arch.got_plt;
struct got_entry *got_plt;
struct mod_section *plt_sec = &mod->arch.plt;
struct plt_entry *plt = get_plt_entry(val, plt_sec);
struct plt_entry *plt = get_plt_entry(val, plt_sec, got_plt_sec);
int i = plt_sec->num_entries;
if (plt)
return (u64)plt;
/* There is no duplicate entry, create a new one */
got_plt = (struct got_entry *)got_plt_sec->shdr->sh_addr;
got_plt[i] = emit_got_entry(val);
plt = (struct plt_entry *)plt_sec->shdr->sh_addr;
plt[i] = emit_plt_entry(val);
plt[i] = emit_plt_entry(val, (u64)&plt[i], (u64)&got_plt[i]);
plt_sec->num_entries++;
got_plt_sec->num_entries++;
BUG_ON(plt_sec->num_entries > plt_sec->max_entries);
return (u64)&plt[i];
@ -94,6 +99,8 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
mod->arch.plt.shdr = sechdrs + i;
else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
mod->arch.got.shdr = sechdrs + i;
else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got.plt"))
mod->arch.got_plt.shdr = sechdrs + i;
}
if (!mod->arch.plt.shdr) {
@ -104,6 +111,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
pr_err("%s: module GOT section(s) missing\n", mod->name);
return -ENOEXEC;
}
if (!mod->arch.got_plt.shdr) {
pr_err("%s: module GOT.PLT section(s) missing\n", mod->name);
return -ENOEXEC;
}
/* Calculate the maxinum number of entries */
for (i = 0; i < ehdr->e_shnum; i++) {
@ -135,5 +146,11 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
mod->arch.got.num_entries = 0;
mod->arch.got.max_entries = num_gots;
mod->arch.got_plt.shdr->sh_type = SHT_NOBITS;
mod->arch.got_plt.shdr->sh_flags = SHF_ALLOC;
mod->arch.got_plt.shdr->sh_addralign = L1_CACHE_BYTES;
mod->arch.got_plt.shdr->sh_size = (num_plts + 1) * sizeof(struct got_entry);
mod->arch.got_plt.num_entries = 0;
mod->arch.got_plt.max_entries = num_plts;
return 0;
}

1
arch/riscv/kernel/module.lds
View File

@ -4,4 +4,5 @@
SECTIONS {
.plt (NOLOAD) : { BYTE(0) }
.got (NOLOAD) : { BYTE(0) }
.got.plt (NOLOAD) : { BYTE(0) }
}