Commit b8bde0ef authored by Zong Li's avatar Zong Li Committed by Palmer Dabbelt

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

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: default avatarZong Li <zong@andestech.com>
Signed-off-by: default avatarPalmer Dabbelt <palmer@sifive.com>
parent ab1ef68e
...@@ -21,6 +21,7 @@ struct mod_section { ...@@ -21,6 +21,7 @@ struct mod_section {
struct mod_arch_specific { struct mod_arch_specific {
struct mod_section got; struct mod_section got;
struct mod_section plt; struct mod_section plt;
struct mod_section got_plt;
}; };
struct got_entry { struct got_entry {
...@@ -48,13 +49,10 @@ struct plt_entry { ...@@ -48,13 +49,10 @@ struct plt_entry {
/* /*
* Trampoline code to real target address. The return address * Trampoline code to real target address. The return address
* should be the original (pc+4) before entring plt entry. * 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_auipc; /* auipc t0, 0x0 */
u32 insn_ld; /* ld t1, 0x10(t0) */ u32 insn_ld; /* ld t1, 0x10(t0) */
u32 insn_jr; /* jr t1 */ u32 insn_jr; /* jr t1 */
u64 symbol_addr; /* the real jump target address */
}; };
#define OPC_AUIPC 0x0017 #define OPC_AUIPC 0x0017
...@@ -62,9 +60,8 @@ struct plt_entry { ...@@ -62,9 +60,8 @@ struct plt_entry {
#define OPC_JALR 0x0067 #define OPC_JALR 0x0067
#define REG_T0 0x5 #define REG_T0 0x5
#define REG_T1 0x6 #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: * U-Type encoding:
...@@ -78,24 +75,37 @@ static inline struct plt_entry emit_plt_entry(u64 val) ...@@ -78,24 +75,37 @@ 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) { return (struct plt_entry) {
OPC_AUIPC | (REG_T0 << 7), OPC_AUIPC | (REG_T0 << 7) | hi20,
OPC_LD | (IMM_OFFSET << 20) | (REG_T0 << 15) | (REG_T1 << 7), OPC_LD | (lo12 << 20) | (REG_T0 << 15) | (REG_T1 << 7),
OPC_JALR | (REG_T1 << 15), OPC_JALR | (REG_T1 << 15)
val
}; };
} }
static inline struct plt_entry *get_plt_entry(u64 val, static inline int get_got_plt_idx(u64 val, const struct mod_section *sec)
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; int i;
for (i = 0; i < sec->num_entries; i++) { for (i = 0; i < sec->num_entries; i++) {
if (plt[i].symbol_addr == val) if (got_plt[i].symbol_addr == val)
return &plt[i]; return i;
} }
return NULL; 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;
} }
#endif /* CONFIG_MODULE_SECTIONS */ #endif /* CONFIG_MODULE_SECTIONS */
......
...@@ -30,18 +30,23 @@ u64 module_emit_got_entry(struct module *mod, u64 val) ...@@ -30,18 +30,23 @@ u64 module_emit_got_entry(struct module *mod, u64 val)
u64 module_emit_plt_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 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; int i = plt_sec->num_entries;
if (plt) if (plt)
return (u64)plt; return (u64)plt;
/* There is no duplicate entry, create a new one */ /* 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 = (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++; plt_sec->num_entries++;
got_plt_sec->num_entries++;
BUG_ON(plt_sec->num_entries > plt_sec->max_entries); BUG_ON(plt_sec->num_entries > plt_sec->max_entries);
return (u64)&plt[i]; return (u64)&plt[i];
...@@ -94,6 +99,8 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, ...@@ -94,6 +99,8 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
mod->arch.plt.shdr = sechdrs + i; mod->arch.plt.shdr = sechdrs + i;
else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got")) else if (!strcmp(secstrings + sechdrs[i].sh_name, ".got"))
mod->arch.got.shdr = sechdrs + i; 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) { if (!mod->arch.plt.shdr) {
...@@ -104,6 +111,10 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, ...@@ -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); pr_err("%s: module GOT section(s) missing\n", mod->name);
return -ENOEXEC; 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 */ /* Calculate the maxinum number of entries */
for (i = 0; i < ehdr->e_shnum; i++) { for (i = 0; i < ehdr->e_shnum; i++) {
...@@ -135,5 +146,11 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs, ...@@ -135,5 +146,11 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
mod->arch.got.num_entries = 0; mod->arch.got.num_entries = 0;
mod->arch.got.max_entries = num_gots; 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; return 0;
} }
...@@ -4,4 +4,5 @@ ...@@ -4,4 +4,5 @@
SECTIONS { SECTIONS {
.plt (NOLOAD) : { BYTE(0) } .plt (NOLOAD) : { BYTE(0) }
.got (NOLOAD) : { BYTE(0) } .got (NOLOAD) : { BYTE(0) }
.got.plt (NOLOAD) : { BYTE(0) }
} }
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