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Subject[PATCH 02/11] RISC-V: Add section of GOT.PLT for kernel module
Date
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>
---
arch/riscv/include/asm/module.h | 40 +++++++++++++++++++++++--------------
arch/riscv/kernel/module-sections.c | 21 +++++++++++++++++--
arch/riscv/kernel/module.lds | 1 +
3 files changed, 45 insertions(+), 17 deletions(-)

diff --git a/arch/riscv/include/asm/module.h b/arch/riscv/include/asm/module.h
index bcc48d113deb..016e6a618e83 100644
--- a/arch/riscv/include/asm/module.h
+++ b/arch/riscv/include/asm/module.h
@@ -18,6 +18,7 @@ struct mod_section {
struct mod_arch_specific {
struct mod_section got;
struct mod_section plt;
+ struct mod_section got_plt;
};
#endif

@@ -49,13 +50,10 @@ 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
@@ -63,9 +61,8 @@ 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:
@@ -79,24 +76,37 @@ 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) {
- 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 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 /* _ASM_RISCV_MODULE_H */
diff --git a/arch/riscv/kernel/module-sections.c b/arch/riscv/kernel/module-sections.c
index 94ba1551eac3..bbbd26e19bfd 100644
--- a/arch/riscv/kernel/module-sections.c
+++ b/arch/riscv/kernel/module-sections.c
@@ -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;
}
diff --git a/arch/riscv/kernel/module.lds b/arch/riscv/kernel/module.lds
index 7ef580e62883..295ecfb341a2 100644
--- a/arch/riscv/kernel/module.lds
+++ b/arch/riscv/kernel/module.lds
@@ -4,4 +4,5 @@
SECTIONS {
.plt (NOLOAD) : { BYTE(0) }
.got (NOLOAD) : { BYTE(0) }
+ .got.plt (NOLOAD) : { BYTE(0) }
}
--
2.16.1
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