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

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

arch/riscv/include/asm/module.h

+25 −15
Original line number Diff line number Diff line
@@ -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;

}

arch/riscv/kernel/module-sections.c

+19 −2
Original line number Diff line number Diff line
@@ -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;

}

arch/riscv/kernel/module.lds

+1 −0
Original line number Diff line number Diff line
@@ -4,4 +4,5 @@ 
SECTIONS {

	.plt (NOLOAD) : { BYTE(0) }

	.got (NOLOAD) : { BYTE(0) }

	.got.plt (NOLOAD) : { BYTE(0) }

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE