ubuntu-linux-kernel/arch/mips/vdso/genvdso.h

/*
 * Copyright (C) 2015 Imagination Technologies
 * Author: Alex Smith <alex.smith@imgtec.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation;  either version 2 of the  License, or (at your
 * option) any later version.
 */

static inline bool FUNC(patch_vdso)(const char *path, void *vdso)
{
	const ELF(Ehdr) *ehdr = vdso;
	void *shdrs;
	ELF(Shdr) *shdr;
	char *shstrtab, *name;
	uint16_t sh_count, sh_entsize, i;
	unsigned int local_gotno, symtabno, gotsym;
	ELF(Dyn) *dyn = NULL;

	shdrs = vdso + FUNC(swap_uint)(ehdr->e_shoff);
	sh_count = swap_uint16(ehdr->e_shnum);
	sh_entsize = swap_uint16(ehdr->e_shentsize);

	shdr = shdrs + (sh_entsize * swap_uint16(ehdr->e_shstrndx));
	shstrtab = vdso + FUNC(swap_uint)(shdr->sh_offset);

	for (i = 0; i < sh_count; i++) {
		shdr = shdrs + (i * sh_entsize);
		name = shstrtab + swap_uint32(shdr->sh_name);

		/*
		 * Ensure there are no relocation sections - ld.so does not
		 * relocate the VDSO so if there are relocations things will
		 * break.
		 */
		switch (swap_uint32(shdr->sh_type)) {
		case SHT_REL:
		case SHT_RELA:
			fprintf(stderr,
				"%s: '%s' contains relocation sections\n",
				program_name, path);
			return false;
		case SHT_DYNAMIC:
			dyn = vdso + FUNC(swap_uint)(shdr->sh_offset);
			break;
		}

		/* Check for existing sections. */
		if (strcmp(name, ".MIPS.abiflags") == 0) {
			fprintf(stderr,
				"%s: '%s' already contains a '.MIPS.abiflags' section\n",
				program_name, path);
			return false;
		}

		if (strcmp(name, ".mips_abiflags") == 0) {
			strcpy(name, ".MIPS.abiflags");
			shdr->sh_type = swap_uint32(SHT_MIPS_ABIFLAGS);
			shdr->sh_entsize = shdr->sh_size;
		}
	}

	/*
	 * Ensure the GOT has no entries other than the standard 2, for the same
	 * reason we check that there's no relocation sections above.
	 * The standard two entries are:
	 * - Lazy resolver
	 * - Module pointer
	 */
	if (dyn) {
		local_gotno = symtabno = gotsym = 0;

		while (FUNC(swap_uint)(dyn->d_tag) != DT_NULL) {
			switch (FUNC(swap_uint)(dyn->d_tag)) {
			/*
			 * This member holds the number of local GOT entries.
			 */
			case DT_MIPS_LOCAL_GOTNO:
				local_gotno = FUNC(swap_uint)(dyn->d_un.d_val);
				break;
			/*
			 * This member holds the number of entries in the
			 * .dynsym section.
			 */
			case DT_MIPS_SYMTABNO:
				symtabno = FUNC(swap_uint)(dyn->d_un.d_val);
				break;
			/*
			 * This member holds the index of the first dynamic
			 * symbol table entry that corresponds to an entry in
			 * the GOT.
			 */
			case DT_MIPS_GOTSYM:
				gotsym = FUNC(swap_uint)(dyn->d_un.d_val);
				break;
			}

			dyn++;
		}

		if (local_gotno > 2 || symtabno - gotsym) {
			fprintf(stderr,
				"%s: '%s' contains unexpected GOT entries\n",
				program_name, path);
			return false;
		}
	}

	return true;
}

static inline bool FUNC(get_symbols)(const char *path, void *vdso)
{
	const ELF(Ehdr) *ehdr = vdso;
	void *shdrs, *symtab;
	ELF(Shdr) *shdr;
	const ELF(Sym) *sym;
	char *strtab, *name;
	uint16_t sh_count, sh_entsize, st_count, st_entsize, i, j;
	uint64_t offset;
	uint32_t flags;

	shdrs = vdso + FUNC(swap_uint)(ehdr->e_shoff);
	sh_count = swap_uint16(ehdr->e_shnum);
	sh_entsize = swap_uint16(ehdr->e_shentsize);

	for (i = 0; i < sh_count; i++) {
		shdr = shdrs + (i * sh_entsize);

		if (swap_uint32(shdr->sh_type) == SHT_SYMTAB)
			break;
	}

	if (i == sh_count) {
		fprintf(stderr, "%s: '%s' has no symbol table\n", program_name,
			path);
		return false;
	}

	/* Get flags */
	flags = swap_uint32(ehdr->e_flags);
	if (elf_class == ELFCLASS64)
		elf_abi = ABI_N64;
	else if (flags & EF_MIPS_ABI2)
		elf_abi = ABI_N32;
	else
		elf_abi = ABI_O32;

	/* Get symbol table. */
	symtab = vdso + FUNC(swap_uint)(shdr->sh_offset);
	st_entsize = FUNC(swap_uint)(shdr->sh_entsize);
	st_count = FUNC(swap_uint)(shdr->sh_size) / st_entsize;

	/* Get string table. */
	shdr = shdrs + (swap_uint32(shdr->sh_link) * sh_entsize);
	strtab = vdso + FUNC(swap_uint)(shdr->sh_offset);

	/* Write offsets for symbols needed by the kernel. */
	for (i = 0; vdso_symbols[i].name; i++) {
		if (!(vdso_symbols[i].abis & elf_abi))
			continue;

		for (j = 0; j < st_count; j++) {
			sym = symtab + (j * st_entsize);
			name = strtab + swap_uint32(sym->st_name);

			if (!strcmp(name, vdso_symbols[i].name)) {
				offset = FUNC(swap_uint)(sym->st_value);

				fprintf(out_file,
					"\t.%s = 0x%" PRIx64 ",\n",
					vdso_symbols[i].offset_name, offset);
				break;
			}
		}

		if (j == st_count) {
			fprintf(stderr,
				"%s: '%s' is missing required symbol '%s'\n",
				program_name, path, vdso_symbols[i].name);
			return false;
		}
	}

	return true;
}