kpatch/kpatch-build/kpatch-elf.c

/*
 * kpatch-elf.c
 *
 * 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.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA,
 * 02110-1301, USA.
 */

/*
 * This file provides a common api to create, inspect, and manipulate
 * kpatch_elf objects.
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <error.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "asm/insn.h"
#include "kpatch-elf.h"

/*******************
 * Helper functions
 ******************/

char *status_str(enum status status)
{
	switch(status) {
	case NEW:
		return "NEW";
	case CHANGED:
		return "CHANGED";
	case SAME:
		return "SAME";
	default:
		ERROR("status_str");
	}
	/* never reached */
	return NULL;
}

bool is_rela_section(struct section *sec)
{
	return (sec->sh.sh_type == SHT_RELA);
}

bool is_text_section(struct section *sec)
{
	return (sec->sh.sh_type == SHT_PROGBITS &&
		(sec->sh.sh_flags & SHF_EXECINSTR));
}

bool is_debug_section(struct section *sec)
{
	char *name;
	if (is_rela_section(sec))
		name = sec->base->name;
	else
		name = sec->name;

	return !strncmp(name, ".debug_", 7) ||
	       !strncmp(name, ".eh_frame", 9);
}

struct section *find_section_by_index(struct list_head *list, unsigned int index)
{
	struct section *sec;

	list_for_each_entry(sec, list, list)
		if (sec->index == index)
			return sec;

	return NULL;
}

struct section *find_section_by_name(struct list_head *list, const char *name)
{
	struct section *sec;

	list_for_each_entry(sec, list, list)
		if (!strcmp(sec->name, name))
			return sec;

	return NULL;
}

struct symbol *find_symbol_by_index(struct list_head *list, size_t index)
{
	struct symbol *sym;

	list_for_each_entry(sym, list, list)
		if (sym->index == index)
			return sym;

	return NULL;
}

struct symbol *find_symbol_by_name(struct list_head *list, const char *name)
{
	struct symbol *sym;

	list_for_each_entry(sym, list, list)
		if (sym->name && !strcmp(sym->name, name))
			return sym;

	return NULL;
}

struct rela *find_rela_by_offset(struct section *relasec, unsigned int offset)
{
	struct rela *rela;

	list_for_each_entry(rela, &relasec->relas, list) {
		if (rela->offset == offset)
			return rela;
	}

	return NULL;
}

unsigned int absolute_rela_type(struct kpatch_elf *kelf)
{
	switch(kelf->arch) {
	case PPC64:
		return R_PPC64_ADDR64;
	case X86_64:
		return R_X86_64_64;
	case S390:
		return R_390_64;
	default:
		ERROR("unsupported arch");
	}
	return 0;
}

/* returns the offset of the string in the string table */
int offset_of_string(struct list_head *list, char *name)
{
	struct string *string;
	int index = 0;

	/* try to find string in the string list */
	list_for_each_entry(string, list, list) {
		if (!strcmp(string->name, name))
			return index;
		index += (int)strlen(string->name) + 1;
	}

	/* allocate a new string */
	ALLOC_LINK(string, list);
	string->name = name;
	return index;
}

static void rela_insn(const struct section *sec, const struct rela *rela,
		      struct insn *insn)
{
	unsigned long insn_addr, start, end, rela_addr;

	start = (unsigned long)sec->data->d_buf;
	end = start + sec->sh.sh_size;

	if (end <= start)
		ERROR("bad section size");

	rela_addr = start + rela->offset;
	for (insn_addr = start; insn_addr < end; insn_addr += insn->length) {
		insn_init(insn, (void *)insn_addr, 1);
		insn_get_length(insn);
		if (!insn->length)
			ERROR("can't decode instruction in section %s at offset 0x%lx",
			      sec->name, insn_addr);
		if (rela_addr >= insn_addr &&
		    rela_addr < insn_addr + insn->length)
			return;
	}

	ERROR("can't find instruction for rela at %s+0x%x",
	      sec->name, rela->offset);
}

/*
 * Return the addend, adjusted for any PC-relative relocation trickery, to
 * point to the relevant symbol offset.
 */
long rela_target_offset(struct kpatch_elf *kelf, struct section *relasec,
			struct rela *rela)
{
	long add_off;
	struct section *sec = relasec->base;

	switch(kelf->arch) {
	case PPC64:
		add_off = 0;
		break;
	case X86_64:
		if (!is_text_section(sec) ||
		    rela->type == R_X86_64_64 ||
		    rela->type == R_X86_64_32S)
			add_off = 0;
		else if (rela->type == R_X86_64_PC32 ||
			 rela->type == R_X86_64_PLT32 ||
			 rela->type == R_X86_64_NONE) {
			struct insn insn;
			rela_insn(sec, rela, &insn);
			add_off = (long)insn.next_byte -
				  (long)sec->data->d_buf -
				  rela->offset;
		} else
			ERROR("unhandled rela type %d", rela->type);
		break;
	case S390:
		/*
		 * For branch and relative load instructions,
		 * add_off is -2.
		 */
		if (rela->type == R_390_GOTENT ||
			rela->type == R_390_PLT32DBL ||
			rela->type == R_390_PC32DBL)
			add_off = -2;
		else if (rela->type == R_390_32 ||
			rela->type == R_390_64 ||
			rela->type == R_390_PC32 ||
			rela->type == R_390_PC64)
			add_off = 0;
		else
			ERROR("unhandled rela type %d", rela->type);
		break;
	default:
		ERROR("unsupported arch\n");
	}

	return rela->addend + add_off;
}

unsigned int insn_length(struct kpatch_elf *kelf, void *addr)
{
	struct insn decoded_insn;
	char *insn = addr;

	switch(kelf->arch) {

	case X86_64:
		insn_init(&decoded_insn, addr, 1);
		insn_get_length(&decoded_insn);
		return decoded_insn.length;

	case PPC64:
		return 4;

	case S390:
		switch(insn[0] >> 6) {
		case 0:
			return 2;
		case 1:
		case 2:
			return 4;
		case 3:
			return 6;
		}

	default:
		ERROR("unsupported arch");
	}

	return 0;
}

static void kpatch_create_rela_list(struct kpatch_elf *kelf,
				    struct section *relasec)
{
	int index = 0, skip = 0;
	struct rela *rela;
	unsigned int symndx;
	unsigned long rela_nr;

	/* find matching base (text/data) section */
	relasec->base = find_section_by_index(&kelf->sections, relasec->sh.sh_info);
	if (!relasec->base)
		ERROR("can't find base section for rela section %s", relasec->name);

	/* create reverse link from base section to this rela section */
	relasec->base->rela = relasec;

	rela_nr = relasec->sh.sh_size / relasec->sh.sh_entsize;

	log_debug("\n=== rela list for %s (%ld entries) ===\n",
		relasec->base->name, rela_nr);

	if (is_debug_section(relasec)) {
		log_debug("skipping rela listing for .debug_* section\n");
		skip = 1;
	}

	/* read and store the rela entries */
	while (rela_nr--) {
		ALLOC_LINK(rela, &relasec->relas);

		if (!gelf_getrela(relasec->data, index, &rela->rela))
			ERROR("gelf_getrela");
		index++;

		rela->type = GELF_R_TYPE(rela->rela.r_info);
		rela->addend = rela->rela.r_addend;
		rela->offset = (unsigned int)rela->rela.r_offset;
		symndx = (unsigned int)GELF_R_SYM(rela->rela.r_info);
		rela->sym = find_symbol_by_index(&kelf->symbols, symndx);
		if (!rela->sym)
			ERROR("could not find rela entry symbol\n");
		if (rela->sym->sec &&
		    (rela->sym->sec->sh.sh_flags & SHF_STRINGS)) {
			rela->string = rela->sym->sec->data->d_buf +
				       rela->sym->sym.st_value +
				       rela_target_offset(kelf, relasec, rela);
			if (!rela->string)
				ERROR("could not lookup rela string for %s+%ld",
				      rela->sym->name, rela->addend);
		}

		if (skip)
			continue;
		log_debug("offset %d, type %d, %s %s %ld", rela->offset,
			rela->type, rela->sym->name,
			(rela->addend < 0)?"-":"+", labs(rela->addend));
		if (rela->string)
			log_debug(" (string = %s)", rela->string);
		log_debug("\n");
	}
}

static void kpatch_create_section_list(struct kpatch_elf *kelf)
{
	Elf_Scn *scn = NULL;
	struct section *sec;
	size_t shstrndx, sections_nr;

	if (elf_getshdrnum(kelf->elf, &sections_nr))
		ERROR("elf_getshdrnum");

	/*
	 * elf_getshdrnum() includes section index 0 but elf_nextscn
	 * doesn't return that section so subtract one.
	 */
	sections_nr--;

	if (elf_getshdrstrndx(kelf->elf, &shstrndx))
		ERROR("elf_getshdrstrndx");

	log_debug("=== section list (%zu) ===\n", sections_nr);

	while (sections_nr--) {
		ALLOC_LINK(sec, &kelf->sections);

		scn = elf_nextscn(kelf->elf, scn);
		if (!scn)
			ERROR("scn NULL");

		if (!gelf_getshdr(scn, &sec->sh))
			ERROR("gelf_getshdr");

		sec->name = elf_strptr(kelf->elf, shstrndx, sec->sh.sh_name);
		if (!sec->name)
			ERROR("elf_strptr");

		sec->data = elf_getdata(scn, NULL);
		if (!sec->data)
			ERROR("elf_getdata");

		sec->index = (unsigned int)elf_ndxscn(scn);


		if (sec->sh.sh_type == SHT_SYMTAB_SHNDX)
			kelf->symtab_shndx = sec->data;

		log_debug("ndx %02d, data %p, size %zu, name %s\n",
			sec->index, sec->data->d_buf, sec->data->d_size,
			sec->name);
	}

	/* Sanity check, one more call to elf_nextscn() should return NULL */
	if (elf_nextscn(kelf->elf, scn))
		ERROR("expected NULL");
}

static void kpatch_create_symbol_list(struct kpatch_elf *kelf)
{
	struct section *symtab;
	struct symbol *sym;
	unsigned int symbols_nr, index = 0;
	Elf32_Word shndx;

	symtab = find_section_by_name(&kelf->sections, ".symtab");
	if (!symtab)
		ERROR("missing symbol table");

	symbols_nr = (unsigned int)(symtab->sh.sh_size / symtab->sh.sh_entsize);

	log_debug("\n=== symbol list (%d entries) ===\n", symbols_nr);

	while (symbols_nr--) {
		ALLOC_LINK(sym, &kelf->symbols);

		INIT_LIST_HEAD(&sym->children);

		sym->index = index;
		if (!gelf_getsym(symtab->data, index, &sym->sym))
			ERROR("gelf_getsym");
		index++;

		sym->name = elf_strptr(kelf->elf, symtab->sh.sh_link,
				       sym->sym.st_name);
		if (!sym->name)
			ERROR("elf_strptr");

		sym->type = GELF_ST_TYPE(sym->sym.st_info);
		sym->bind = GELF_ST_BIND(sym->sym.st_info);

		shndx = sym->sym.st_shndx;
		if (shndx == SHN_XINDEX &&
		    !gelf_getsymshndx(symtab->data, kelf->symtab_shndx, sym->index, &sym->sym, &shndx))
			ERROR("couldn't find extended section index for symbol %s; idx=%d",
			      sym->name, sym->index);

		if ((sym->sym.st_shndx > SHN_UNDEF &&
		    sym->sym.st_shndx < SHN_LORESERVE) ||
		    sym->sym.st_shndx == SHN_XINDEX) {
			sym->sec = find_section_by_index(&kelf->sections, shndx);
			if (!sym->sec)
				ERROR("couldn't find section for symbol %s\n",
					sym->name);

			if (sym->type == STT_SECTION) {
				sym->sec->secsym = sym;
				/* use the section name as the symbol name */
				sym->name = sym->sec->name;
			}
		}

		log_debug("sym %02d, type %d, bind %d, ndx %02d, name %s",
			sym->index, sym->type, sym->bind, sym->sym.st_shndx,
			sym->name);
		if (sym->sec)
			log_debug(" -> %s", sym->sec->name);
		log_debug("\n");
	}

}

struct kpatch_elf *kpatch_elf_open(const char *name)
{
	Elf *elf;
	int fd;
	struct kpatch_elf *kelf;
	struct section *relasec;
	GElf_Ehdr ehdr;

	fd = open(name, O_RDONLY);
	if (fd == -1)
		ERROR("open");

	elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
	if (!elf)
		ERROR("elf_begin");

	kelf = malloc(sizeof(*kelf));
	if (!kelf)
		ERROR("malloc");
	memset(kelf, 0, sizeof(*kelf));
	INIT_LIST_HEAD(&kelf->sections);
	INIT_LIST_HEAD(&kelf->symbols);
	INIT_LIST_HEAD(&kelf->strings);

	/* read and store section, symbol entries from file */
	kelf->elf = elf;
	kelf->fd = fd;

	if (!gelf_getehdr(kelf->elf, &ehdr))
		ERROR("gelf_getehdr");
	switch (ehdr.e_machine) {
	case EM_PPC64:
		kelf->arch = PPC64;
		break;
	case EM_X86_64:
		kelf->arch = X86_64;
		break;
	case EM_S390:
		kelf->arch = S390;
		break;
	default:
		ERROR("Unsupported target architecture");
	}

	kpatch_create_section_list(kelf);
	kpatch_create_symbol_list(kelf);

	/* for each rela section, read and store the rela entries */
	list_for_each_entry(relasec, &kelf->sections, list) {
		if (!is_rela_section(relasec))
			continue;
		INIT_LIST_HEAD(&relasec->relas);
		kpatch_create_rela_list(kelf, relasec);
	}

	return kelf;
}

void kpatch_dump_kelf(struct kpatch_elf *kelf)
{
	struct section *sec;
	struct symbol *sym;
	struct rela *rela;

	if (loglevel > DEBUG)
		return;

	printf("\n=== Sections ===\n");
	list_for_each_entry(sec, &kelf->sections, list) {
		printf("%02d %s (%s)", sec->index, sec->name, status_str(sec->status));
		if (is_rela_section(sec)) {
			printf(", base-> %s\n", sec->base->name);
			/* skip .debug_* sections */
			if (is_debug_section(sec))
				goto next;
			printf("rela section expansion\n");
			list_for_each_entry(rela, &sec->relas, list) {
				printf("sym %d, offset %d, type %d, %s %s %ld\n",
				       rela->sym->index, rela->offset,
				       rela->type, rela->sym->name,
				       (rela->addend < 0)?"-":"+",
				       labs(rela->addend));
			}
		} else {
			if (sec->sym)
				printf(", sym-> %s", sec->sym->name);
			if (sec->secsym)
				printf(", secsym-> %s", sec->secsym->name);
			if (sec->rela)
				printf(", rela-> %s", sec->rela->name);
		}
next:
		printf("\n");
	}

	printf("\n=== Symbols ===\n");
	list_for_each_entry(sym, &kelf->symbols, list) {
		printf("sym %02d, type %d, bind %d, ndx %02d, name %s (%s)",
			sym->index, sym->type, sym->bind, sym->sym.st_shndx,
			sym->name, status_str(sym->status));
		if (sym->sec && (sym->type == STT_FUNC || sym->type == STT_OBJECT))
			printf(" -> %s", sym->sec->name);
		printf("\n");
	}
}

bool is_null_sym(struct symbol *sym)
{
	return !strlen(sym->name);
}

bool is_file_sym(struct symbol *sym)
{
	return sym->type == STT_FILE;
}

bool is_local_func_sym(struct symbol *sym)
{
	return sym->bind == STB_LOCAL && sym->type == STT_FUNC;
}

bool is_local_sym(struct symbol *sym)
{
	return sym->bind == STB_LOCAL;
}

void print_strtab(char *buf, size_t size)
{
	size_t i;

	for (i = 0; i < size; i++) {
		if (buf[i] == 0)
			printf("\\0");
		else
			printf("%c",buf[i]);
	}
}

void kpatch_create_shstrtab(struct kpatch_elf *kelf)
{
	struct section *shstrtab, *sec;
	size_t size, offset, len;
	char *buf;

	shstrtab = find_section_by_name(&kelf->sections, ".shstrtab");
	if (!shstrtab)
		ERROR("find_section_by_name");

	/* determine size of string table */
	size = 1; /* for initial NULL terminator */
	list_for_each_entry(sec, &kelf->sections, list)
		size += strlen(sec->name) + 1; /* include NULL terminator */

	/* allocate data buffer */
	buf = malloc(size);
	if (!buf)
		ERROR("malloc");
	memset(buf, 0, size);

	/* populate string table and link with section header */
	offset = 1;
	list_for_each_entry(sec, &kelf->sections, list) {
		len = strlen(sec->name) + 1;
		sec->sh.sh_name = (unsigned int)offset;
		memcpy(buf + offset, sec->name, len);
		offset += len;
	}

	if (offset != size)
		ERROR("shstrtab size mismatch");

	shstrtab->data->d_buf = buf;
	shstrtab->data->d_size = size;

	if (loglevel <= DEBUG) {
		printf("shstrtab: ");
		print_strtab(buf, size);
		printf("\n");

		list_for_each_entry(sec, &kelf->sections, list)
			printf("%s @ shstrtab offset %d\n",
			       sec->name, sec->sh.sh_name);
	}
}

void kpatch_create_strtab(struct kpatch_elf *kelf)
{
	struct section *strtab;
	struct symbol *sym;
	size_t size = 0, offset = 0, len;
	char *buf;

	strtab = find_section_by_name(&kelf->sections, ".strtab");
	if (!strtab)
		ERROR("find_section_by_name");

	/* determine size of string table */
	list_for_each_entry(sym, &kelf->symbols, list) {
		if (sym->type == STT_SECTION)
			continue;
		size += strlen(sym->name) + 1; /* include NULL terminator */
	}

	/* allocate data buffer */
	buf = malloc(size);
	if (!buf)
		ERROR("malloc");
	memset(buf, 0, size);

	/* populate string table and link with section header */
	list_for_each_entry(sym, &kelf->symbols, list) {
		if (sym->type == STT_SECTION) {
			sym->sym.st_name = 0;
			continue;
		}
		len = strlen(sym->name) + 1;
		sym->sym.st_name = (unsigned int)offset;
		memcpy(buf + offset, sym->name, len);
		offset += len;
	}

	if (offset != size)
		ERROR("shstrtab size mismatch");

	strtab->data->d_buf = buf;
	strtab->data->d_size = size;

	if (loglevel <= DEBUG) {
		printf("strtab: ");
		print_strtab(buf, size);
		printf("\n");

		list_for_each_entry(sym, &kelf->symbols, list)
			printf("%s @ strtab offset %d\n",
			       sym->name, sym->sym.st_name);
	}
}

void kpatch_create_symtab(struct kpatch_elf *kelf)
{
	struct section *symtab;
	struct section *strtab;
	struct symbol *sym;
	char *buf;
	size_t size;
	int nr = 0, nr_local = 0;
	unsigned long offset = 0;

	symtab = find_section_by_name(&kelf->sections, ".symtab");
	if (!symtab)
		ERROR("find_section_by_name");

	/* count symbols */
	list_for_each_entry(sym, &kelf->symbols, list)
		nr++;

	/* create new symtab buffer */
	size = nr * symtab->sh.sh_entsize;
	buf = malloc(size);
	if (!buf)
		ERROR("malloc");
	memset(buf, 0, size);

	offset = 0;
	list_for_each_entry(sym, &kelf->symbols, list) {
		memcpy(buf + offset, &sym->sym, symtab->sh.sh_entsize);
		offset += symtab->sh.sh_entsize;

		if (is_local_sym(sym))
			nr_local++;
	}

	symtab->data->d_buf = buf;
	symtab->data->d_size = size;

	/* update symtab section header */
	strtab = find_section_by_name(&kelf->sections, ".strtab");
	if (!strtab)
		ERROR("missing .strtab section");

	symtab->sh.sh_link = strtab->index;
	symtab->sh.sh_info = nr_local;
}

struct section *create_section_pair(struct kpatch_elf *kelf, char *name,
                                    int entsize, int nr)
{
	char *relaname;
	struct section *sec, *relasec;
	int size = entsize * nr;

	relaname = malloc(strlen(name) + strlen(".rela") + 1);
	if (!relaname)
		ERROR("malloc");
	strcpy(relaname, ".rela");
	strcat(relaname, name);

	/* allocate text section resources */
	ALLOC_LINK(sec, &kelf->sections);
	sec->name = name;

	/* set data */
	sec->data = malloc(sizeof(*sec->data));
	if (!sec->data)
		ERROR("malloc");
	sec->data->d_buf = malloc(size);
	if (!sec->data->d_buf)
		ERROR("malloc");
	memset(sec->data->d_buf, 0, size);
	sec->data->d_size = size;
	sec->data->d_type = ELF_T_BYTE;

	/* set section header */
	sec->sh.sh_type = SHT_PROGBITS;
	sec->sh.sh_entsize = entsize;
	sec->sh.sh_addralign = 8;
	sec->sh.sh_flags = SHF_ALLOC;
	sec->sh.sh_size = size;

	/* allocate rela section resources */
	ALLOC_LINK(relasec, &kelf->sections);
	relasec->name = relaname;
	relasec->base = sec;
	INIT_LIST_HEAD(&relasec->relas);

	/* set data, buffers generated by kpatch_rebuild_rela_section_data() */
	relasec->data = malloc(sizeof(*relasec->data));
	if (!relasec->data)
		ERROR("malloc");
	relasec->data->d_type = ELF_T_RELA;

	/* set section header */
	relasec->sh.sh_type = SHT_RELA;
	relasec->sh.sh_entsize = sizeof(GElf_Rela);
	relasec->sh.sh_addralign = 8;

	/* set text rela section pointer */
	sec->rela = relasec;

	return sec;
}

void kpatch_remove_and_free_section(struct kpatch_elf *kelf, char *secname)
{
	struct section *sec, *safesec;
	struct rela *rela, *saferela;

	list_for_each_entry_safe(sec, safesec, &kelf->sections, list) {
		if (strcmp(secname, sec->name))
			continue;

		if (is_rela_section(sec)) {
			list_for_each_entry_safe(rela, saferela, &sec->relas, list) {
				list_del(&rela->list);
				memset(rela, 0, sizeof(*rela));
				free(rela);
			}
		}

		/*
		 * Remove the STT_SECTION symbol from the symtab,
		 * otherwise when we remove the section we'll end up
		 * with UNDEF section symbols in the symtab.
		 */
		if (!is_rela_section(sec) && sec->secsym) {
			list_del(&sec->secsym->list);
			memset(sec->secsym, 0, sizeof(*sec->secsym));
			free(sec->secsym);
		}

		list_del(&sec->list);
		memset(sec, 0, sizeof(*sec));
		free(sec);
	}
}

void kpatch_reindex_elements(struct kpatch_elf *kelf)
{
	struct section *sec;
	struct symbol *sym;
	unsigned int index;

	index = 1; /* elf write function handles NULL section 0 */
	list_for_each_entry(sec, &kelf->sections, list)
		sec->index = index++;

	index = 0;
	list_for_each_entry(sym, &kelf->symbols, list) {
		sym->index = index++;
		if (sym->sec)
			sym->sym.st_shndx = (unsigned short)sym->sec->index;
		else if (sym->sym.st_shndx != SHN_ABS &&
			 sym->sym.st_shndx != SHN_LIVEPATCH)
			sym->sym.st_shndx = SHN_UNDEF;
	}
}

void kpatch_rebuild_rela_section_data(struct section *sec)
{
	struct rela *rela;
	int nr = 0, index = 0;
	GElf_Rela *relas;
	size_t size;

	list_for_each_entry(rela, &sec->relas, list)
		nr++;

	size = nr * sizeof(*relas);
	relas = malloc(size);
	if (!relas)
		ERROR("malloc");

	sec->data->d_buf = relas;
	sec->data->d_size = size;
	/* d_type remains ELF_T_RELA */

	sec->sh.sh_size = size;

	list_for_each_entry(rela, &sec->relas, list) {
		relas[index].r_offset = rela->offset;
		relas[index].r_addend = rela->addend;
		relas[index].r_info = GELF_R_INFO(rela->sym->index, rela->type);
		index++;
	}

	/* sanity check, index should equal nr */
	if (index != nr)
		ERROR("size mismatch in rebuilt rela section");
}

void kpatch_write_output_elf(struct kpatch_elf *kelf, Elf *elf, char *outfile,
			     mode_t mode)
{
	int fd;
	struct section *sec;
	struct section *shstrtab;
	Elf *elfout;
	GElf_Ehdr eh, ehout;
	Elf_Scn *scn;
	Elf_Data *data;
	GElf_Shdr sh;

	fd = creat(outfile, mode);
	if (fd == -1)
		ERROR("creat");

	elfout = elf_begin(fd, ELF_C_WRITE, NULL);
	if (!elfout)
		ERROR("elf_begin");

	if (!gelf_newehdr(elfout, gelf_getclass(elf)))
		ERROR("gelf_newehdr");

	if (!gelf_getehdr(elfout, &ehout))
		ERROR("gelf_getehdr");

	if (!gelf_getehdr(elf, &eh))
		ERROR("gelf_getehdr");

	memset(&ehout, 0, sizeof(ehout));
	ehout.e_ident[EI_DATA] = eh.e_ident[EI_DATA];
	ehout.e_machine = eh.e_machine;
	ehout.e_type = eh.e_type;
	ehout.e_version = EV_CURRENT;

	shstrtab = find_section_by_name(&kelf->sections, ".shstrtab");
	if (!shstrtab)
		ERROR("missing .shstrtab section");

	ehout.e_shstrndx = (unsigned short)shstrtab->index;

	/* add changed sections */
	list_for_each_entry(sec, &kelf->sections, list) {
		scn = elf_newscn(elfout);
		if (!scn)
			ERROR("elf_newscn");

		data = elf_newdata(scn);
		if (!data)
			ERROR("elf_newdata");

		if (!elf_flagdata(data, ELF_C_SET, ELF_F_DIRTY))
			ERROR("elf_flagdata");

		data->d_type = sec->data->d_type;
		data->d_buf = sec->data->d_buf;
		data->d_size = sec->data->d_size;

		if(!gelf_getshdr(scn, &sh))
			ERROR("gelf_getshdr");

		sh = sec->sh;

		if (!gelf_update_shdr(scn, &sh))
			ERROR("gelf_update_shdr");
	}

	if (!gelf_update_ehdr(elfout, &ehout))
		ERROR("gelf_update_ehdr");

	if (elf_update(elfout, ELF_C_WRITE) < 0) {
		printf("%s\n",elf_errmsg(-1));
		ERROR("elf_update");
	}

	elf_end(elfout);
	close(fd);
}

/*
 * While this is a one-shot program without a lot of proper cleanup in case
 * of an error, this function serves a debugging purpose: to break down and
 * zero data structures we shouldn't be accessing anymore.  This should
 * help cause an immediate and obvious issue when a logic error leads to
 * accessing data that is not intended to be accessed past a particular point.
 */
void kpatch_elf_teardown(struct kpatch_elf *kelf)
{
	struct section *sec, *safesec;
	struct symbol *sym, *safesym;
	struct rela *rela, *saferela;

	list_for_each_entry_safe(sec, safesec, &kelf->sections, list) {
		if (sec->twin)
			sec->twin->twin = NULL;
		if (is_rela_section(sec)) {
			list_for_each_entry_safe(rela, saferela, &sec->relas, list) {
				memset(rela, 0, sizeof(*rela));
				free(rela);
			}
		}
		memset(sec, 0, sizeof(*sec));
		free(sec);
	}

	list_for_each_entry_safe(sym, safesym, &kelf->symbols, list) {
		if (sym->twin)
			sym->twin->twin = NULL;
		memset(sym, 0, sizeof(*sym));
		free(sym);
	}

	INIT_LIST_HEAD(&kelf->sections);
	INIT_LIST_HEAD(&kelf->symbols);
}

void kpatch_elf_free(struct kpatch_elf *kelf)
{
	elf_end(kelf->elf);
	close(kelf->fd);
	memset(kelf, 0, sizeof(*kelf));
	free(kelf);
}