/* mod-extract.c: module extractor for signing
 *
 * Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.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.
 */

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdarg.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <elf.h>
#include <asm/byteorder.h>

void extract_elf64(void *buffer, size_t size, Elf64_Ehdr *hdr);
void extract_elf32(void *buffer, size_t size, Elf32_Ehdr *hdr);

struct byteorder {
	uint16_t (*get16)(const uint16_t *);
	uint32_t (*get32)(const uint32_t *);
	uint64_t (*get64)(const uint64_t *);
	void (*set16)(uint16_t *, uint16_t);
	void (*set32)(uint32_t *, uint32_t);
	void (*set64)(uint64_t *, uint64_t);
};

uint16_t get16_le(const uint16_t *p) { return __le16_to_cpu(*p); }
uint32_t get32_le(const uint32_t *p) { return __le32_to_cpu(*p); }
uint64_t get64_le(const uint64_t *p) { return __le64_to_cpu(*p); }
uint16_t get16_be(const uint16_t *p) { return __be16_to_cpu(*p); }
uint32_t get32_be(const uint32_t *p) { return __be32_to_cpu(*p); }
uint64_t get64_be(const uint64_t *p) { return __be64_to_cpu(*p); }

void set16_le(uint16_t *p, uint16_t n) { *p = __cpu_to_le16(n); }
void set32_le(uint32_t *p, uint32_t n) { *p = __cpu_to_le32(n); }
void set64_le(uint64_t *p, uint64_t n) { *p = __cpu_to_le64(n); }
void set16_be(uint16_t *p, uint16_t n) { *p = __cpu_to_be16(n); }
void set32_be(uint32_t *p, uint32_t n) { *p = __cpu_to_be32(n); }
void set64_be(uint64_t *p, uint64_t n) { *p = __cpu_to_be64(n); }

const struct byteorder byteorder_le = {
	get16_le, get32_le, get64_le,
	set16_le, set32_le, set64_le
};
const struct byteorder byteorder_be = {
	get16_be, get32_be, get64_be,
	set16_be, set32_be, set64_be
};
const struct byteorder *order;

uint16_t get16(const uint16_t *p) { return order->get16(p); }
uint32_t get32(const uint32_t *p) { return order->get32(p); }
uint64_t get64(const uint64_t *p) { return order->get64(p); }
void set16(uint16_t *p, uint16_t n) { order->set16(p, n); }
void set32(uint32_t *p, uint32_t n) { order->set32(p, n); }
void set64(uint64_t *p, uint64_t n) { order->set64(p, n); }

FILE *outfd;
uint8_t csum, xcsum;

void write_out(const void *data, size_t size)
{
	const uint8_t *p = data;
	size_t loop;

	for (loop = 0; loop < size; loop++) {
		csum += p[loop];
		xcsum += p[loop];
	}

	if (fwrite(data, 1, size, outfd) != size) {
		perror("write");
		exit(1);
	}
}

#define write_out_val(VAL) write_out(&(VAL), sizeof(VAL))

int is_verbose;

void verbose(const char *fmt, ...) __attribute__((format(printf,1,2)));
void verbose(const char *fmt, ...)
{
	va_list va;

	if (is_verbose) {
		va_start(va, fmt);
		vprintf(fmt, va);
		va_end(va);
	}
}

void usage(void) __attribute__((noreturn));
void usage(void)
{
	fprintf(stderr, "Usage: mod-extract [-v] <modulefile> <extractfile>\n");
	exit(2);
}

/*****************************************************************************/
/*
 *
 */
int main(int argc, char **argv)
{
	struct stat st;
	Elf32_Ehdr *hdr32;
	Elf64_Ehdr *hdr64;
	size_t len;
	void *buffer;
	int fd, be, b64;

	while (argc > 1 && strcmp("-v", argv[1]) == 0) {
		argv++;
		argc--;
		is_verbose++;
	}

	if (argc != 3)
		usage();

	/* map the module into memory */
	fd = open(argv[1], O_RDONLY);
	if (fd < 0) {
		perror("open input");
		exit(1);
	}

	if (fstat(fd, &st) < 0) {
		perror("fstat");
		exit(1);
	}

	len = st.st_size;

	buffer = mmap(NULL, len, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
	if (buffer == MAP_FAILED) {
		perror("mmap");
		exit(1);
	}

	if (close(fd) < 0) {
		perror("close input");
		exit(1);
	}

	/* check it's an ELF object */
	hdr32 = buffer;
	hdr64 = buffer;

	if (hdr32->e_ident[EI_MAG0] != ELFMAG0 ||
	    hdr32->e_ident[EI_MAG1] != ELFMAG1 ||
	    hdr32->e_ident[EI_MAG2] != ELFMAG2 ||
	    hdr32->e_ident[EI_MAG3] != ELFMAG3
	    ) {
		fprintf(stderr, "Module does not appear to be ELF\n");
		exit(3);
	}

	/* determine endianness and word size */
	b64 = (hdr32->e_ident[EI_CLASS] == ELFCLASS64);
	be = (hdr32->e_ident[EI_DATA] == ELFDATA2MSB);
	order = be ? &byteorder_be : &byteorder_le;

	verbose("Module is %s-bit %s-endian\n",
		b64 ? "64" : "32",
		be ? "big" : "little");

	/* open the output file */
	outfd = fopen(argv[2], "w");
	if (!outfd) {
		perror("open output");
		exit(1);
	}

	/* perform the extraction */
	if (b64)
 		extract_elf64(buffer, len, hdr64);
	else
 		extract_elf32(buffer, len, hdr32);

	/* done */
	if (fclose(outfd) == EOF) {
		perror("close output");
		exit(1);
	}

	return 0;

} /* end main() */

/*****************************************************************************/
/*
 * extract a RELA table
 * - need to canonicalise the entries in case section addition/removal has
 *   rearranged the symbol table and the section table
 */
void extract_elf64_rela(const void *buffer, int secix, int targetix,
			const Elf64_Rela *relatab, size_t nrels,
			const Elf64_Sym *symbols, size_t nsyms,
			const Elf64_Shdr *sections, size_t nsects, int *canonmap,
			const char *strings, size_t nstrings,
			const char *sh_name)
{
	struct {
		uint64_t	r_offset;
		uint64_t	r_addend;
		uint64_t	st_value;
		uint64_t	st_size;
		uint32_t	r_type;
		uint16_t	st_shndx;
		uint8_t		st_info;
		uint8_t		st_other;

	} __attribute__((packed)) relocation;

	const Elf64_Sym *symbol;
	size_t loop;

	/* contribute the relevant bits from a join of { RELA, SYMBOL, SECTION } */
	for (loop = 0; loop < nrels; loop++) {
		Elf64_Section st_shndx;
		Elf64_Xword r_info;

		/* decode the relocation */
		r_info = get64(&relatab[loop].r_info);
		relocation.r_offset = relatab[loop].r_offset;
		relocation.r_addend = relatab[loop].r_addend;
		set32(&relocation.r_type, ELF64_R_TYPE(r_info));

		if (ELF64_R_SYM(r_info) >= nsyms) {
			fprintf(stderr, "Invalid symbol ID %lx in relocation %zu\n",
				ELF64_R_SYM(r_info), loop);
			exit(1);
		}

		/* decode the symbol referenced by the relocation */
		symbol = &symbols[ELF64_R_SYM(r_info)];
		relocation.st_info = symbol->st_info;
		relocation.st_other = symbol->st_other;
		relocation.st_value = symbol->st_value;
		relocation.st_size = symbol->st_size;
		relocation.st_shndx = symbol->st_shndx;
		st_shndx = get16(&symbol->st_shndx);

		/* canonicalise the section used by the symbol */
		if (st_shndx > SHN_UNDEF && st_shndx < nsects)
			set16(&relocation.st_shndx, canonmap[st_shndx]);

		write_out_val(relocation);

		/* undefined symbols must be named if referenced */
		if (st_shndx == SHN_UNDEF) {
			const char *name = strings + get32(&symbol->st_name);
			write_out(name, strlen(name) + 1);
		}
	}

	verbose("%02x %4d %s [canon]\n", csum, secix, sh_name);

} /* end extract_elf64_rela() */

/*****************************************************************************/
/*
 * extract a REL table
 * - need to canonicalise the entries in case section addition/removal has
 *   rearranged the symbol table and the section table
 */
void extract_elf64_rel(const void *buffer, int secix, int targetix,
		       const Elf64_Rel *relatab, size_t nrels,
		       const Elf64_Sym *symbols, size_t nsyms,
		       const Elf64_Shdr *sections, size_t nsects, int *canonmap,
		       const char *strings, size_t nstrings,
		       const char *sh_name)
{
	struct {
		uint64_t	r_offset;
		uint64_t	st_value;
		uint64_t	st_size;
		uint32_t	r_type;
		uint16_t	st_shndx;
		uint8_t		st_info;
		uint8_t		st_other;

	} __attribute__((packed)) relocation;

	const Elf64_Sym *symbol;
	size_t loop;

	/* contribute the relevant bits from a join of { RELA, SYMBOL, SECTION } */
	for (loop = 0; loop < nrels; loop++) {
		Elf64_Section st_shndx;
		Elf64_Xword r_info;

		/* decode the relocation */
		r_info = get64(&relatab[loop].r_info);
		relocation.r_offset = relatab[loop].r_offset;
		set32(&relocation.r_type, ELF64_R_TYPE(r_info));

		if (ELF64_R_SYM(r_info) >= nsyms) {
			fprintf(stderr, "Invalid symbol ID %lx in relocation %zi\n",
				ELF64_R_SYM(r_info), loop);
			exit(1);
		}

		/* decode the symbol referenced by the relocation */
		symbol = &symbols[ELF64_R_SYM(r_info)];
		relocation.st_info = symbol->st_info;
		relocation.st_other = symbol->st_other;
		relocation.st_value = symbol->st_value;
		relocation.st_size = symbol->st_size;
		relocation.st_shndx = symbol->st_shndx;
		st_shndx = get16(&symbol->st_shndx);

		/* canonicalise the section used by the symbol */
		if (st_shndx > SHN_UNDEF && st_shndx < nsects)
			set16(&relocation.st_shndx, canonmap[st_shndx]);

		write_out_val(relocation);

		/* undefined symbols must be named if referenced */
		if (st_shndx == SHN_UNDEF) {
			const char *name = strings + get32(&symbol->st_name);
			write_out(name, strlen(name) + 1);
		}
	}

	verbose("%02x %4d %s [canon]\n", csum, secix, sh_name);

} /* end extract_elf64_rel() */

/*****************************************************************************/
/*
 * extract the data from a 64-bit module
 */
void extract_elf64(void *buffer, size_t len, Elf64_Ehdr *hdr)
{
	const Elf64_Sym *symbols;
	Elf64_Shdr *sections;
	const char *secstrings, *strings;
	size_t nsyms, nstrings;
	int loop, shnum, *canonlist, *canonmap, canon, changed, tmp;

	sections = buffer + get64(&hdr->e_shoff);
	secstrings = buffer + get64(&sections[get16(&hdr->e_shstrndx)].sh_offset);
	shnum = get16(&hdr->e_shnum);

	/* find the symbol table and the string table and produce a list of
	 * index numbers of sections that contribute to the kernel's module
	 * image
	 */
	canonlist = calloc(sizeof(int), shnum * 2);
	if (!canonlist) {
		perror("calloc");
		exit(1);
	}
	canonmap = canonlist + shnum;
	canon = 0;

	symbols = NULL;
	strings = NULL;

	for (loop = 1; loop < shnum; loop++) {
		const char *sh_name = secstrings + get32(&sections[loop].sh_name);
		Elf64_Word  sh_type	= get32(&sections[loop].sh_type);
		Elf64_Xword sh_size	= get64(&sections[loop].sh_size);
		Elf64_Xword sh_flags	= get64(&sections[loop].sh_flags);
		Elf64_Off   sh_offset	= get64(&sections[loop].sh_offset);
		void *data = buffer + sh_offset;

		/* quick sanity check */
		if (sh_type != SHT_NOBITS && len < sh_offset + sh_size) {
			fprintf(stderr, "Section goes beyond EOF\n");
			exit(3);
		}

		/* we only need to canonicalise allocatable sections */
		if (sh_flags & SHF_ALLOC)
			canonlist[canon++] = loop;

		/* keep track of certain special sections */
		switch (sh_type) {
		case SHT_SYMTAB:
			if (strcmp(sh_name, ".symtab") == 0) {
				symbols = data;
				nsyms = sh_size / sizeof(Elf64_Sym);
			}
			break;

		case SHT_STRTAB:
			if (strcmp(sh_name, ".strtab") == 0) {
				strings = data;
				nstrings = sh_size;
			}
			break;

		default:
			break;
		}
	}

	if (!symbols) {
		fprintf(stderr, "Couldn't locate symbol table\n");
		exit(3);
	}

	if (!strings) {
		fprintf(stderr, "Couldn't locate strings table\n");
		exit(3);
	}

	/* canonicalise the index numbers of the contributing section */
	do {
		changed = 0;

		for (loop = 0; loop < canon - 1; loop++) {
			const char *x = secstrings + get32(&sections[canonlist[loop + 0]].sh_name);
			const char *y = secstrings + get32(&sections[canonlist[loop + 1]].sh_name);
			if (strcmp(x, y) > 0) {
				tmp = canonlist[loop + 0];
				canonlist[loop + 0] = canonlist[loop + 1];
				canonlist[loop + 1] = tmp;
				changed = 1;
			}
		}

	} while(changed);

	for (loop = 0; loop < canon; loop++)
		canonmap[canonlist[loop]] = loop + 1;

	if (is_verbose > 1) {
		printf("\nSection canonicalisation map:\n");
		for (loop = 1; loop < shnum; loop++) {
			const char *x = secstrings + get32(&sections[loop].sh_name);
			printf("%4d %s\n", canonmap[loop], x);
		}

		printf("\nAllocated section list in canonical order:\n");
		for (loop = 0; loop < canon; loop++) {
			const char *x = secstrings + get32(&sections[canonlist[loop]].sh_name);
			printf("%4d %s\n", canonlist[loop], x);
		}
	}

	memset(canonlist, 0, sizeof(int) * shnum);

	/* iterate through the section table looking for sections we want to
	 * contribute to the signature */
	verbose("\n");
	verbose("FILE POS CS SECT NAME\n");
	verbose("======== == ==== ==============================\n");

	for (loop = 1; loop < shnum; loop++) {
		const char *sh_name = secstrings + get32(&sections[loop].sh_name);
		Elf64_Word  sh_type	= get32(&sections[loop].sh_type);
		Elf64_Xword sh_size	= get64(&sections[loop].sh_size);
		Elf64_Xword sh_flags	= get64(&sections[loop].sh_flags);
		Elf64_Word  sh_info	= get32(&sections[loop].sh_info);
		Elf64_Off   sh_offset	= get64(&sections[loop].sh_offset);
		void *data = buffer + sh_offset;

		csum = 0;

		/* include canonicalised relocation sections */
		if (sh_type == SHT_REL || sh_type == SHT_RELA) {
			if (sh_info <= 0 && sh_info >= hdr->e_shnum) {
				fprintf(stderr,
					"Invalid ELF - REL/RELA sh_info does"
					" not refer to a valid section\n");
				exit(3);
			}

			if (canonlist[sh_info]) {
				Elf32_Word xsh_info;

				verbose("%08lx ", ftell(outfd));

				set32(&xsh_info, canonmap[sh_info]);

				/* write out selected portions of the section
				 * header */
				write_out(sh_name, strlen(sh_name));
				write_out_val(sections[loop].sh_type);
				write_out_val(sections[loop].sh_flags);
				write_out_val(sections[loop].sh_size);
				write_out_val(sections[loop].sh_addralign);
				write_out_val(xsh_info);

				if (sh_type == SHT_RELA)
					extract_elf64_rela(buffer, loop, sh_info,
							   data, sh_size / sizeof(Elf64_Rela),
							   symbols, nsyms,
							   sections, shnum, canonmap,
							   strings, nstrings,
							   sh_name);
				else
					extract_elf64_rel(buffer, loop, sh_info,
							  data, sh_size / sizeof(Elf64_Rel),
							  symbols, nsyms,
							  sections, shnum, canonmap,
							  strings, nstrings,
							  sh_name);
			}

			continue;
		}

		/* include allocatable loadable sections */
		if (sh_type != SHT_NOBITS && sh_flags & SHF_ALLOC)
			goto include_section;

		/* not this section */
		continue;

	include_section:
		verbose("%08lx ", ftell(outfd));

		/* write out selected portions of the section header */
		write_out(sh_name, strlen(sh_name));
		write_out_val(sections[loop].sh_type);
		write_out_val(sections[loop].sh_flags);
		write_out_val(sections[loop].sh_size);
		write_out_val(sections[loop].sh_addralign);

		/* write out the section data */
		write_out(data, sh_size);

		verbose("%02x %4d %s\n", csum, loop, sh_name);

		/* note the section has been written */
		canonlist[loop] = 1;
	}

	verbose("%08lx         (%lu bytes csum 0x%02x)\n",
		ftell(outfd), ftell(outfd), xcsum);

} /* end extract_elf64() */

/*****************************************************************************/
/*
 * extract a RELA table
 * - need to canonicalise the entries in case section addition/removal has
 *   rearranged the symbol table and the section table
 */
void extract_elf32_rela(const void *buffer, int secix, int targetix,
			const Elf32_Rela *relatab, size_t nrels,
			const Elf32_Sym *symbols, size_t nsyms,
			const Elf32_Shdr *sections, size_t nsects, int *canonmap,
			const char *strings, size_t nstrings,
			const char *sh_name)
{
	struct {
		uint32_t	r_offset;
		uint32_t	r_addend;
		uint32_t	st_value;
		uint32_t	st_size;
		uint16_t	st_shndx;
		uint8_t		r_type;
		uint8_t		st_info;
		uint8_t		st_other;

	} __attribute__((packed)) relocation;

	const Elf32_Sym *symbol;
	size_t loop;

	/* contribute the relevant bits from a join of { RELA, SYMBOL, SECTION } */
	for (loop = 0; loop < nrels; loop++) {
		Elf32_Section st_shndx;
		Elf32_Word r_info;

		/* decode the relocation */
		r_info = get32(&relatab[loop].r_info);
		relocation.r_offset = relatab[loop].r_offset;
		relocation.r_addend = relatab[loop].r_addend;
		relocation.r_type = ELF32_R_TYPE(r_info);

		if (ELF32_R_SYM(r_info) >= nsyms) {
			fprintf(stderr, "Invalid symbol ID %x in relocation %zu\n",
				ELF32_R_SYM(r_info), loop);
			exit(1);
		}

		/* decode the symbol referenced by the relocation */
		symbol = &symbols[ELF32_R_SYM(r_info)];
		relocation.st_info = symbol->st_info;
		relocation.st_other = symbol->st_other;
		relocation.st_value = symbol->st_value;
		relocation.st_size = symbol->st_size;
		relocation.st_shndx = symbol->st_shndx;
		st_shndx = get16(&symbol->st_shndx);

		/* canonicalise the section used by the symbol */
		if (st_shndx > SHN_UNDEF && st_shndx < nsects)
			set16(&relocation.st_shndx, canonmap[st_shndx]);

		write_out_val(relocation);

		/* undefined symbols must be named if referenced */
		if (st_shndx == SHN_UNDEF) {
			const char *name = strings + get32(&symbol->st_name);
			write_out(name, strlen(name) + 1);
		}
	}

	verbose("%02x %4d %s [canon]\n", csum, secix, sh_name);

} /* end extract_elf32_rela() */

/*****************************************************************************/
/*
 * extract a REL table
 * - need to canonicalise the entries in case section addition/removal has
 *   rearranged the symbol table and the section table
 */
void extract_elf32_rel(const void *buffer, int secix, int targetix,
		       const Elf32_Rel *relatab, size_t nrels,
		       const Elf32_Sym *symbols, size_t nsyms,
		       const Elf32_Shdr *sections, size_t nsects, int *canonmap,
		       const char *strings, size_t nstrings,
		       const char *sh_name)
{
	struct {
		uint32_t	r_offset;
		uint32_t	st_value;
		uint32_t	st_size;
		uint16_t	st_shndx;
		uint8_t		r_type;
		uint8_t		st_info;
		uint8_t		st_other;

	} __attribute__((packed)) relocation;

	const Elf32_Sym *symbol;
	size_t loop;

	/* contribute the relevant bits from a join of { RELA, SYMBOL, SECTION } */
	for (loop = 0; loop < nrels; loop++) {
		Elf32_Section st_shndx;
		Elf32_Word r_info;

		/* decode the relocation */
		r_info = get32(&relatab[loop].r_info);
		relocation.r_offset = relatab[loop].r_offset;
		relocation.r_type = ELF32_R_TYPE(r_info);

		if (ELF32_R_SYM(r_info) >= nsyms) {
			fprintf(stderr, "Invalid symbol ID %x in relocation %zu\n",
				ELF32_R_SYM(r_info), loop);
			exit(1);
		}

		/* decode the symbol referenced by the relocation */
		symbol = &symbols[ELF32_R_SYM(r_info)];
		relocation.st_info = symbol->st_info;
		relocation.st_other = symbol->st_other;
		relocation.st_value = symbol->st_value;
		relocation.st_size = symbol->st_size;
		relocation.st_shndx = symbol->st_shndx;
		st_shndx = get16(&symbol->st_shndx);

		/* canonicalise the section used by the symbol */
		if (st_shndx > SHN_UNDEF && st_shndx < nsects)
			set16(&relocation.st_shndx, canonmap[st_shndx]);
		
		write_out_val(relocation);

		/* undefined symbols must be named if referenced */
		if (st_shndx == SHN_UNDEF) {
			const char *name = strings + get32(&symbol->st_name);
			write_out(name, strlen(name) + 1);
		}
	}

	verbose("%02x %4d %s [canon]\n", csum, secix, sh_name);

} /* end extract_elf32_rel() */

/*****************************************************************************/
/*
 * extract the data from a 32-bit module
 */
void extract_elf32(void *buffer, size_t len, Elf32_Ehdr *hdr)
{
	const Elf32_Sym *symbols;
	Elf32_Shdr *sections;
	const char *secstrings, *strings;
	size_t nsyms, nstrings;
	int loop, shnum, *canonlist, *canonmap, canon, changed, tmp;

	sections = buffer + get32(&hdr->e_shoff);
	secstrings = buffer + get32(&sections[get16(&hdr->e_shstrndx)].sh_offset);
	shnum = get16(&hdr->e_shnum);

	/* find the symbol table and the string table and produce a list of
	 * index numbers of sections that contribute to the kernel's module
	 * image
	 */
	canonlist = calloc(sizeof(int), shnum * 2);
	if (!canonlist) {
		perror("calloc");
		exit(1);
	}
	canonmap = canonlist + shnum;
	canon = 0;

	symbols = NULL;
	strings = NULL;

	for (loop = 1; loop < shnum; loop++) {
		const char *sh_name = secstrings + get32(&sections[loop].sh_name);
		Elf32_Word  sh_type	= get32(&sections[loop].sh_type);
		Elf32_Xword sh_size	= get32(&sections[loop].sh_size);
		Elf32_Xword sh_flags	= get32(&sections[loop].sh_flags);
		Elf32_Off   sh_offset	= get32(&sections[loop].sh_offset);
		void *data = buffer + sh_offset;

		/* quick sanity check */
		if (sh_type != SHT_NOBITS && len < sh_offset + sh_size) {
			fprintf(stderr, "Section goes beyond EOF\n");
			exit(3);
		}

		/* we only need to canonicalise allocatable sections */
		if (sh_flags & SHF_ALLOC)
			canonlist[canon++] = loop;

		/* keep track of certain special sections */
		switch (sh_type) {
		case SHT_SYMTAB:
			if (strcmp(sh_name, ".symtab") == 0) {
				symbols = data;
				nsyms = sh_size / sizeof(Elf32_Sym);
			}
			break;

		case SHT_STRTAB:
			if (strcmp(sh_name, ".strtab") == 0) {
				strings = data;
				nstrings = sh_size;
			}
			break;

		default:
			break;
		}
	}

	if (!symbols) {
		fprintf(stderr, "Couldn't locate symbol table\n");
		exit(3);
	}

	if (!strings) {
		fprintf(stderr, "Couldn't locate strings table\n");
		exit(3);
	}

	/* canonicalise the index numbers of the contributing section */
	do {
		changed = 0;

		for (loop = 0; loop < canon - 1; loop++) {
			const char *x = secstrings + get32(&sections[canonlist[loop + 0]].sh_name);
			const char *y = secstrings + get32(&sections[canonlist[loop + 1]].sh_name);
			if (strcmp(x, y) > 0) {
				tmp = canonlist[loop + 0];
				canonlist[loop + 0] = canonlist[loop + 1];
				canonlist[loop + 1] = tmp;
				changed = 1;
			}
		}

	} while(changed);

	for (loop = 0; loop < canon; loop++)
		canonmap[canonlist[loop]] = loop + 1;

	if (is_verbose > 1) {
		printf("\nSection canonicalisation map:\n");
		for (loop = 1; loop < shnum; loop++) {
			const char *x = secstrings + get32(&sections[loop].sh_name);
			printf("%4d %s\n", canonmap[loop], x);
		}

		printf("\nAllocated section list in canonical order:\n");
		for (loop = 0; loop < canon; loop++) {
			const char *x = secstrings + get32(&sections[canonlist[loop]].sh_name);
			printf("%4d %s\n", canonlist[loop], x);
		}
	}

	memset(canonlist, 0, sizeof(int) * shnum);

	/* iterate through the section table looking for sections we want to
	 * contribute to the signature */
	verbose("\n");
	verbose("FILE POS CS SECT NAME\n");
	verbose("======== == ==== ==============================\n");

	for (loop = 1; loop < shnum; loop++) {
		const char *sh_name = secstrings + get32(&sections[loop].sh_name);
		Elf32_Word  sh_type	= get32(&sections[loop].sh_type);
		Elf32_Xword sh_size	= get32(&sections[loop].sh_size);
		Elf32_Xword sh_flags	= get32(&sections[loop].sh_flags);
		Elf32_Word  sh_info	= get32(&sections[loop].sh_info);
		Elf32_Off   sh_offset	= get32(&sections[loop].sh_offset);
		void *data = buffer + sh_offset;

		csum = 0;

		/* quick sanity check */
		if (sh_type != SHT_NOBITS && len < sh_offset + sh_size) {
			fprintf(stderr, "section goes beyond EOF\n");
			exit(3);
		}

		/* include canonicalised relocation sections */
		if (sh_type == SHT_REL || sh_type == SHT_RELA) {
			if (sh_info <= 0 && sh_info >= hdr->e_shnum) {
				fprintf(stderr,
					"Invalid ELF - REL/RELA sh_info does"
					" not refer to a valid section\n");
				exit(3);
			}

			if (canonlist[sh_info]) {
				Elf32_Word xsh_info;

				verbose("%08lx ", ftell(outfd));

				set32(&xsh_info, canonmap[sh_info]);

				/* write out selected portions of the section header */
				write_out(sh_name, strlen(sh_name));
				write_out_val(sections[loop].sh_type);
				write_out_val(sections[loop].sh_flags);
				write_out_val(sections[loop].sh_size);
				write_out_val(sections[loop].sh_addralign);
				write_out_val(xsh_info);

				if (sh_type == SHT_RELA)
					extract_elf32_rela(buffer, loop, sh_info,
							   data, sh_size / sizeof(Elf32_Rela),
							   symbols, nsyms,
							   sections, shnum, canonmap,
							   strings, nstrings,
							   sh_name);
				else
					extract_elf32_rel(buffer, loop, sh_info,
							  data, sh_size / sizeof(Elf32_Rel),
							  symbols, nsyms,
							  sections, shnum, canonmap,
							  strings, nstrings,
							  sh_name);
			}

			continue;
		}

		/* include allocatable loadable sections */
		if (sh_type != SHT_NOBITS && sh_flags & SHF_ALLOC)
			goto include_section;

		/* not this section */
		continue;

	include_section:
		verbose("%08lx ", ftell(outfd));

		/* write out selected portions of the section header */
		write_out(sh_name, strlen(sh_name));
		write_out_val(sections[loop].sh_type);
		write_out_val(sections[loop].sh_flags);
		write_out_val(sections[loop].sh_size);
		write_out_val(sections[loop].sh_addralign);

		/* write out the section data */
		write_out(data, sh_size);

		verbose("%02x %4d %s\n", csum, loop, sh_name);

		/* note the section has been written */
		canonlist[loop] = 1;
	}

	verbose("%08lx         (%lu bytes csum 0x%02x)\n",
		ftell(outfd), ftell(outfd), xcsum);

} /* end extract_elf32() */