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malloc(x * y) -> calloc(x, y) from adobriyan AT gmail.com, with tweaks
suggested by kjell@; ok otto@ pat@ millert@ jaredy@

/* $OpenBSD: elf2aout.c,v 1.6 2006/04/02 21:38:56 djm Exp $	 */

/*
 * Copyright (c) 1995
 *	Ted Lemon (hereinafter referred to as the author)
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <elf_abi.h>
#include <machine/elf_abi.h>
#include <stdio.h>
#include <a.out.h>
#include <errno.h>
#include <string.h>
#include <limits.h>

#define SHN_MIPS_ACOMMON 0xfff0

extern char    *__progname;

struct sect {
	unsigned long   vaddr;
	unsigned long   len;
};
int             phcmp();
char           *saveRead(int file, off_t offset, off_t len, char *name);
int             copy(int, int, off_t, off_t);
int             translate_syms(int, int, off_t, off_t, off_t, off_t);
int            *symTypeTable;

/* Symbol table entry... */
struct sym {
	unsigned long   name;	/* Index into strtab of symbol name. */
	unsigned long   value;	/* Section offset, virt addr or common align. */
	unsigned long   size;	/* Size of object referenced. */
	unsigned        type:4;	/* Symbol type (e.g., function, data)... */
	unsigned        binding:4;	/* Symbol binding (e.g., global,
					 * local)... */
	unsigned char   other;	/* Unused. */
	unsigned short  shndx;	/* Section containing symbol. */
};

struct phdr {
	unsigned long   type;	/* Segment type... */
	unsigned long   offset;	/* File offset... */
	unsigned long   vaddr;	/* Virtual address... */
	unsigned long   paddr;	/* Physical address... */
	unsigned long   filesz;	/* Size of segment in file... */
	unsigned long   memsz;	/* Size of segment in memory... */
	unsigned long   flags;	/* Segment flags... */
	unsigned long   align;	/* Alighment, file and memory... */
};

int
main(int argc, char *argv[])
{
	Elf32_Ehdr      ex;
	Elf32_Phdr     *ph;
	Elf32_Shdr     *sh;
	struct sym     *symtab;
	char           *shstrtab;
	int             strtabix, symtabix;
	int             i;
	struct sect     text, data, bss;
	struct exec     aex;
	int             infile, outfile;
	unsigned long   cur_vma = ULONG_MAX;
	int             symflag = 0;

	text.len = data.len = bss.len = 0;
	text.vaddr = data.vaddr = bss.vaddr = 0;

	/* Check args... */
	if (argc < 3 || argc > 4) {
usage:
		fprintf(stderr,
		    "usage: %s elf a.out\n", __progname);
		exit(1);
	}
	/* Try the input file... */
	if ((infile = open(argv[1], O_RDONLY)) < 0) {
		fprintf(stderr, "Can't open %s for read: %s\n",
			argv[1], strerror(errno));
		exit(1);
	}
	/* Read the header, which is at the beginning of the file... */
	i = read(infile, &ex, sizeof ex);
	if (i != sizeof ex) {
		fprintf(stderr, "ex: %s: %s.\n",
		    argv[1], i ? strerror(errno) : "End of file reached");
		exit(1);
	}
	/* Read the program headers... */
	ph = (Elf32_Phdr *) saveRead(infile, ex.e_phoff,
				     ex.e_phnum * sizeof(Elf32_Phdr), "ph");
	/* Read the section headers... */
	sh = (Elf32_Shdr *) saveRead(infile, ex.e_shoff,
				     ex.e_shnum * sizeof(Elf32_Shdr), "sh");
	/* Read in the section string table. */
	shstrtab = saveRead(infile, sh[ex.e_shstrndx].sh_offset,
			    sh[ex.e_shstrndx].sh_size, "shstrtab");

	/*
	 * Find space for a table matching ELF section indices to a.out
	 * symbol types.
	 */
	symTypeTable = calloc(ex.e_shnum, sizeof(int));
	if (!symTypeTable) {
		fprintf(stderr, "symTypeTable: can't allocate.\n");
		exit(1);
	}

	/*
	 * Look for the symbol table and string table... Also map section
	 * indices to symbol types for a.out
	 */
	for (i = 0; i < ex.e_shnum; i++) {
		char           *name = shstrtab + sh[i].sh_name;
		if (!strcmp(name, ".symtab"))
			symtabix = i;
		else if (!strcmp(name, ".strtab"))
			strtabix = i;
		else if (!strcmp(name, ".text") || !strcmp(name, ".rodata"))
			symTypeTable[i] = N_TEXT;
		else if (!strcmp(name, ".data") || !strcmp(name, ".sdata") ||
			 !strcmp(name, ".lit4") || !strcmp(name, ".lit8"))
			symTypeTable[i] = N_DATA;
		else if (!strcmp(name, ".bss") || !strcmp(name, ".sbss"))
			symTypeTable[i] = N_BSS;
	}

	/*
	 * Figure out if we can cram the program header into an a.out
	 * header... Basically, we can't handle anything but loadable
	 * segments, but we can ignore some kinds of segments.   We can't
	 * handle holes in the address space, and we handle start addresses
	 * other than 0x1000 by hoping that the loader will know where to
	 * load - a.out doesn't have an explicit load address.   Segments may
	 * be out of order, so we sort them first.
	 */
	qsort(ph, ex.e_phnum, sizeof(Elf32_Phdr), phcmp);
	for (i = 0; i < ex.e_phnum; i++) {
		/* Section types we can ignore... */
		if (ph[i].p_type == PT_NULL || ph[i].p_type == PT_NOTE ||
		 ph[i].p_type == PT_PHDR || ph[i].p_type == PT_MIPS_REGINFO)
			continue;
		/* Section types we can't handle... */
		else if (ph[i].p_type != PT_LOAD) {
			fprintf(stderr,
			    "Program header %d type %d can't be converted.\n",
			    i, ph[i].p_type);
			exit(1);
		}
		/* Writable (data) segment? */
		if (ph[i].p_flags & PF_W) {
			struct sect     ndata, nbss;

			ndata.vaddr = ph[i].p_vaddr;
			ndata.len = ph[i].p_filesz;
			nbss.vaddr = ph[i].p_vaddr + ph[i].p_filesz;
			nbss.len = ph[i].p_memsz - ph[i].p_filesz;

			combine(&data, &ndata, 0);
			combine(&bss, &nbss, 1);
		} else {
			struct sect     ntxt;

			ntxt.vaddr = ph[i].p_vaddr;
			ntxt.len = ph[i].p_filesz;

			combine(&text, &ntxt);
		}
		/* Remember the lowest segment start address. */
		if (ph[i].p_vaddr < cur_vma)
			cur_vma = ph[i].p_vaddr;
	}

	/* Sections must be in order to be converted... */
	if (text.vaddr > data.vaddr || data.vaddr > bss.vaddr ||
	    text.vaddr + text.len > data.vaddr || data.vaddr + data.len > bss.vaddr) {
		fprintf(stderr, "Sections ordering prevents a.out conversion.\n");
		exit(1);
	}
	/*
	 * If there's a data section but no text section, then the loader
	 * combined everything into one section.   That needs to be the text
	 * section, so just make the data section zero length following text.
	 */
	if (data.len && !text.len) {
		text = data;
		data.vaddr = text.vaddr + text.len;
		data.len = 0;
	}
	/*
	 * If there is a gap between text and data, we'll fill it when we
	 * copy the data, so update the length of the text segment as
	 * represented in a.out to reflect that, since a.out doesn't allow
	 * gaps in the program address space.
	 */
	if (text.vaddr + text.len < data.vaddr)
		text.len = data.vaddr - text.vaddr;

	/* We now have enough information to cons up an a.out header... */
	aex.a_midmag = htonl((symflag << 26) | (MID_PMAX << 16) | OMAGIC);
	aex.a_text = text.len;
	aex.a_data = data.len;
	aex.a_bss = bss.len;
	aex.a_entry = ex.e_entry;
	aex.a_syms = (sizeof(struct nlist) *
		      (symtabix != -1
		       ? sh[symtabix].sh_size / sizeof(struct sym) : 0));
	aex.a_trsize = 0;
	aex.a_drsize = 0;

	/* Make the output file... */
	if ((outfile = open(argv[2], O_WRONLY | O_CREAT, 0777)) < 0) {
		fprintf(stderr, "Unable to create %s: %s\n", argv[2], strerror(errno));
		exit(1);
	}
	/* Write the header... */
	i = write(outfile, &aex, sizeof aex);
	if (i != sizeof aex) {
		perror("aex: write");
		exit(1);
	}
	/*
	 * Copy the loadable sections.   Zero-fill any gaps less than 64k;
	 * complain about any zero-filling, and die if we're asked to
	 * zero-fill more than 64k.
	 */
	for (i = 0; i < ex.e_phnum; i++) {
		/*
		 * Unprocessable sections were handled above, so just verify
		 * that the section can be loaded before copying.
		 */
		if (ph[i].p_type == PT_LOAD && ph[i].p_filesz) {
			if (cur_vma != ph[i].p_vaddr) {
				unsigned long   gap = ph[i].p_vaddr - cur_vma;
				char obuf[1024];

				if (gap > 65536) {
					fprintf(stderr,
					    "Intersegment gap (%d bytes) too large.\n",
					    gap);
					exit(1);
				}
				fprintf(stderr,
				    "Warning: %d byte intersegment gap.\n", gap);
				memset(obuf, 0, sizeof obuf);
				while (gap) {
					int count = write(outfile, obuf,
					    (gap > sizeof obuf ? sizeof obuf : gap));
					if (count < 0) {
						fprintf(stderr,
						    "Error writing gap: %s\n",
						    strerror(errno));
						exit(1);
					}
					gap -= count;
				}
			}
			copy(outfile, infile, ph[i].p_offset, ph[i].p_filesz);
			cur_vma = ph[i].p_vaddr + ph[i].p_filesz;
		}
	}

	/* Copy and translate the symbol table... */
	translate_syms(outfile, infile, sh[symtabix].sh_offset,
		       sh[symtabix].sh_size,
		       sh[strtabix].sh_offset, sh[strtabix].sh_size);

	/* Looks like we won... */
	exit(0);
}

/*
 * translate_syms (out, in, offset, size)
 * 
 * Read the ELF symbol table from in at offset; translate it into a.out nlist
 * format and write it to out.
 */

translate_syms(int out, int in, off_t symoff, off_t symsize, off_t stroff,
    off_t strsize)
{
#define SYMS_PER_PASS	64
	struct sym      inbuf[64];
	struct nlist    outbuf[64];
	int             i, remaining, cur;
	char           *oldstrings;
	char           *newstrings, *nsp;
	int             newstringsize;

	/* Zero the unused fields in the output buffer.. */
	memset(outbuf, 0, sizeof outbuf);

	/* Find number of symbols to process... */
	remaining = symsize / sizeof(struct sym);

	/* Suck in the old string table... */
	oldstrings = saveRead(in, stroff, strsize, "string table");

	/*
	 * Allocate space for the new one.   XXX We make the wild assumption
	 * that no two symbol table entries will point at the same place in
	 * the string table - if that assumption is bad, this could easily
	 * blow up.
	 */
	newstringsize = strsize + remaining;
	newstrings = (char *) malloc(newstringsize);
	if (!newstrings) {
		fprintf(stderr, "No memory for new string table!\n");
		exit(1);
	}
	/* Initialize the table pointer... */
	nsp = newstrings;

	/* Go to the start of the ELF symbol table... */
	if (lseek(in, symoff, SEEK_SET) < 0) {
		perror("translate_syms: lseek");
		exit(1);
	}
	/* Translate and copy symbols... */
	while (remaining) {
		cur = remaining;
		if (cur > SYMS_PER_PASS)
			cur = SYMS_PER_PASS;
		remaining -= cur;
		if ((i = read(in, inbuf, cur * sizeof(struct sym)))
		    != cur * sizeof(struct sym)) {
			if (i < 0)
				perror("translate_syms");
			else
				fprintf(stderr,
				    "translate_syms: premature end of file.\n");
			exit(1);
		}
		/* Do the translation... */
		for (i = 0; i < cur; i++) {
			/*
			 * Copy the symbol into the new table, but prepend an
			 * underscore.
			 */
			*nsp = '_';
			strcpy(nsp + 1, oldstrings + inbuf[i].name);
			outbuf[i].n_un.n_strx = nsp - newstrings + 4;
			nsp += strlen(nsp) + 1;

			/*
			 * Convert ELF symbol type/section/etc info into
			 * a.out type info.
			 */
			if (inbuf[i].type == STT_FILE)
				outbuf[i].n_type = N_FN;
			else if (inbuf[i].shndx == SHN_UNDEF)
				outbuf[i].n_type = N_UNDF;
			else if (inbuf[i].shndx == SHN_ABS)
				outbuf[i].n_type = N_ABS;
			else if (inbuf[i].shndx == SHN_COMMON ||
				 inbuf[i].shndx == SHN_MIPS_ACOMMON)
				outbuf[i].n_type = N_COMM;
			else
				outbuf[i].n_type = symTypeTable[inbuf[i].shndx];
			if (inbuf[i].binding == STB_GLOBAL)
				outbuf[i].n_type |= N_EXT;
			/* Symbol values in executables should be compatible. */
			outbuf[i].n_value = inbuf[i].value;
		}
		/* Write out the symbols... */
		if ((i = write(out, outbuf, cur * sizeof(struct nlist)))
		    != cur * sizeof(struct nlist)) {
			fprintf(stderr, "translate_syms: write: %s\n", strerror(errno));
			exit(1);
		}
	}
	/* Write out the string table length... */
	if (write(out, &newstringsize, sizeof newstringsize)
	    != sizeof newstringsize) {
		fprintf(stderr,
		    "translate_syms: newstringsize: %s\n", strerror(errno));
		exit(1);
	}
	/* Write out the string table... */
	if (write(out, newstrings, newstringsize) != newstringsize) {
		fprintf(stderr, "translate_syms: newstrings: %s\n", strerror(errno));
		exit(1);
	}
}

copy(int out, int in, off_t offset, off_t size)
{
	char ibuf[4096];
	int  remaining, cur, count;

	/* Go to the start of the ELF symbol table... */
	if (lseek(in, offset, SEEK_SET) < 0) {
		perror("copy: lseek");
		exit(1);
	}
	remaining = size;
	while (remaining) {
		cur = remaining;
		if (cur > sizeof ibuf)
			cur = sizeof ibuf;
		remaining -= cur;
		if ((count = read(in, ibuf, cur)) != cur) {
			fprintf(stderr, "copy: read: %s\n",
			 count ? strerror(errno) : "premature end of file");
			exit(1);
		}
		if ((count = write(out, ibuf, cur)) != cur) {
			perror("copy: write");
			exit(1);
		}
	}
}

/*
 * Combine two segments, which must be contiguous.   If pad is true, it's
 * okay for there to be padding between.
 */
combine(struct sect * base, struct sect * new, int pad)
{
	if (!base->len)
		*base = *new;
	else if (new->len) {
		if (base->vaddr + base->len != new->vaddr) {
			if (pad)
				base->len = new->vaddr - base->vaddr;
			else {
				fprintf(stderr,
				"Non-contiguous data can't be converted.\n");
				exit(1);
			}
		}
		base->len += new->len;
	}
}

phcmp(struct phdr * h1, struct phdr * h2)
{
	if (h1->vaddr > h2->vaddr)
		return 1;
	else if (h1->vaddr < h2->vaddr)
		return -1;
	else
		return 0;
}

char           *
saveRead(int file, off_t offset, off_t len, char *name)
{
	char           *tmp;
	int             count;
	off_t           off;

	if ((off = lseek(file, offset, SEEK_SET)) < 0) {
		fprintf(stderr, "%s: fseek: %s\n", name, strerror(errno));
		exit(1);
	}
	if (!(tmp = (char *) malloc(len))) {
		fprintf(stderr, "%s: Can't allocate %d bytes.\n", name, len);
		exit(1);
	}
	count = read(file, tmp, len);
	if (count != len) {
		fprintf(stderr, "%s: read: %s.\n",
		     name, count ? strerror(errno) : "End of file reached");
		exit(1);
	}
	return tmp;
}