From: oohoseoo AT aol DOT com (OoHOSEoO)
Newsgroups: comp.os.msdos.djgpp
Subject: SIGSEGV from reading an executable...  (?)
Lines: 194
Message-ID: <1998090501154700.VAA20831@ladder01.news.aol.com>
NNTP-Posting-Host: ladder01.news.aol.com
Date: 5 Sep 1998 01:15:47 GMT
Organization: AOL http://www.aol.com
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Precedence: bulk

I wrote a small program that reads each byte from a command line specified file
and displays the byte in binary.  it works perfectly for ascii based files, but
when I try and read executable files I get this error message while processing
the bytes:

Exiting due to signal SIGSEGV
Stack Fault at eip=00001700
eax=00001c78 ebx=009c4040 ecx=009b7f15 edx=009b7f74 esi=00000054 edi=0000d4c0
ebp=46464646 esp=009b7f80 program=C:\MYSTUFF\BINARY.EXE
cs: sel=00f7  base=83260000  limit=009dffff
ds: sel=00ff  base=83260000  limit=009dffff
es: sel=00ff  base=83260000  limit=009dffff
fs: sel=00cf  base=00022570  limit=0000ffff
gs: sel=010f  base=00000000  limit=ffffffff
ss: sel=00ff  base=83260000  limit=009dffff

Call frame traceback EIPs:
  0x00001700


here is the code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

long		getsize(const char*);
int		readfile(const char*, long);
void 		convert(int, char*, char*);
int 		output(long, const char*);

int main(int argc, char* argv[])
{
	long size = 0;

	if(argc == 2){
		if((size = getsize(argv[1])) == 0){
			puts("The file was zero bytes long.\n");
			return 1;
		}
		if(readfile(argv[1], size)){
			return 1;
		}
	}

	return 0;
}


int readfile(const char* argv, long size)
{
	unsigned char buf[32768];
	long amount = 32768;
	long left   = size;
	long read   = 0;
	FILE* fp;

	if((fp = fopen(argv, "rb")) == NULL){
		puts("There was an error opening the file");
		return 1;
	}

	while(left){
		if(left < amount){
			amount = left;
		}
		if((read = fread(buf, 1, amount, fp)) == 0){
			puts("There was an error reading the file");
			return 1;
		}
		output(read, buf);
		left -= amount;
	}

	fclose(fp);
	return 0;
}

int output(long size, const char* buf)
{
	char HI[5];
	char LO[5];
	long count;

	for(count = 0; count < size; count++){
		convert(buf[count], HI, LO);
		printf("%s%s ", HI, LO);	
	}	
	return 0;
}


long getsize(const char* argv)
{
	FILE* fp;
	long curpos = 0;
	long length = 0;
	
	if((fp = fopen(argv, "rb")) == NULL){
		return 0;
	}
	curpos = ftell(fp);

	fseek(fp, 0, SEEK_END);
	length = ftell(fp);

	fseek(fp, curpos, SEEK_SET);
	fclose(fp);

	return length;
}


void convert(int Byte, char* HI, char* LO)
{
	char chr[3];
	int status = 0;

	sprintf(chr, "%X", Byte);
	while(status < 2){
		switch(chr[status]){
			case '1':
				if(!status) strcpy(HI, "0001");
				if(status) strcpy(LO, "0001");
				break;
			case '2':
				if(!status) strcpy(HI, "0010");
				if(status) strcpy(LO, "0010");
				break;
			case '3':
				if(!status) strcpy(HI, "0011");
				if(status) strcpy(LO, "0011");
				break;
			case '4':
				if(!status) strcpy(HI, "0100");
				if(status) strcpy(LO, "0100");
				break;
			case '5':
				if(!status) strcpy(HI, "0101");
				if(status) strcpy(LO, "0101");
				break;
			case '6':
				if(!status) strcpy(HI, "0110");
				if(status) strcpy(LO, "0110");
				break;
			case '7':
				if(!status) strcpy(HI, "0111");
				if(status) strcpy(LO, "0111");
				break;
			case '8':
				if(!status) strcpy(HI, "1000");
				if(status) strcpy(LO, "1000");
				break;
			case '9':
				if(!status) strcpy(HI, "1001");
				if(status) strcpy(LO, "1001");
				break;
			case 'A':
				if(!status) strcpy(HI, "1010");
				if(status) strcpy(LO, "1010");
				break;
			case 'B':
				if(!status) strcpy(HI, "1011");
				if(status) strcpy(LO, "1011");
				break;
			case 'C':
				if(!status) strcpy(HI, "1100");
				if(status) strcpy(LO, "1100");
				break;
			case 'D':
				if(!status) strcpy(HI, "1101");
				if(status) strcpy(LO, "1101");
				break;
			case 'E':
				if(!status) strcpy(HI, "1110");
				if(status) strcpy(LO, "1110");
				break;
			case 'F':
				if(!status) strcpy(HI, "1111");
				if(status) strcpy(LO, "1111");
				break;
		}
		status++;
	}
	return;
}


I'd really appreciate any help you can give, thanks.


James B.  (OoHOSEoO AT aol DOT com)

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