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

char* get_elf_type(Elf32_Ehdr *elf);
void banner(void);
int elf_is_valid(Elf32_Ehdr *elf_hdr);
void die(int line,char *err,int code);
int section_header(Elf32_Shdr *shdr,char *strtable,char *section);

int main(int argc, char *argv[])
{
	int fd = -1;
	char *buf = NULL;
	char *table = NULL;
	char * tochange;
	struct stat elf_stat;
	Elf32_Ehdr *elf_header = NULL;
	Elf32_Shdr *section_hdr = NULL;
	int i,size;
	int off;
	unsigned int vm_addr;
        
	if (argc < 5)
		die(__LINE__,"Usage: ./virtchange <file> <virtual address> <section> <value> [<size>]",-1);
		
	banner();

	vm_addr = atoi(argv[2]);
	
	printf( "@ File name           \t: %s .\n", argv[1] );
	
	if ((fd = open(argv[1],O_RDWR)) <0) /* Open file in read/write mode */
		die(__LINE__,"error opening file",-1);
	
	if( fstat( fd, &elf_stat ) < 0 )  /* Getting size with fstat */
		die(__LINE__,"error getting file size",-1);

	size = elf_stat.st_size;
        
	printf( "@ File size           \t: %d bytes .\n", size );
        
	buf = (char*)malloc(sizeof(char)*size+1);

	if (read(fd,buf,size) != size) /* Read whole file */
		die(__LINE__,"error reading bytes",-1);

	if (!argv[5])
		size = strlen(argv[4]);
	else
		size = atoi(argv[5]);

	tochange = (char*)malloc(size+1);

	memcpy(tochange,argv[4],size);
		
	elf_header = (Elf32_Ehdr *)buf; /* Copy the buffer into elf structure */

	if (elf_is_valid(elf_header) == -1)
		die(__LINE__,"bad elf file",-1);

	printf("@ Type                 \t: %s .\n",get_elf_type(elf_header));

	printf("@ Given address        \t: 0x%x .\n",vm_addr);
    
	printf("\n");

	section_hdr = (Elf32_Shdr *)(buf + elf_header->e_shoff); /* Get first section */
     
	table = (char *)(buf + section_hdr[elf_header->e_shstrndx].sh_offset); /* Table of section name */

	for(i = 0; i < elf_header->e_shnum; i++)
		if (section_header(&section_hdr[i], table,argv[3]))
		{
			off = vm_addr - section_hdr[i].sh_addr;
			pwrite(fd,tochange,size,section_hdr[i].sh_offset + off);
		}

	close(fd);

	free(buf);
	return 0;
}

void die(int line,char *err,int code)
{
	printf("[-]Line %d: %s.\n",line,err);
	exit(code);
}

int elf_is_valid(Elf32_Ehdr *elf_hdr)
{
    if( (elf_hdr->e_ident[EI_MAG0] != 0x7F) ||
        (elf_hdr->e_ident[EI_MAG1] != 'E') ||
        (elf_hdr->e_ident[EI_MAG2] != 'L') ||
        (elf_hdr->e_ident[EI_MAG3] != 'F') )
         return 0;

    if(elf_hdr->e_ident[EI_CLASS] != ELFCLASS32)
        return 0;

    if(elf_hdr->e_ident[EI_DATA] != ELFDATA2LSB)
        return 0;

    return 1;
}

void banner(void)
{
	printf("\t~~~ .section changer ~~~\n\n");
}

char* get_elf_type(Elf32_Ehdr *elf)
{
	char *types[] = { "None" , 
			"Relocatable" , 
			"Executable" , 
			"Shared Object" , 
			"Core" , 
			"Defined Types" };
	
	if (elf_is_valid(elf))
		return (char*)types[elf->e_type];
		
	return NULL;
}

int section_header(Elf32_Shdr *shdr, char *strtable,char * section)
{
	if(!shdr)
		return 0;
        
	if (!strcmp(strtable+shdr->sh_name,section))
	{
		printf("+ Section %s\n", strtable + shdr->sh_name);
		printf("\t@ Address: 0x%x\n", shdr->sh_addr);
		printf("\t@ Offset: 0x%x\n", shdr->sh_offset);
		printf("\t@ Size: %d\n", shdr->sh_size);
		printf("\t@ Address alignment: %d\n", shdr->sh_addralign);
		return 1;
	}
	
	return 0;
}