rmflags.c

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/* rmphdr.c
/*      read the elf format object file, and remove
/*      program execution headers and nullify allocation flags,
/*      so that the file is used to provide only relocation
/*      information for a EusLisp's compiled code.
/*
/* May/1994     (c) Toshihiro Matsui, Electrotechnical Laboratory
/*
*/


#include <stdio.h>
#include <sys/types.h>
#include <libelf.h>     /* sys/elf.h is read */
#include <fcntl.h>

#define min(x,y) ((x)<(y)?(x):(y))

extern int errno;


void copy_bytes(infd, outfd, offset, nbytes)
int infd, outfd, offset, nbytes;
{ char buf[8192];
  int  i, s;
  lseek(infd, offset, SEEK_SET);
  while (nbytes>0) {
    s=min(8192, nbytes);
    s=read(infd, buf, s);
    if (s<=0) { 
        fprintf(stderr, "cannot read object %d", errno);
        return;}
    write(outfd, buf, s);
    nbytes -= s;}
  }


main(argc,argv)
int argc;
char *argv[];
{
  char *fname;
  int elfd, outfd;
  char outfname[128];
  Elf *elf;
  Elf32_Ehdr *ehdr, newehdr;
  Elf_Scn *scn;
  Elf32_Shdr *scnhdr, scntab[40];
  Elf_Data *data;
  int scn_symt[40];
  int i, j, scn_num, scn_total_size, scn_offset;
  char *cp;
  

  fname=argv[1];
  sprintf(outfname,"%s.p",fname);
  elfd=open(fname, 0);
  outfd=open(outfname, O_RDWR | O_CREAT, 0777);
  if (elfd<=0) {
    fprintf(stderr, "%s cannot open %d\n", fname, errno);
    exit(2);}
  if (outfd<=0) {
    fprintf(stderr, "%s cannot open %d\n", outfname, errno);
    exit(2);}
  fprintf(stderr, "%s opened\n", outfname);

  elf_version(EV_CURRENT);
  elf=elf_begin(elfd, ELF_C_READ, 0);
  if (elf==0) printf("%s\n", elf_errmsg(elf_errno()));
  ehdr=elf32_getehdr(elf);
  memcpy(&newehdr, ehdr, sizeof(newehdr));
/*  printf("elfhdr=%x\n", ehdr); */
/*  printf("e_ident="); */
/*  for (i=0; i<16; i++) {  printf("%2x ", ehdr->e_ident[i]);} */

  printf("\ne_type= %d\n", newehdr.e_type);
  printf("e_machine= %d\n", newehdr.e_machine);
  printf("e_version= %d\n", newehdr.e_version);
  printf("e_entry= 0x%x\n", newehdr.e_entry);
  printf("e_phoff= 0x%x\n", newehdr.e_phoff);
  printf("e_shoff= 0x%x\n", newehdr.e_shoff);
  printf("e_flags= 0x%x\n", newehdr.e_flags);
  printf("e_ehsize= 0x%x\n", newehdr.e_ehsize);
  printf("e_phentsize= %d\n", newehdr.e_phentsize);
  printf("e_phnum= %d\n", newehdr.e_phnum);
  printf("e_shentsize= %d\n", newehdr.e_shentsize);
  printf("e_shnum= %d\n", newehdr.e_shnum);
  printf("e_shstrndx= %d\n", newehdr.e_shstrndx);

  /* get all section headers, and remove flags */
  scn_num=newehdr.e_shnum;
  scn_total_size=0;
  for (i=0; i<scn_num; i++) {
    scn=elf_getscn(elf, i);
    scnhdr=elf32_getshdr(scn);
    memcpy(&scntab[i], scnhdr, sizeof(Elf32_Shdr));
    if (scntab[i].sh_flags) {
      scntab[i].sh_flags=0;     /* no write, alloc, or inst bit */
      if (scntab[i].sh_type==SHT_PROGBITS)
        scntab[i].sh_size=0;}
    scn_total_size +=scntab[i].sh_size; } 

  /* prepare a new elf header */
  newehdr.e_type=ET_REL;        /*relocatable*/
  newehdr.e_entry=0;
  newehdr.e_phoff=0;    /* no program execution header*/
  newehdr.e_shoff= sizeof(Elf32_Ehdr) + scn_total_size;
  newehdr.e_phentsize=0;
  newehdr.e_phnum=0;

  /* write new elf header */
  write(outfd, &newehdr, sizeof(Elf32_Ehdr));
  fprintf(stderr, "ehdr updated\n");

  /* ignore phdr's written */
  /* copy section contents */
  for (i=1; i<scn_num; i++) {
    fprintf(stderr, "%d size=%d\n", i, scntab[i].sh_size);
    copy_bytes(elfd, outfd, scntab[i].sh_offset, scntab[i].sh_size);
    }

  /* write updated section headers */
  /* write zeroth header */
  scn_offset=sizeof(Elf32_Ehdr);
  write(outfd, scntab[0], sizeof(Elf32_Shdr));

  /* write section headers */
  for (i=1; i<scn_num; i++) {
    scntab[i].sh_offset=scn_offset;
    scn_offset += scntab[i].sh_size;
    write(outfd, scntab[i], sizeof(Elf32_Shdr));
    }

  elf_end(elf);
  close(elfd);
  close(outfd);
  }