tools-for-build/grovel-object.c

   1 /*
   2         Grovel a compiled object file for an integer constant.
   3
   4         Example source file:
   5         #include <inttypes.h>
   6         #include <signal.h>
   7         uint64_t values[]={0x0123456789abcdefLL, FPE_INTDIV, 0xfedcba9876543210LL};
   8         int dummy[]={5, 6, 7, 8};
   9         void test() { char *s = (char *)values; s = (char *)dummy; }
  10 */
  11
  12 #include <stdio.h>
  13 #include <inttypes.h>
  14
  15 // search for a known pattern in the file
  16 int match(char *buf, FILE *f)
  17 {
  18   int count=0;
  19   char c;
  20   while(fread(&c, 1, 1, f))
  21     {
  22       if(c==buf[count])
  23         {
  24           count++;
  25         }
  26       else
  27         {
  28           count=0;
  29         }
  30       if(count==8)
  31         return 1;
  32     }
  33   return 0;
  34 }
  35
  36 int main(int argc, char **argv)
  37 {
  38   if(argc!=3 || !(argv[1][0]=='0' || argv[1][0]=='1'))
  39     {
  40       printf("argc: %d\n", argc);
  41       printf("argv[2]: %s\n", argv[2]);
  42       // 0 = little-endian
  43       // 1 = big-endian
  44       printf("Usage: %s {0,1} <input-file>\n", argv[0]);
  45       return 1;
  46     }
  47
  48   FILE *f=fopen(argv[2], "r");
  49   if(!f)
  50     {
  51       printf("Error: could not open '%s'", argv[1]);
  52       return 2;
  53     }
  54
  55   // constants can be up to 64 bits = 8 bytes long
  56   // format:  0x01234567xxxxxxxx76543210
  57   int count=0;
  58   char buf;
  59   // count up
  60   uint64_t value=0;
  61   if(argv[1][0]=='0')
  62     {
  63       // little endian
  64       unsigned char prefix[]={0xef, 0xcd, 0xab, 0x89, 0x67, 0x45, 0x23, 0x01};
  65       unsigned char suffix[]={0x10, 0x32, 0x54, 0x76, 0x98, 0xba, 0xdc, 0xfe};
  66       if(!match(prefix, f))
  67         return 3;
  68       unsigned char buffer[8];
  69       if(fread(buffer, 8, 1, f)!=1)
  70         return 4;
  71       if(!match(suffix, f))
  72         return 5;
  73
  74       // decode the value
  75       int i;
  76       for(i=0; i<8; i++)
  77         {
  78           value*=8;
  79           value+=buffer[7-i];
  80         }
  81     }
  82   else
  83     {
  84       // big endian
  85       unsigned char prefix[]={0x01, 0x23, 0x45, 0x67, 0x89, 0xab, 0xcd, 0xef};
  86       unsigned char suffix[]={0xfe, 0xdc, 0xba, 0x98, 0x76, 0x54, 0x32, 0x10};
  87       if(!match(prefix, f))
  88         return 6;
  89       unsigned char buffer[8];
  90       if(fread(buffer, 8, 1, f)!=1)
  91         return 7;
  92       if(!match(suffix, f))
  93         return 8;
  94
  95       // decode the value
  96       int i;
  97       for(i=0; i<8; i++)
  98         {
  99           value*=8;
 100           value+=buffer[i];
 101         }
 102     }
 103
 104   if(fclose(f))
 105     return 9;
 106
 107   printf("%llu\n", value);
 108 }