The AOUT format

The AOUT file format is an executable format which came from UNIX. It's a very simple format, a header of 32 bytes followed by the code and data segment and optional symbol informations.

The header:

typedef struct
{
  short magic;                   /* short is assumed that it is a 16 bit int */
  short vstamp;
  unsigned long tsize;           /* long is assumed that it is a 32 bit int */
  unsigned long dsize;
  unsigned long bsize;
  unsigned long symsize;
  unsigned long entry;
  unsigned long text_start;
  unsigned long data_start;
} aouthdr;

magic is a magic number depending on the system, vstamp can be ignored. tsize is the size of the code segment (t means text segment), dsize the size of the data segment and bsize the size of the BSS (uninitializied data). symsize, text_start and data_start are only important for debugger informations. entry is the entry point to the program.

Remarks:

• The load addresses for the code, data and bss address are implicit, so the loader must know to which address the symbols relocated by the linker
• The most linkers which produce the AOUT-format insert informations about the global symbols into the AOUT format, to avoid this run the utility STRIP after linking (this reduces the size of the AOUT-file)
• For more informations look at the sources of WOS