objtype, readobj, objtraverse, isar, nextar, readar – object file interpretation functions


#include <u.h>
#include <libc.h>
#include <bio.h>
#include <mach.h>

int objtype(Biobuf *bp, char **name)

int readobj(Biobuf *bp, int objtype)

void objtraverse(void(*)(Sym*, void*), void*)

int isar(Biobuf *bp)

int nextar(Biobuf *bp, int offset, char *buf)

int readar(Biobuf *bp, int objtype, vlong end, int doautos)


These functions provide machine-independent access to object files in a directory or an archive. Mach(2) and symbol(2) describe additional library functions for interpreting executable files and executing images.

Object files contain no formal symbol table; instead, references to symbols must be extracted from the encoded object representation and resolved. The resulting symbol information is loaded into a dummy symbol table where it is available for processing by an application. The organization of the dummy symbol table is identical to that produced by the loader and described in symbol(2) and a.out(6): a vector of Sym data structures defining the name, type and relative offset of each symbol.

Objtype reads the header at the current position of the file associated with bp (see Bio(2)) to see if it is an intermediate object file. If it is, a code indicating the architecture type of the file is returned and the second argument, if it is non-zero, is set pointing to a string describing the type of the file. If the header does not indicate an object file, –1 is returned. The header may be at the start of an object file or at the beginning of an archive member. The file is rewound to its starting position after decoding the header.

Readobj constructs a symbol table for the object file associated with bp. The second argument contains the type code produced by function objtype. The file must be positioned at the start of the object file. Each invocation of readobj destroys the symbol definitions for any previous file.

Objtraverse scans the symbol table previously built by readobj or readar. Objtraverse requires two arguments: the address of a call-back function and a generic pointer. The call-back function is invoked once for each symbol in the symbol table with the address of a Sym data structure as the first argument and the generic pointer as the second.

Isar reads the header at the current point in the file associated with bp and returns 1 if it is an archive or zero otherwise. The file is positioned at the end of the archive header and at the beginning of the first member of the archive.

Nextar extracts information describing the archive member stored at offset in the file associated with bp. If the header describing the member can be extracted and decoded, the size of the member is returned. Adding this value to offset yields the offset of the beginning of the next member in the archive. On return the input file is positioned at the end of the member header and the name of the member is stored in buf, a buffer of SARNAME characters. If there are no more members, nextar returns zero; a negative return indicates a missing or malformed header.

Readar constructs the symbol table of the object file stored at the current position in the archive associated with bp. This function operates exactly as readobj; the only difference is the extra argument, end, specifying the offset to the beginning of the next member in the archive. Readar leaves the file positioned at that point.




mach(2), symbol(2), bio(2), a.out(6)


These routines set errstr.