coffnlist() -- General Function (libc)

Symbol table lookup, COFF format
#include <coff.h>
coffnlist(fn, nlp, names, count)
char *fn;
SYMENT *nlp;
char *names;
int count;

The function coffnlist()  finds one or more names in  the symbol table of a
file in the COFF format.

You must arrange  the names you seek into the  form of a COFF symbol table.
All long  names (i.e.,  names longer than  four characters) must  be strung
together like the COFF  long-symbol-name section.  Give each name an n_type
of -1.  After the call, any unfound names will still have this n_type, as a
sign  that it could  not be  found.  Thus,  you can use  the same  table to
search several different COFF files.

fn points to  the name of the file to  be searched.  nlp points to an array
of type SYMENT. This structure is defined in header file coff.h as follows:

typedef struct  syment  {
    union   {
        char _n_name[SYMNMLEN]; /* Name */
        struct {
            long _n_zeroes; /* If name[0-3] zero, */
            long _n_offset; /* string table offset */
        } _n_n;
        char *_n_nptr[2];
    } _n;
    long        n_value;    /* Value */
    short       n_scnum;    /* Section number */
    unsigned short n_type;  /* Type */
    char        n_sclass;   /* Storage class */
    char        n_numaux;   /* Auxilliary entries */
#pragma align 2
} SYMENT;
#pragma align

count gives the  number of symbols being sought.  If  there are long names,
the displacement works from the names parameter.

Each item being  sought must have 0xFFFF in its  n_type field.  This allows
coffnlist() to be used on several files in order.

coffnlist() opens  and reads the file  pointed to by fn.  It then scans the
symbol table  and tries to  find a symbol  with an n_type  of 0xFFFF.  Upon
finding this entry, coffnlist() fills in the fields of the symbol entry.

coffnlist() returns  zero if anything  goes wrong, such as  an inability to
open the file fn. Otherwise, it returns one.

Example

The following  example looks up three  symbol names in the  symbol table of
file tx.o.

#include <stdio.h>
#include <coff.h>

main()
 {
    int i;
    static SYMENT sym[3];   /* the table of names to find */

    /* the long names section */
    static char long_names[] = "a_very_long_name";
    strcpy(sym[0].n_name, "x"); /* look up x */
    sym[0].n_type = -1;

    strcpy(sym[1].n_name, "y"); /* look up y */
    sym[1].n_type = -1;

    sym[2].n_zeroes = 0;    /* look up a_very_long_name */
    /* the long name table starts with a long giving its length
      * offsets are from the beginning of that long. Therefore
     * the n_offset of the first field is 4 not zero */
    sym[2].n_offset = sizeof(long);
    sym[2].n_type = -1;

    /* do lookups */
    if (!coffnlist("tx.o", sym, long_names, 3))
        exit(1);

    /* show off results */
    for (i = 0; i < 3; i++) {
        if (sym[i].n_type != -1)
            printf("%s found at %x\n",
                (sym[i].n_zeroes ? sym[i].n_name :
                    long_names + sym[i].n_offset - sizeof(long)),
                    sym[i].n_value);
    }
}

See Also

coff.h,
libc,
nlist()

© 2012 by Stephen A. Ness