Line numbers

When invoked with cc -g the compiler causes an entry in the object file for every source line where a breakpoint can be inserted. You can then reference line numbers when using a software debugger like sdb(CP). All line numbers in a section are grouped by function as shown in ``Line number grouping''.

Line number grouping

symbol index	0
physical address	line number
physical address	line number
.	.
.	.
.	.
symbol index	0
physical address	line number
physical address	line number

The first entry in a function grouping has line number 0 and has, in place of the physical address, an index into the symbol table for the entry containing the function name. Subsequent entries have actual line numbers and addresses of the text corresponding to the line numbers. The line number entries are relative to the beginning of the function and appear in increasing order of address.

Line number declaration

The structure declaration currently used for line number entries is shown below.

   struct lineno
   {
       union
       {
                 long  l_symndx;  /* symtbl index of func name */
                 long  l_paddr;   /* paddr of line number */
       } l_addr;
       unsigned short  l_lnno;    /* line number */
   };
   

   #define LINENO      struct lineno
   #define LINESZ      6