There are three directives that begin .stab. All emit symbols (refer to Chapter 6 Symbols), for use by symbolic debuggers. The symbols are not entered in the as hash table: they cannot be referenced elsewhere in the source file. Up to five fields are required:
This is the symbol's name. It may contain any character except \000, so is more general than ordinary symbol names. Some debuggers used to code arbitrarily complex structures into symbol names using this field.
An absolute expression. The symbol's type is set to the low 8 bits of this expression. Any bit pattern is permitted, but ld and debuggers choke on silly bit patterns.
An absolute expression. The symbol's "other" attribute is set to the low 8 bits of this expression.
An absolute expression. The symbol's descriptor is set to the low 16 bits of this expression.
An absolute expression which becomes the symbol's value.
If a warning is detected while reading a .stabd, .stabn, or .stabs statement, the symbol has probably already been created; you get a half-formed symbol in your object file. This is compatible with earlier assemblers!
The "name" of the symbol generated is not even an empty string. It is a null pointer, for compatibility. Older assemblers used a null pointer so they didn't waste space in object files with empty strings.
The symbol's value is set to the location counter, relocatably. When your program is linked, the value of this symbol is the address of the location counter when the .stabd was assembled.
The name of the symbol is set to the empty string "".
All five fields are specified.