(stabs) Line Numbers

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 Line Numbers
 ============
 
    An `N_SLINE' symbol represents the start of a source line.  The desc
 field contains the line number and the value contains the code address
 for the start of that source line.  On most machines the address is
 absolute; for stabs in sections ( Stab Sections), it is relative
 to the function in which the `N_SLINE' symbol occurs.
 
    GNU documents `N_DSLINE' and `N_BSLINE' symbols for line numbers in
 the data or bss segments, respectively.  They are identical to
 `N_SLINE' but are relocated differently by the linker.  They were
 intended to be used to describe the source location of a variable
 declaration, but I believe that GCC2 actually puts the line number in
 the desc field of the stab for the variable itself.  GDB has been
 ignoring these symbols (unless they contain a string field) since at
 least GDB 3.5.
 
    For single source lines that generate discontiguous code, such as
 flow of control statements, there may be more than one line number
 entry for the same source line.  In this case there is a line number
 entry at the start of each code range, each with the same line number.
 
    XCOFF does not use stabs for line numbers.  Instead, it uses COFF
 line numbers (which are outside the scope of this document).  Standard
 COFF line numbers cannot deal with include files, but in XCOFF this is
 fixed with the `C_BINCL' method of marking include files ( Include
 Files).
 

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