Lxx vs .Lxxx - gcc vs gas

Ronald F. Guilmette rfg@segfault.us.com
Sat Jun 17 17:00:00 GMT 1995


In message < 199506172158.RAA25682@delorie.com >, you wrote:

>
>[Be careful when replying; this was sent to two mailing lists - DJ]
>
>There are two types of "local" labels used by gcc and gas:
>
>(1)	Lfoo:
>(2)	.Lfoo:
>
>gcc chooses which to use based on whether the target prepends an
>underscore to external symbols or not.

I'm not sure if that is a proper way to make the distinction, but it
might be.  Then again, it might not.

What I _can_ tell you is that the convention on ELF-based systems is
_not_ to put an underscore before a user-declared identifier (when
converting it from the C level to the assembly level).  This differs
from the older UNIX tradition of putting one underscore in front of
each user-declared name (at the assembly level).

I believe that for most COFF-based systems, the convention was to prepend
a leading underscore to the names of all entities which were declared by
the user at the C-language level.  (But I might be wrong about that.  It
has been a LONG time since I used COFF.)

Separately, there is the question of what prefix will force the assembler
NOT to write a given label into the symbol table of the object file.  In
the case of all ELF assemblers that I am familiar with, a leading period
will cause the relevant label NOT to appear in the symbol table of the
resulting object file... but these conventions are highly assembler-
dependent, and I don't knon that there is any hard-and-fast rule by
which you could predict (for any given assembler) what the ``hiding
prefix'' is.  You just have to try some experiments and see.

>gas chooses which to use based on whether the output object format is
>COFF or not (for the i386, at least).

I think that's probably wrong.  If you had said that GAS uses leading
periods as the ``hiding prefix'' for _both_ COFF and ELF, then I might
believe that gas was doing the Right Thing.  Even then however, I think
that the wisest thing to do (in _both_ gas and gcc) would be to establish
an entirely separate and independent target macro to control/determine
the ``hiding prefix''.

>DJGPP is coff with underscores, and the two don't agree on which is
>right, so I end up with all the local labels in the object's symbol
>table.
>
>Which should I fix?  Is there a global solution, or will I need a
>special case for djgpp?

See above.  I think that _somebody_ should fix both gas and gcc so that
the assembly-level ``hiding prefix'' can be specified independently from
everything else.  I really don't think that there is 100% correlation
between the object file format and the hiding prefix.  Any correlations
which seem to relate one to the other are, I believe, simply the product
of luck rather than the product of universal rules or universally obeyed
conventions.


-- Ron Guilmette, Sunnyvale, CA -------- RG Consulting ---------------------
---- E-mail: rfg@segfault.us.com --------Purveyors of Compiler Test Suites -
---- finger: rfg@rahul.net -------------------------------------------------




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