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* stabs.texinfo (Local Variable Parameters): Talk about nameless

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parameters on VAX.
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Jim Kingdon 1993-09-07 00:26:57 +00:00
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5
gdb/doc/ChangeLog
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@ -1,3 +1,8 @@
Mon Sep 6 19:23:18 1993 Jim Kingdon (kingdon@lioth.cygnus.com)
* stabs.texinfo (Local Variable Parameters): Talk about nameless
parameters on VAX.
Fri Sep 3 17:06:08 1993 Roland H. Pesch (pesch@fowanton.cygnus.com)
* gdb.texinfo: @up/@down -> @raisesections/@lowersections

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gdb/doc/stabs.texinfo
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@ -1033,13 +1033,38 @@ Some compilers use the pair of symbols approach described above
(sometimes) when the argument type is @code{float} and it is passed as a
@code{double} and converted to @code{float} by the prologue (in the
latter case the type of the @samp{@var{arg}:p} symbol is @code{double}
and the type of the @samp{@var{arg}:} symbol is @code{float}). GCC, at
least on the 960, uses a single @samp{p} symbol descriptor for an
argument which is stored as a local variable but uses @code{N_LSYM}
instead of @code{N_PSYM}. In this case, the value of the symbol
is an offset relative to the local variables for that function, not
relative to the arguments; on some machines those are the same thing,
but not on all.
and the type of the @samp{@var{arg}:} symbol is @code{float}).
GCC, at least on the 960, has another solution to the same problem. It
uses a single @samp{p} symbol descriptor for an argument which is stored
as a local variable but uses @code{N_LSYM} instead of @code{N_PSYM}. In
this case, the value of the symbol is an offset relative to the local
variables for that function, not relative to the arguments; on some
machines those are the same thing, but not on all.
@c This is mostly just background info; the part that logically belongs
@c here is the last sentence.
On the VAX or on other machines in which the calling convention includes
the number of words of arguments actually passed, the debugger (GDB at
least) uses the parameter symbols to keep track of whether it needs to
print nameless arguments in addition to the formal parameters which it
has printed because each one has a stab. For example, in
@example
extern int fprintf (FILE *stream, char *format, @dots{});
@dots{}
fprintf (stdout, "%d\n", x);
@end example
there are stabs for @code{stream} and @code{format}. On most machines,
the debugger can only print those two arguments (because it has no way
of knowing that additional arguments were passed), but on the VAX or
other machines with a calling convention which indicates the number of
words of arguments, the debugger can print all three arguments. To do
so, the parameter symbol (symbol descriptor @samp{p}) (not necessarily
@samp{r} or symbol descriptor omitted symbols) needs to contain the
actual type as passed (for example, @code{double} not @code{float} if it
is passed as a double and converted to a float).
@node Reference Parameters
@subsection Passing Parameters by Reference