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* gdbint.texinfo (COERCE_FLOAT_TO_DOUBLE): Clarify.

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Jim Blandy 2001-11-13 18:52:53 +00:00
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gdb/doc/ChangeLog
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@ -1,3 +1,7 @@
2001-11-13 Jim Blandy <jimb@redhat.com>
* gdbint.texinfo (COERCE_FLOAT_TO_DOUBLE): Clarify.
2001-11-06 Corinna Vinschen <vinschen@redhat.com>
* gdb.texinfo (gdbarch_in_function_epilogue_p): Add documentation.

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gdb/doc/gdbint.texinfo
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@ -2815,30 +2815,46 @@ Currently only implemented correctly for native Sparc configurations?
@item COERCE_FLOAT_TO_DOUBLE (@var{formal}, @var{actual})
@findex COERCE_FLOAT_TO_DOUBLE
@cindex promotion to @code{double}
If we are calling a function by hand, and the function was declared
(according to the debug info) without a prototype, should we
automatically promote @code{float}s to @code{double}s? This macro
must evaluate to non-zero if we should, or zero if we should leave the
value alone.
@cindex @code{float} arguments
@cindex prototyped functions, passing arguments to
@cindex passing arguments to prototyped functions
Return non-zero if GDB should promote @code{float} values to
@code{double} when calling a non-prototyped function. The argument
@var{actual} is the type of the value we want to pass to the function.
The argument @var{formal} is the type of this argument, as it appears in
the function's definition. Note that @var{formal} may be zero if we
have no debugging information for the function, or if we're passing more
arguments than are officially declared (for example, varargs). This
macro is never invoked if the function definitely has a prototype.
The argument @var{actual} is the type of the value we want to pass to
the function. The argument @var{formal} is the type of this argument,
as it appears in the function's definition. Note that @var{formal} may
be zero if we have no debugging information for the function, or if
we're passing more arguments than are officially declared (for example,
varargs). This macro is never invoked if the function definitely has a
prototype.
How you should pass arguments to a function depends on whether it was
defined in K&R style or prototype style. If you define a function using
the K&R syntax that takes a @code{float} argument, then callers must
pass that argument as a @code{double}. If you define the function using
the prototype syntax, then you must pass the argument as a @code{float},
with no promotion.
Unfortunately, on certain older platforms, the debug info doesn't
indicate reliably how each function was defined. A function type's
@code{TYPE_FLAG_PROTOTYPED} flag may be unset, even if the function was
defined in prototype style. When calling a function whose
@code{TYPE_FLAG_PROTOTYPED} flag is unset, GDB consults the
@code{COERCE_FLOAT_TO_DOUBLE} macro to decide what to do.
@findex set_gdbarch_coerce_float_to_double
@findex standard_coerce_float_to_double
The default behavior is to promote only when we have no type information
for the formal parameter. This is different from the obvious behavior,
which would be to promote whenever we have no prototype, just as the
compiler does. It's annoying, but some older targets rely on this. If
you want @value{GDBN} to follow the typical compiler behavior---to always
promote when there is no prototype in scope---your gdbarch @code{init}
function can call @code{set_gdbarch_coerce_float_to_double} and select
the @code{standard_coerce_float_to_double} function.
For modern targets, it is proper to assume that, if the prototype flag
is unset, that can be trusted: @code{float} arguments should be promoted
to @code{double}. You should use the function
@code{standard_coerce_float_to_double} to get this behavior.
@findex default_coerce_float_to_double
For some older targets, if the prototype flag is unset, that doesn't
tell us anything. So we guess that, if we don't have a type for the
formal parameter (@i{i.e.}, the first argument to
@code{COERCE_FLOAT_TO_DOUBLE} is null), then we should promote it;
otherwise, we should leave it alone. The function
@code{default_coerce_float_to_double} provides this behavior; it is the
default value, for compatibility with older configurations.
@item CPLUS_MARKER
@findex CPLUS_MARKERz