You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
299 lines
16 KiB
HTML
299 lines
16 KiB
HTML
4 years ago
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
|
||
|
|
<html>
|
||
|
|
<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
|
||
|
|
|
||
|
|
Permission is granted to copy, distribute and/or modify this document
|
||
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
||
|
|
any later version published by the Free Software Foundation; with the
|
||
|
|
Invariant Sections being "Funding Free Software", the Front-Cover
|
||
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
||
|
|
(see below). A copy of the license is included in the section entitled
|
||
|
|
"GNU Free Documentation License".
|
||
|
|
|
||
|
|
(a) The FSF's Front-Cover Text is:
|
||
|
|
|
||
|
|
A GNU Manual
|
||
|
|
|
||
|
|
(b) The FSF's Back-Cover Text is:
|
||
|
|
|
||
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
||
|
|
software. Copies published by the Free Software Foundation raise
|
||
|
|
funds for GNU development. -->
|
||
|
|
<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<title>Varargs (GNU Compiler Collection (GCC) Internals)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Varargs (GNU Compiler Collection (GCC) Internals)">
|
||
|
|
<meta name="keywords" content="Varargs (GNU Compiler Collection (GCC) Internals)">
|
||
|
|
<meta name="resource-type" content="document">
|
||
|
|
<meta name="distribution" content="global">
|
||
|
|
<meta name="Generator" content="makeinfo">
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
||
|
|
<link href="index.html#Top" rel="start" title="Top">
|
||
|
|
<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="Target-Macros.html#Target-Macros" rel="up" title="Target Macros">
|
||
|
|
<link href="Trampolines.html#Trampolines" rel="next" title="Trampolines">
|
||
|
|
<link href="Miscellaneous-Register-Hooks.html#Miscellaneous-Register-Hooks" rel="prev" title="Miscellaneous Register Hooks">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.summary-letter {text-decoration: none}
|
||
|
|
blockquote.indentedblock {margin-right: 0em}
|
||
|
|
blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
|
||
|
|
blockquote.smallquotation {font-size: smaller}
|
||
|
|
div.display {margin-left: 3.2em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
div.lisp {margin-left: 3.2em}
|
||
|
|
div.smalldisplay {margin-left: 3.2em}
|
||
|
|
div.smallexample {margin-left: 3.2em}
|
||
|
|
div.smalllisp {margin-left: 3.2em}
|
||
|
|
kbd {font-style: oblique}
|
||
|
|
pre.display {font-family: inherit}
|
||
|
|
pre.format {font-family: inherit}
|
||
|
|
pre.menu-comment {font-family: serif}
|
||
|
|
pre.menu-preformatted {font-family: serif}
|
||
|
|
pre.smalldisplay {font-family: inherit; font-size: smaller}
|
||
|
|
pre.smallexample {font-size: smaller}
|
||
|
|
pre.smallformat {font-family: inherit; font-size: smaller}
|
||
|
|
pre.smalllisp {font-size: smaller}
|
||
|
|
span.nolinebreak {white-space: nowrap}
|
||
|
|
span.roman {font-family: initial; font-weight: normal}
|
||
|
|
span.sansserif {font-family: sans-serif; font-weight: normal}
|
||
|
|
ul.no-bullet {list-style: none}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<a name="Varargs"></a>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Trampolines.html#Trampolines" accesskey="n" rel="next">Trampolines</a>, Previous: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="p" rel="prev">Stack and Calling</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<a name="Implementing-the-Varargs-Macros"></a>
|
||
|
|
<h3 class="section">18.10 Implementing the Varargs Macros</h3>
|
||
|
|
<a name="index-varargs-implementation"></a>
|
||
|
|
|
||
|
|
<p>GCC comes with an implementation of <code><varargs.h></code> and
|
||
|
|
<code><stdarg.h></code> that work without change on machines that pass arguments
|
||
|
|
on the stack. Other machines require their own implementations of
|
||
|
|
varargs, and the two machine independent header files must have
|
||
|
|
conditionals to include it.
|
||
|
|
</p>
|
||
|
|
<p>ISO <code><stdarg.h></code> differs from traditional <code><varargs.h></code> mainly in
|
||
|
|
the calling convention for <code>va_start</code>. The traditional
|
||
|
|
implementation takes just one argument, which is the variable in which
|
||
|
|
to store the argument pointer. The ISO implementation of
|
||
|
|
<code>va_start</code> takes an additional second argument. The user is
|
||
|
|
supposed to write the last named argument of the function here.
|
||
|
|
</p>
|
||
|
|
<p>However, <code>va_start</code> should not use this argument. The way to find
|
||
|
|
the end of the named arguments is with the built-in functions described
|
||
|
|
below.
|
||
|
|
</p>
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-_005f_005fbuiltin_005fsaveregs"></a>Macro: <strong>__builtin_saveregs</strong> <em>()</em></dt>
|
||
|
|
<dd><p>Use this built-in function to save the argument registers in memory so
|
||
|
|
that the varargs mechanism can access them. Both ISO and traditional
|
||
|
|
versions of <code>va_start</code> must use <code>__builtin_saveregs</code>, unless
|
||
|
|
you use <code>TARGET_SETUP_INCOMING_VARARGS</code> (see below) instead.
|
||
|
|
</p>
|
||
|
|
<p>On some machines, <code>__builtin_saveregs</code> is open-coded under the
|
||
|
|
control of the target hook <code>TARGET_EXPAND_BUILTIN_SAVEREGS</code>. On
|
||
|
|
other machines, it calls a routine written in assembler language,
|
||
|
|
found in <samp>libgcc2.c</samp>.
|
||
|
|
</p>
|
||
|
|
<p>Code generated for the call to <code>__builtin_saveregs</code> appears at the
|
||
|
|
beginning of the function, as opposed to where the call to
|
||
|
|
<code>__builtin_saveregs</code> is written, regardless of what the code is.
|
||
|
|
This is because the registers must be saved before the function starts
|
||
|
|
to use them for its own purposes.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-_005f_005fbuiltin_005fnext_005farg"></a>Macro: <strong>__builtin_next_arg</strong> <em>(<var>lastarg</var>)</em></dt>
|
||
|
|
<dd><p>This builtin returns the address of the first anonymous stack
|
||
|
|
argument, as type <code>void *</code>. If <code>ARGS_GROW_DOWNWARD</code>, it
|
||
|
|
returns the address of the location above the first anonymous stack
|
||
|
|
argument. Use it in <code>va_start</code> to initialize the pointer for
|
||
|
|
fetching arguments from the stack. Also use it in <code>va_start</code> to
|
||
|
|
verify that the second parameter <var>lastarg</var> is the last named argument
|
||
|
|
of the current function.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-_005f_005fbuiltin_005fclassify_005ftype"></a>Macro: <strong>__builtin_classify_type</strong> <em>(<var>object</var>)</em></dt>
|
||
|
|
<dd><p>Since each machine has its own conventions for which data types are
|
||
|
|
passed in which kind of register, your implementation of <code>va_arg</code>
|
||
|
|
has to embody these conventions. The easiest way to categorize the
|
||
|
|
specified data type is to use <code>__builtin_classify_type</code> together
|
||
|
|
with <code>sizeof</code> and <code>__alignof__</code>.
|
||
|
|
</p>
|
||
|
|
<p><code>__builtin_classify_type</code> ignores the value of <var>object</var>,
|
||
|
|
considering only its data type. It returns an integer describing what
|
||
|
|
kind of type that is—integer, floating, pointer, structure, and so on.
|
||
|
|
</p>
|
||
|
|
<p>The file <samp>typeclass.h</samp> defines an enumeration that you can use to
|
||
|
|
interpret the values of <code>__builtin_classify_type</code>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<p>These machine description macros help implement varargs:
|
||
|
|
</p>
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fEXPAND_005fBUILTIN_005fSAVEREGS"></a>Target Hook: <em>rtx</em> <strong>TARGET_EXPAND_BUILTIN_SAVEREGS</strong> <em>(void)</em></dt>
|
||
|
|
<dd><p>If defined, this hook produces the machine-specific code for a call to
|
||
|
|
<code>__builtin_saveregs</code>. This code will be moved to the very
|
||
|
|
beginning of the function, before any parameter access are made. The
|
||
|
|
return value of this function should be an RTX that contains the value
|
||
|
|
to use as the return of <code>__builtin_saveregs</code>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fSETUP_005fINCOMING_005fVARARGS"></a>Target Hook: <em>void</em> <strong>TARGET_SETUP_INCOMING_VARARGS</strong> <em>(cumulative_args_t <var>args_so_far</var>, machine_mode <var>mode</var>, tree <var>type</var>, int *<var>pretend_args_size</var>, int <var>second_time</var>)</em></dt>
|
||
|
|
<dd><p>This target hook offers an alternative to using
|
||
|
|
<code>__builtin_saveregs</code> and defining the hook
|
||
|
|
<code>TARGET_EXPAND_BUILTIN_SAVEREGS</code>. Use it to store the anonymous
|
||
|
|
register arguments into the stack so that all the arguments appear to
|
||
|
|
have been passed consecutively on the stack. Once this is done, you can
|
||
|
|
use the standard implementation of varargs that works for machines that
|
||
|
|
pass all their arguments on the stack.
|
||
|
|
</p>
|
||
|
|
<p>The argument <var>args_so_far</var> points to the <code>CUMULATIVE_ARGS</code> data
|
||
|
|
structure, containing the values that are obtained after processing the
|
||
|
|
named arguments. The arguments <var>mode</var> and <var>type</var> describe the
|
||
|
|
last named argument—its machine mode and its data type as a tree node.
|
||
|
|
</p>
|
||
|
|
<p>The target hook should do two things: first, push onto the stack all the
|
||
|
|
argument registers <em>not</em> used for the named arguments, and second,
|
||
|
|
store the size of the data thus pushed into the <code>int</code>-valued
|
||
|
|
variable pointed to by <var>pretend_args_size</var>. The value that you
|
||
|
|
store here will serve as additional offset for setting up the stack
|
||
|
|
frame.
|
||
|
|
</p>
|
||
|
|
<p>Because you must generate code to push the anonymous arguments at
|
||
|
|
compile time without knowing their data types,
|
||
|
|
<code>TARGET_SETUP_INCOMING_VARARGS</code> is only useful on machines that
|
||
|
|
have just a single category of argument register and use it uniformly
|
||
|
|
for all data types.
|
||
|
|
</p>
|
||
|
|
<p>If the argument <var>second_time</var> is nonzero, it means that the
|
||
|
|
arguments of the function are being analyzed for the second time. This
|
||
|
|
happens for an inline function, which is not actually compiled until the
|
||
|
|
end of the source file. The hook <code>TARGET_SETUP_INCOMING_VARARGS</code> should
|
||
|
|
not generate any instructions in this case.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fSTRICT_005fARGUMENT_005fNAMING"></a>Target Hook: <em>bool</em> <strong>TARGET_STRICT_ARGUMENT_NAMING</strong> <em>(cumulative_args_t <var>ca</var>)</em></dt>
|
||
|
|
<dd><p>Define this hook to return <code>true</code> if the location where a function
|
||
|
|
argument is passed depends on whether or not it is a named argument.
|
||
|
|
</p>
|
||
|
|
<p>This hook controls how the <var>named</var> argument to <code>TARGET_FUNCTION_ARG</code>
|
||
|
|
is set for varargs and stdarg functions. If this hook returns
|
||
|
|
<code>true</code>, the <var>named</var> argument is always true for named
|
||
|
|
arguments, and false for unnamed arguments. If it returns <code>false</code>,
|
||
|
|
but <code>TARGET_PRETEND_OUTGOING_VARARGS_NAMED</code> returns <code>true</code>,
|
||
|
|
then all arguments are treated as named. Otherwise, all named arguments
|
||
|
|
except the last are treated as named.
|
||
|
|
</p>
|
||
|
|
<p>You need not define this hook if it always returns <code>false</code>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fCALL_005fARGS"></a>Target Hook: <em>void</em> <strong>TARGET_CALL_ARGS</strong> <em>(rtx, <var>tree</var>)</em></dt>
|
||
|
|
<dd><p>While generating RTL for a function call, this target hook is invoked once
|
||
|
|
for each argument passed to the function, either a register returned by
|
||
|
|
<code>TARGET_FUNCTION_ARG</code> or a memory location. It is called just
|
||
|
|
before the point where argument registers are stored. The type of the
|
||
|
|
function to be called is also passed as the second argument; it is
|
||
|
|
<code>NULL_TREE</code> for libcalls. The <code>TARGET_END_CALL_ARGS</code> hook is
|
||
|
|
invoked just after the code to copy the return reg has been emitted.
|
||
|
|
This functionality can be used to perform special setup of call argument
|
||
|
|
registers if a target needs it.
|
||
|
|
For functions without arguments, the hook is called once with <code>pc_rtx</code>
|
||
|
|
passed instead of an argument register.
|
||
|
|
Most ports do not need to implement anything for this hook.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fEND_005fCALL_005fARGS"></a>Target Hook: <em>void</em> <strong>TARGET_END_CALL_ARGS</strong> <em>(void)</em></dt>
|
||
|
|
<dd><p>This target hook is invoked while generating RTL for a function call,
|
||
|
|
just after the point where the return reg is copied into a pseudo. It
|
||
|
|
signals that all the call argument and return registers for the just
|
||
|
|
emitted call are now no longer in use.
|
||
|
|
Most ports do not need to implement anything for this hook.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fPRETEND_005fOUTGOING_005fVARARGS_005fNAMED"></a>Target Hook: <em>bool</em> <strong>TARGET_PRETEND_OUTGOING_VARARGS_NAMED</strong> <em>(cumulative_args_t <var>ca</var>)</em></dt>
|
||
|
|
<dd><p>If you need to conditionally change ABIs so that one works with
|
||
|
|
<code>TARGET_SETUP_INCOMING_VARARGS</code>, but the other works like neither
|
||
|
|
<code>TARGET_SETUP_INCOMING_VARARGS</code> nor <code>TARGET_STRICT_ARGUMENT_NAMING</code> was
|
||
|
|
defined, then define this hook to return <code>true</code> if
|
||
|
|
<code>TARGET_SETUP_INCOMING_VARARGS</code> is used, <code>false</code> otherwise.
|
||
|
|
Otherwise, you should not define this hook.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fLOAD_005fBOUNDS_005fFOR_005fARG"></a>Target Hook: <em>rtx</em> <strong>TARGET_LOAD_BOUNDS_FOR_ARG</strong> <em>(rtx <var>slot</var>, rtx <var>arg</var>, rtx <var>slot_no</var>)</em></dt>
|
||
|
|
<dd><p>This hook is used by expand pass to emit insn to load bounds of
|
||
|
|
<var>arg</var> passed in <var>slot</var>. Expand pass uses this hook in case
|
||
|
|
bounds of <var>arg</var> are not passed in register. If <var>slot</var> is a
|
||
|
|
memory, then bounds are loaded as for regular pointer loaded from
|
||
|
|
memory. If <var>slot</var> is not a memory then <var>slot_no</var> is an integer
|
||
|
|
constant holding number of the target dependent special slot which
|
||
|
|
should be used to obtain bounds. Hook returns RTX holding loaded bounds.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fSTORE_005fBOUNDS_005fFOR_005fARG"></a>Target Hook: <em>void</em> <strong>TARGET_STORE_BOUNDS_FOR_ARG</strong> <em>(rtx <var>arg</var>, rtx <var>slot</var>, rtx <var>bounds</var>, rtx <var>slot_no</var>)</em></dt>
|
||
|
|
<dd><p>This hook is used by expand pass to emit insns to store <var>bounds</var> of
|
||
|
|
<var>arg</var> passed in <var>slot</var>. Expand pass uses this hook in case
|
||
|
|
<var>bounds</var> of <var>arg</var> are not passed in register. If <var>slot</var> is a
|
||
|
|
memory, then <var>bounds</var> are stored as for regular pointer stored in
|
||
|
|
memory. If <var>slot</var> is not a memory then <var>slot_no</var> is an integer
|
||
|
|
constant holding number of the target dependent special slot which
|
||
|
|
should be used to store <var>bounds</var>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fLOAD_005fRETURNED_005fBOUNDS"></a>Target Hook: <em>rtx</em> <strong>TARGET_LOAD_RETURNED_BOUNDS</strong> <em>(rtx <var>slot</var>)</em></dt>
|
||
|
|
<dd><p>This hook is used by expand pass to emit insn to load bounds
|
||
|
|
returned by function call in <var>slot</var>. Hook returns RTX holding
|
||
|
|
loaded bounds.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fSTORE_005fRETURNED_005fBOUNDS"></a>Target Hook: <em>void</em> <strong>TARGET_STORE_RETURNED_BOUNDS</strong> <em>(rtx <var>slot</var>, rtx <var>bounds</var>)</em></dt>
|
||
|
|
<dd><p>This hook is used by expand pass to emit insn to store <var>bounds</var>
|
||
|
|
returned by function call into <var>slot</var>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fCHKP_005fFUNCTION_005fVALUE_005fBOUNDS"></a>Target Hook: <em>rtx</em> <strong>TARGET_CHKP_FUNCTION_VALUE_BOUNDS</strong> <em>(const_tree <var>ret_type</var>, const_tree <var>fn_decl_or_type</var>, bool <var>outgoing</var>)</em></dt>
|
||
|
|
<dd><p>Define this to return an RTX representing the place where a function
|
||
|
|
returns bounds for returned pointers. Arguments meaning is similar to
|
||
|
|
<code>TARGET_FUNCTION_VALUE</code>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl>
|
||
|
|
<dt><a name="index-TARGET_005fSETUP_005fINCOMING_005fVARARG_005fBOUNDS"></a>Target Hook: <em>void</em> <strong>TARGET_SETUP_INCOMING_VARARG_BOUNDS</strong> <em>(cumulative_args_t <var>args_so_far</var>, machine_mode <var>mode</var>, tree <var>type</var>, int *<var>pretend_args_size</var>, int <var>second_time</var>)</em></dt>
|
||
|
|
<dd><p>Use it to store bounds for anonymous register arguments stored
|
||
|
|
into the stack. Arguments meaning is similar to
|
||
|
|
<code>TARGET_SETUP_INCOMING_VARARGS</code>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<div class="header">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Trampolines.html#Trampolines" accesskey="n" rel="next">Trampolines</a>, Previous: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="p" rel="prev">Stack and Calling</a>, Up: <a href="Target-Macros.html#Target-Macros" accesskey="u" rel="up">Target Macros</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|