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 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
 <a name="Stack-Arguments"></a>
 <div class="header">
 <p>
 Next: <a href="Register-Arguments.html#Register-Arguments" accesskey="n" rel="next">Register Arguments</a>, Previous: <a href="Elimination.html#Elimination" accesskey="p" rel="prev">Elimination</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</a> &nbsp; [<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="Passing-Function-Arguments-on-the-Stack"></a>
 <h4 class="subsection">17.9.6 Passing Function Arguments on the Stack</h4>
 <a name="index-arguments-on-stack"></a>
 <a name="index-stack-arguments"></a>

 <p>The macros in this section control how arguments are passed
 on the stack.  See the following section for other macros that
 control passing certain arguments in registers.
 </p>
 <dl>
 <dt><a name="index-TARGET_005fPROMOTE_005fPROTOTYPES"></a>Target Hook: <em>bool</em> <strong>TARGET_PROMOTE_PROTOTYPES</strong> <em>(const_tree <var>fntype</var>)</em></dt>
 <dd><p>This target hook returns <code>true</code> if an argument declared in a
 prototype as an integral type smaller than <code>int</code> should actually be
 passed as an <code>int</code>.  In addition to avoiding errors in certain
 cases of mismatch, it also makes for better code on certain machines.
 The default is to not promote prototypes.
 </p></dd></dl>

 <dl>
 <dt><a name="index-PUSH_005fARGS"></a>Macro: <strong>PUSH_ARGS</strong></dt>
 <dd><p>A C expression.  If nonzero, push insns will be used to pass
 outgoing arguments.
 If the target machine does not have a push instruction, set it to zero.
 That directs GCC to use an alternate strategy: to
 allocate the entire argument block and then store the arguments into
 it.  When <code>PUSH_ARGS</code> is nonzero, <code>PUSH_ROUNDING</code> must be defined too.
 </p></dd></dl>

 <dl>
 <dt><a name="index-PUSH_005fARGS_005fREVERSED"></a>Macro: <strong>PUSH_ARGS_REVERSED</strong></dt>
 <dd><p>A C expression.  If nonzero, function arguments will be evaluated from
 last to first, rather than from first to last.  If this macro is not
 defined, it defaults to <code>PUSH_ARGS</code> on targets where the stack
 and args grow in opposite directions, and 0 otherwise.
 </p></dd></dl>

 <dl>
 <dt><a name="index-PUSH_005fROUNDING"></a>Macro: <strong>PUSH_ROUNDING</strong> <em>(<var>npushed</var>)</em></dt>
 <dd><p>A C expression that is the number of bytes actually pushed onto the
 stack when an instruction attempts to push <var>npushed</var> bytes.
 </p>
 <p>On some machines, the definition
 </p>
 <div class="smallexample">
 <pre class="smallexample">#define PUSH_ROUNDING(BYTES) (BYTES)
 </pre></div>

 <p>will suffice.  But on other machines, instructions that appear
 to push one byte actually push two bytes in an attempt to maintain
 alignment.  Then the definition should be
 </p>
 <div class="smallexample">
 <pre class="smallexample">#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) &amp; ~1)
 </pre></div>

 <p>If the value of this macro has a type, it should be an unsigned type.
 </p></dd></dl>

 <a name="index-outgoing_005fargs_005fsize"></a>
 <a name="index-crtl_002d_003eoutgoing_005fargs_005fsize"></a>
 <dl>
 <dt><a name="index-ACCUMULATE_005fOUTGOING_005fARGS"></a>Macro: <strong>ACCUMULATE_OUTGOING_ARGS</strong></dt>
 <dd><p>A C expression.  If nonzero, the maximum amount of space required for outgoing arguments
 will be computed and placed into
 <code>crtl-&gt;outgoing_args_size</code>.  No space will be pushed
 onto the stack for each call; instead, the function prologue should
 increase the stack frame size by this amount.
 </p>
 <p>Setting both <code>PUSH_ARGS</code> and <code>ACCUMULATE_OUTGOING_ARGS</code>
 is not proper.
 </p></dd></dl>

 <dl>
 <dt><a name="index-REG_005fPARM_005fSTACK_005fSPACE"></a>Macro: <strong>REG_PARM_STACK_SPACE</strong> <em>(<var>fndecl</var>)</em></dt>
 <dd><p>Define this macro if functions should assume that stack space has been
 allocated for arguments even when their values are passed in
 registers.
 </p>
 <p>The value of this macro is the size, in bytes, of the area reserved for
 arguments passed in registers for the function represented by <var>fndecl</var>,
 which can be zero if GCC is calling a library function.
 The argument <var>fndecl</var> can be the FUNCTION_DECL, or the type itself
 of the function.
 </p>
 <p>This space can be allocated by the caller, or be a part of the
 machine-dependent stack frame: <code>OUTGOING_REG_PARM_STACK_SPACE</code> says
 which.
 </p></dd></dl>

 <dl>
 <dt><a name="index-INCOMING_005fREG_005fPARM_005fSTACK_005fSPACE"></a>Macro: <strong>INCOMING_REG_PARM_STACK_SPACE</strong> <em>(<var>fndecl</var>)</em></dt>
 <dd><p>Like <code>REG_PARM_STACK_SPACE</code>, but for incoming register arguments.
 Define this macro if space guaranteed when compiling a function body
 is different to space required when making a call, a situation that
 can arise with K&amp;R style function definitions.
 </p></dd></dl>

 <dl>
 <dt><a name="index-OUTGOING_005fREG_005fPARM_005fSTACK_005fSPACE"></a>Macro: <strong>OUTGOING_REG_PARM_STACK_SPACE</strong> <em>(<var>fntype</var>)</em></dt>
 <dd><p>Define this to a nonzero value if it is the responsibility of the
 caller to allocate the area reserved for arguments passed in registers
 when calling a function of <var>fntype</var>.  <var>fntype</var> may be NULL
 if the function called is a library function.
 </p>
 <p>If <code>ACCUMULATE_OUTGOING_ARGS</code> is defined, this macro controls
 whether the space for these arguments counts in the value of
 <code>crtl-&gt;outgoing_args_size</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-STACK_005fPARMS_005fIN_005fREG_005fPARM_005fAREA"></a>Macro: <strong>STACK_PARMS_IN_REG_PARM_AREA</strong></dt>
 <dd><p>Define this macro if <code>REG_PARM_STACK_SPACE</code> is defined, but the
 stack parameters don&rsquo;t skip the area specified by it.
 </p>
 <p>Normally, when a parameter is not passed in registers, it is placed on the
 stack beyond the <code>REG_PARM_STACK_SPACE</code> area.  Defining this macro
 suppresses this behavior and causes the parameter to be passed on the
 stack in its natural location.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fRETURN_005fPOPS_005fARGS"></a>Target Hook: <em>int</em> <strong>TARGET_RETURN_POPS_ARGS</strong> <em>(tree <var>fundecl</var>, tree <var>funtype</var>, int <var>size</var>)</em></dt>
 <dd><p>This target hook returns the number of bytes of its own arguments that
 a function pops on returning, or 0 if the function pops no arguments
 and the caller must therefore pop them all after the function returns.
 </p>
 <p><var>fundecl</var> is a C variable whose value is a tree node that describes
 the function in question.  Normally it is a node of type
 <code>FUNCTION_DECL</code> that describes the declaration of the function.
 From this you can obtain the <code>DECL_ATTRIBUTES</code> of the function.
 </p>
 <p><var>funtype</var> is a C variable whose value is a tree node that
 describes the function in question.  Normally it is a node of type
 <code>FUNCTION_TYPE</code> that describes the data type of the function.
 From this it is possible to obtain the data types of the value and
 arguments (if known).
 </p>
 <p>When a call to a library function is being considered, <var>fundecl</var>
 will contain an identifier node for the library function.  Thus, if
 you need to distinguish among various library functions, you can do so
 by their names.  Note that &ldquo;library function&rdquo; in this context means
 a function used to perform arithmetic, whose name is known specially
 in the compiler and was not mentioned in the C code being compiled.
 </p>
 <p><var>size</var> is the number of bytes of arguments passed on the
 stack.  If a variable number of bytes is passed, it is zero, and
 argument popping will always be the responsibility of the calling function.
 </p>
 <p>On the VAX, all functions always pop their arguments, so the definition
 of this macro is <var>size</var>.  On the 68000, using the standard
 calling convention, no functions pop their arguments, so the value of
 the macro is always 0 in this case.  But an alternative calling
 convention is available in which functions that take a fixed number of
 arguments pop them but other functions (such as <code>printf</code>) pop
 nothing (the caller pops all).  When this convention is in use,
 <var>funtype</var> is examined to determine whether a function takes a fixed
 number of arguments.
 </p></dd></dl>

 <dl>
 <dt><a name="index-CALL_005fPOPS_005fARGS"></a>Macro: <strong>CALL_POPS_ARGS</strong> <em>(<var>cum</var>)</em></dt>
 <dd><p>A C expression that should indicate the number of bytes a call sequence
 pops off the stack.  It is added to the value of <code>RETURN_POPS_ARGS</code>
 when compiling a function call.
 </p>
 <p><var>cum</var> is the variable in which all arguments to the called function
 have been accumulated.
 </p>
 <p>On certain architectures, such as the SH5, a call trampoline is used
 that pops certain registers off the stack, depending on the arguments
 that have been passed to the function.  Since this is a property of the
 call site, not of the called function, <code>RETURN_POPS_ARGS</code> is not
 appropriate.
 </p></dd></dl>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Register-Arguments.html#Register-Arguments" accesskey="n" rel="next">Register Arguments</a>, Previous: <a href="Elimination.html#Elimination" accesskey="p" rel="prev">Elimination</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</a> &nbsp; [<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>
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	<a name="Stack-Arguments"></a>
	<div class="header">
	<p>
	Next: <a href="Register-Arguments.html#Register-Arguments" accesskey="n" rel="next">Register Arguments</a>, Previous: <a href="Elimination.html#Elimination" accesskey="p" rel="prev">Elimination</a>, Up: <a href="Stack-and-Calling.html#Stack-and-Calling" accesskey="u" rel="up">Stack and Calling</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="Passing-Function-Arguments-on-the-Stack"></a>
	<h4 class="subsection">17.9.6 Passing Function Arguments on the Stack</h4>
	<a name="index-arguments-on-stack"></a>
	<a name="index-stack-arguments"></a>

	<p>The macros in this section control how arguments are passed
	on the stack. See the following section for other macros that
	control passing certain arguments in registers.
	</p>
	<dl>
	<dt><a name="index-TARGET_005fPROMOTE_005fPROTOTYPES"></a>Target Hook: <em>bool</em> <strong>TARGET_PROMOTE_PROTOTYPES</strong> <em>(const_tree <var>fntype</var>)</em></dt>
	<dd><p>This target hook returns <code>true</code> if an argument declared in a
	prototype as an integral type smaller than <code>int</code> should actually be
	passed as an <code>int</code>. In addition to avoiding errors in certain
	cases of mismatch, it also makes for better code on certain machines.
	The default is to not promote prototypes.
	</p></dd></dl>

	<dl>
	<dt><a name="index-PUSH_005fARGS"></a>Macro: <strong>PUSH_ARGS</strong></dt>
	<dd><p>A C expression. If nonzero, push insns will be used to pass
	outgoing arguments.
	If the target machine does not have a push instruction, set it to zero.
	That directs GCC to use an alternate strategy: to
	allocate the entire argument block and then store the arguments into
	it. When <code>PUSH_ARGS</code> is nonzero, <code>PUSH_ROUNDING</code> must be defined too.
	</p></dd></dl>

	<dl>
	<dt><a name="index-PUSH_005fARGS_005fREVERSED"></a>Macro: <strong>PUSH_ARGS_REVERSED</strong></dt>
	<dd><p>A C expression. If nonzero, function arguments will be evaluated from
	last to first, rather than from first to last. If this macro is not
	defined, it defaults to <code>PUSH_ARGS</code> on targets where the stack
	and args grow in opposite directions, and 0 otherwise.
	</p></dd></dl>

	<dl>
	<dt><a name="index-PUSH_005fROUNDING"></a>Macro: <strong>PUSH_ROUNDING</strong> <em>(<var>npushed</var>)</em></dt>
	<dd><p>A C expression that is the number of bytes actually pushed onto the
	stack when an instruction attempts to push <var>npushed</var> bytes.
	</p>
	<p>On some machines, the definition
	</p>
	<div class="smallexample">
	<pre class="smallexample">#define PUSH_ROUNDING(BYTES) (BYTES)
	</pre></div>

	<p>will suffice. But on other machines, instructions that appear
	to push one byte actually push two bytes in an attempt to maintain
	alignment. Then the definition should be
	</p>
	<div class="smallexample">
	<pre class="smallexample">#define PUSH_ROUNDING(BYTES) (((BYTES) + 1) & ~1)
	</pre></div>

	<p>If the value of this macro has a type, it should be an unsigned type.
	</p></dd></dl>

	<a name="index-outgoing_005fargs_005fsize"></a>
	<a name="index-crtl_002d_003eoutgoing_005fargs_005fsize"></a>
	<dl>
	<dt><a name="index-ACCUMULATE_005fOUTGOING_005fARGS"></a>Macro: <strong>ACCUMULATE_OUTGOING_ARGS</strong></dt>
	<dd><p>A C expression. If nonzero, the maximum amount of space required for outgoing arguments
	will be computed and placed into
	<code>crtl->outgoing_args_size</code>. No space will be pushed
	onto the stack for each call; instead, the function prologue should
	increase the stack frame size by this amount.
	</p>
	<p>Setting both <code>PUSH_ARGS</code> and <code>ACCUMULATE_OUTGOING_ARGS</code>
	is not proper.
	</p></dd></dl>

	<dl>
	<dt><a name="index-REG_005fPARM_005fSTACK_005fSPACE"></a>Macro: <strong>REG_PARM_STACK_SPACE</strong> <em>(<var>fndecl</var>)</em></dt>
	<dd><p>Define this macro if functions should assume that stack space has been
	allocated for arguments even when their values are passed in
	registers.
	</p>
	<p>The value of this macro is the size, in bytes, of the area reserved for
	arguments passed in registers for the function represented by <var>fndecl</var>,
	which can be zero if GCC is calling a library function.
	The argument <var>fndecl</var> can be the FUNCTION_DECL, or the type itself
	of the function.
	</p>
	<p>This space can be allocated by the caller, or be a part of the
	machine-dependent stack frame: <code>OUTGOING_REG_PARM_STACK_SPACE</code> says
	which.
	</p></dd></dl>

	<dl>
	<dt><a name="index-INCOMING_005fREG_005fPARM_005fSTACK_005fSPACE"></a>Macro: <strong>INCOMING_REG_PARM_STACK_SPACE</strong> <em>(<var>fndecl</var>)</em></dt>
	<dd><p>Like <code>REG_PARM_STACK_SPACE</code>, but for incoming register arguments.
	Define this macro if space guaranteed when compiling a function body
	is different to space required when making a call, a situation that
	can arise with K&R style function definitions.
	</p></dd></dl>

	<dl>
	<dt><a name="index-OUTGOING_005fREG_005fPARM_005fSTACK_005fSPACE"></a>Macro: <strong>OUTGOING_REG_PARM_STACK_SPACE</strong> <em>(<var>fntype</var>)</em></dt>
	<dd><p>Define this to a nonzero value if it is the responsibility of the
	caller to allocate the area reserved for arguments passed in registers
	when calling a function of <var>fntype</var>. <var>fntype</var> may be NULL
	if the function called is a library function.
	</p>
	<p>If <code>ACCUMULATE_OUTGOING_ARGS</code> is defined, this macro controls
	whether the space for these arguments counts in the value of
	<code>crtl->outgoing_args_size</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-STACK_005fPARMS_005fIN_005fREG_005fPARM_005fAREA"></a>Macro: <strong>STACK_PARMS_IN_REG_PARM_AREA</strong></dt>
	<dd><p>Define this macro if <code>REG_PARM_STACK_SPACE</code> is defined, but the
	stack parameters don’t skip the area specified by it.
	</p>
	<p>Normally, when a parameter is not passed in registers, it is placed on the
	stack beyond the <code>REG_PARM_STACK_SPACE</code> area. Defining this macro
	suppresses this behavior and causes the parameter to be passed on the
	stack in its natural location.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fRETURN_005fPOPS_005fARGS"></a>Target Hook: <em>int</em> <strong>TARGET_RETURN_POPS_ARGS</strong> <em>(tree <var>fundecl</var>, tree <var>funtype</var>, int <var>size</var>)</em></dt>
	<dd><p>This target hook returns the number of bytes of its own arguments that
	a function pops on returning, or 0 if the function pops no arguments
	and the caller must therefore pop them all after the function returns.
	</p>
	<p><var>fundecl</var> is a C variable whose value is a tree node that describes
	the function in question. Normally it is a node of type
	<code>FUNCTION_DECL</code> that describes the declaration of the function.
	From this you can obtain the <code>DECL_ATTRIBUTES</code> of the function.
	</p>
	<p><var>funtype</var> is a C variable whose value is a tree node that
	describes the function in question. Normally it is a node of type
	<code>FUNCTION_TYPE</code> that describes the data type of the function.
	From this it is possible to obtain the data types of the value and
	arguments (if known).
	</p>
	<p>When a call to a library function is being considered, <var>fundecl</var>
	will contain an identifier node for the library function. Thus, if
	you need to distinguish among various library functions, you can do so
	by their names. Note that “library function” in this context means
	a function used to perform arithmetic, whose name is known specially
	in the compiler and was not mentioned in the C code being compiled.
	</p>
	<p><var>size</var> is the number of bytes of arguments passed on the
	stack. If a variable number of bytes is passed, it is zero, and
	argument popping will always be the responsibility of the calling function.
	</p>
	<p>On the VAX, all functions always pop their arguments, so the definition
	of this macro is <var>size</var>. On the 68000, using the standard
	calling convention, no functions pop their arguments, so the value of
	the macro is always 0 in this case. But an alternative calling
	convention is available in which functions that take a fixed number of
	arguments pop them but other functions (such as <code>printf</code>) pop
	nothing (the caller pops all). When this convention is in use,
	<var>funtype</var> is examined to determine whether a function takes a fixed
	number of arguments.
	</p></dd></dl>

	<dl>
	<dt><a name="index-CALL_005fPOPS_005fARGS"></a>Macro: <strong>CALL_POPS_ARGS</strong> <em>(<var>cum</var>)</em></dt>
	<dd><p>A C expression that should indicate the number of bytes a call sequence
	pops off the stack. It is added to the value of <code>RETURN_POPS_ARGS</code>
	when compiling a function call.
	</p>
	<p><var>cum</var> is the variable in which all arguments to the called function
	have been accumulated.
	</p>
	<p>On certain architectures, such as the SH5, a call trampoline is used
	that pops certain registers off the stack, depending on the arguments
	that have been passed to the function. Since this is a property of the
	call site, not of the called function, <code>RETURN_POPS_ARGS</code> is not
	appropriate.
	</p></dd></dl>

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