aarch64-linux-gnu-5.1/share/doc/gccint/Frame-Layout.html - toolchains/linux-x86/gcc - Git at Google

 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <!-- Copyright (C) 1988-2015 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 5.2, http://www.gnu.org/software/texinfo/ -->
 <head>
 <title>GNU Compiler Collection (GCC) Internals: Frame Layout</title>

 <meta name="description" content="GNU Compiler Collection (GCC) Internals: Frame Layout">
 <meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Frame Layout">
 <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="Stack-and-Calling.html#Stack-and-Calling" rel="up" title="Stack and Calling">
 <link href="Exception-Handling.html#Exception-Handling" rel="next" title="Exception Handling">
 <link href="Stack-and-Calling.html#Stack-and-Calling" rel="prev" title="Stack and Calling">
 <style type="text/css">
 <!--
 a.summary-letter {text-decoration: none}
 blockquote.smallquotation {font-size: smaller}
 div.display {margin-left: 3.2em}
 div.example {margin-left: 3.2em}
 div.indentedblock {margin-left: 3.2em}
 div.lisp {margin-left: 3.2em}
 div.smalldisplay {margin-left: 3.2em}
 div.smallexample {margin-left: 3.2em}
 div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
 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.nocodebreak {white-space:nowrap}
 span.nolinebreak {white-space:nowrap}
 span.roman {font-family:serif; font-weight:normal}
 span.sansserif {font-family:sans-serif; font-weight:normal}
 ul.no-bullet {list-style: none}
 -->
 </style>


 </head>

 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
 <a name="Frame-Layout"></a>
 <div class="header">
 <p>
 Next: <a href="Exception-Handling.html#Exception-Handling" accesskey="n" rel="next">Exception Handling</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="Basic-Stack-Layout"></a>
 <h4 class="subsection">17.9.1 Basic Stack Layout</h4>
 <a name="index-stack-frame-layout"></a>
 <a name="index-frame-layout"></a>

 <p>Here is the basic stack layout.
 </p>
 <dl>
 <dt><a name="index-STACK_005fGROWS_005fDOWNWARD"></a>Macro: <strong>STACK_GROWS_DOWNWARD</strong></dt>
 <dd><p>Define this macro if pushing a word onto the stack moves the stack
 pointer to a smaller address.
 </p>
 <p>When we say, &ldquo;define this macro if &hellip;&rdquo;, it means that the
 compiler checks this macro only with <code>#ifdef</code> so the precise
 definition used does not matter.
 </p></dd></dl>

 <dl>
 <dt><a name="index-STACK_005fPUSH_005fCODE"></a>Macro: <strong>STACK_PUSH_CODE</strong></dt>
 <dd><p>This macro defines the operation used when something is pushed
 on the stack.  In RTL, a push operation will be
 <code>(set (mem (STACK_PUSH_CODE (reg sp))) &hellip;)</code>
 </p>
 <p>The choices are <code>PRE_DEC</code>, <code>POST_DEC</code>, <code>PRE_INC</code>,
 and <code>POST_INC</code>.  Which of these is correct depends on
 the stack direction and on whether the stack pointer points
 to the last item on the stack or whether it points to the
 space for the next item on the stack.
 </p>
 <p>The default is <code>PRE_DEC</code> when <code>STACK_GROWS_DOWNWARD</code> is
 defined, which is almost always right, and <code>PRE_INC</code> otherwise,
 which is often wrong.
 </p></dd></dl>

 <dl>
 <dt><a name="index-FRAME_005fGROWS_005fDOWNWARD"></a>Macro: <strong>FRAME_GROWS_DOWNWARD</strong></dt>
 <dd><p>Define this macro to nonzero value if the addresses of local variable slots
 are at negative offsets from the frame pointer.
 </p></dd></dl>

 <dl>
 <dt><a name="index-ARGS_005fGROW_005fDOWNWARD"></a>Macro: <strong>ARGS_GROW_DOWNWARD</strong></dt>
 <dd><p>Define this macro if successive arguments to a function occupy decreasing
 addresses on the stack.
 </p></dd></dl>

 <dl>
 <dt><a name="index-STARTING_005fFRAME_005fOFFSET"></a>Macro: <strong>STARTING_FRAME_OFFSET</strong></dt>
 <dd><p>Offset from the frame pointer to the first local variable slot to be allocated.
 </p>
 <p>If <code>FRAME_GROWS_DOWNWARD</code>, find the next slot&rsquo;s offset by
 subtracting the first slot&rsquo;s length from <code>STARTING_FRAME_OFFSET</code>.
 Otherwise, it is found by adding the length of the first slot to the
 value <code>STARTING_FRAME_OFFSET</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-STACK_005fALIGNMENT_005fNEEDED"></a>Macro: <strong>STACK_ALIGNMENT_NEEDED</strong></dt>
 <dd><p>Define to zero to disable final alignment of the stack during reload.
 The nonzero default for this macro is suitable for most ports.
 </p>
 <p>On ports where <code>STARTING_FRAME_OFFSET</code> is nonzero or where there
 is a register save block following the local block that doesn&rsquo;t require
 alignment to <code>STACK_BOUNDARY</code>, it may be beneficial to disable
 stack alignment and do it in the backend.
 </p></dd></dl>

 <dl>
 <dt><a name="index-STACK_005fPOINTER_005fOFFSET"></a>Macro: <strong>STACK_POINTER_OFFSET</strong></dt>
 <dd><p>Offset from the stack pointer register to the first location at which
 outgoing arguments are placed.  If not specified, the default value of
 zero is used.  This is the proper value for most machines.
 </p>
 <p>If <code>ARGS_GROW_DOWNWARD</code>, this is the offset to the location above
 the first location at which outgoing arguments are placed.
 </p></dd></dl>

 <dl>
 <dt><a name="index-FIRST_005fPARM_005fOFFSET"></a>Macro: <strong>FIRST_PARM_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
 <dd><p>Offset from the argument pointer register to the first argument&rsquo;s
 address.  On some machines it may depend on the data type of the
 function.
 </p>
 <p>If <code>ARGS_GROW_DOWNWARD</code>, this is the offset to the location above
 the first argument&rsquo;s address.
 </p></dd></dl>

 <dl>
 <dt><a name="index-STACK_005fDYNAMIC_005fOFFSET"></a>Macro: <strong>STACK_DYNAMIC_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
 <dd><p>Offset from the stack pointer register to an item dynamically allocated
 on the stack, e.g., by <code>alloca</code>.
 </p>
 <p>The default value for this macro is <code>STACK_POINTER_OFFSET</code> plus the
 length of the outgoing arguments.  The default is correct for most
 machines.  See <samp>function.c</samp> for details.
 </p></dd></dl>

 <dl>
 <dt><a name="index-INITIAL_005fFRAME_005fADDRESS_005fRTX"></a>Macro: <strong>INITIAL_FRAME_ADDRESS_RTX</strong></dt>
 <dd><p>A C expression whose value is RTL representing the address of the initial
 stack frame. This address is passed to <code>RETURN_ADDR_RTX</code> and
 <code>DYNAMIC_CHAIN_ADDRESS</code>.  If you don&rsquo;t define this macro, a reasonable
 default value will be used.  Define this macro in order to make frame pointer
 elimination work in the presence of <code>__builtin_frame_address (count)</code> and
 <code>__builtin_return_address (count)</code> for <code>count</code> not equal to zero.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DYNAMIC_005fCHAIN_005fADDRESS"></a>Macro: <strong>DYNAMIC_CHAIN_ADDRESS</strong> <em>(<var>frameaddr</var>)</em></dt>
 <dd><p>A C expression whose value is RTL representing the address in a stack
 frame where the pointer to the caller&rsquo;s frame is stored.  Assume that
 <var>frameaddr</var> is an RTL expression for the address of the stack frame
 itself.
 </p>
 <p>If you don&rsquo;t define this macro, the default is to return the value
 of <var>frameaddr</var>&mdash;that is, the stack frame address is also the
 address of the stack word that points to the previous frame.
 </p></dd></dl>

 <dl>
 <dt><a name="index-SETUP_005fFRAME_005fADDRESSES"></a>Macro: <strong>SETUP_FRAME_ADDRESSES</strong></dt>
 <dd><p>If defined, a C expression that produces the machine-specific code to
 setup the stack so that arbitrary frames can be accessed.  For example,
 on the SPARC, we must flush all of the register windows to the stack
 before we can access arbitrary stack frames.  You will seldom need to
 define this macro.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fBUILTIN_005fSETJMP_005fFRAME_005fVALUE"></a>Target Hook: <em>rtx</em> <strong>TARGET_BUILTIN_SETJMP_FRAME_VALUE</strong> <em>(void)</em></dt>
 <dd><p>This target hook should return an rtx that is used to store
 the address of the current frame into the built in <code>setjmp</code> buffer.
 The default value, <code>virtual_stack_vars_rtx</code>, is correct for most
 machines.  One reason you may need to define this target hook is if
 <code>hard_frame_pointer_rtx</code> is the appropriate value on your machine.
 </p></dd></dl>

 <dl>
 <dt><a name="index-FRAME_005fADDR_005fRTX"></a>Macro: <strong>FRAME_ADDR_RTX</strong> <em>(<var>frameaddr</var>)</em></dt>
 <dd><p>A C expression whose value is RTL representing the value of the frame
 address for the current frame.  <var>frameaddr</var> is the frame pointer
 of the current frame.  This is used for __builtin_frame_address.
 You need only define this macro if the frame address is not the same
 as the frame pointer.  Most machines do not need to define it.
 </p></dd></dl>

 <dl>
 <dt><a name="index-RETURN_005fADDR_005fRTX"></a>Macro: <strong>RETURN_ADDR_RTX</strong> <em>(<var>count</var>, <var>frameaddr</var>)</em></dt>
 <dd><p>A C expression whose value is RTL representing the value of the return
 address for the frame <var>count</var> steps up from the current frame, after
 the prologue.  <var>frameaddr</var> is the frame pointer of the <var>count</var>
 frame, or the frame pointer of the <var>count</var> - 1 frame if
 <code>RETURN_ADDR_IN_PREVIOUS_FRAME</code> is nonzero.
 </p>
 <p>The value of the expression must always be the correct address when
 <var>count</var> is zero, but may be <code>NULL_RTX</code> if there is no way to
 determine the return address of other frames.
 </p></dd></dl>

 <dl>
 <dt><a name="index-RETURN_005fADDR_005fIN_005fPREVIOUS_005fFRAME"></a>Macro: <strong>RETURN_ADDR_IN_PREVIOUS_FRAME</strong></dt>
 <dd><p>Define this macro to nonzero value if the return address of a particular
 stack frame is accessed from the frame pointer of the previous stack
 frame.  The zero default for this macro is suitable for most ports.
 </p></dd></dl>

 <dl>
 <dt><a name="index-INCOMING_005fRETURN_005fADDR_005fRTX"></a>Macro: <strong>INCOMING_RETURN_ADDR_RTX</strong></dt>
 <dd><p>A C expression whose value is RTL representing the location of the
 incoming return address at the beginning of any function, before the
 prologue.  This RTL is either a <code>REG</code>, indicating that the return
 value is saved in &lsquo;<samp>REG</samp>&rsquo;, or a <code>MEM</code> representing a location in
 the stack.
 </p>
 <p>You only need to define this macro if you want to support call frame
 debugging information like that provided by DWARF 2.
 </p>
 <p>If this RTL is a <code>REG</code>, you should also define
 <code>DWARF_FRAME_RETURN_COLUMN</code> to <code>DWARF_FRAME_REGNUM (REGNO)</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DWARF_005fALT_005fFRAME_005fRETURN_005fCOLUMN"></a>Macro: <strong>DWARF_ALT_FRAME_RETURN_COLUMN</strong></dt>
 <dd><p>A C expression whose value is an integer giving a DWARF 2 column
 number that may be used as an alternative return column.  The column
 must not correspond to any gcc hard register (that is, it must not
 be in the range of <code>DWARF_FRAME_REGNUM</code>).
 </p>
 <p>This macro can be useful if <code>DWARF_FRAME_RETURN_COLUMN</code> is set to a
 general register, but an alternative column needs to be used for signal
 frames.  Some targets have also used different frame return columns
 over time.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DWARF_005fZERO_005fREG"></a>Macro: <strong>DWARF_ZERO_REG</strong></dt>
 <dd><p>A C expression whose value is an integer giving a DWARF 2 register
 number that is considered to always have the value zero.  This should
 only be defined if the target has an architected zero register, and
 someone decided it was a good idea to use that register number to
 terminate the stack backtrace.  New ports should avoid this.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fDWARF_005fHANDLE_005fFRAME_005fUNSPEC"></a>Target Hook: <em>void</em> <strong>TARGET_DWARF_HANDLE_FRAME_UNSPEC</strong> <em>(const char *<var>label</var>, rtx <var>pattern</var>, int <var>index</var>)</em></dt>
 <dd><p>This target hook allows the backend to emit frame-related insns that
 contain UNSPECs or UNSPEC_VOLATILEs.  The DWARF 2 call frame debugging
 info engine will invoke it on insns of the form
 </p><div class="smallexample">
 <pre class="smallexample">(set (reg) (unspec [&hellip;] UNSPEC_INDEX))
 </pre></div>
 <p>and
 </p><div class="smallexample">
 <pre class="smallexample">(set (reg) (unspec_volatile [&hellip;] UNSPECV_INDEX)).
 </pre></div>
 <p>to let the backend emit the call frame instructions.  <var>label</var> is
 the CFI label attached to the insn, <var>pattern</var> is the pattern of
 the insn and <var>index</var> is <code>UNSPEC_INDEX</code> or <code>UNSPECV_INDEX</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-INCOMING_005fFRAME_005fSP_005fOFFSET"></a>Macro: <strong>INCOMING_FRAME_SP_OFFSET</strong></dt>
 <dd><p>A C expression whose value is an integer giving the offset, in bytes,
 from the value of the stack pointer register to the top of the stack
 frame at the beginning of any function, before the prologue.  The top of
 the frame is defined to be the value of the stack pointer in the
 previous frame, just before the call instruction.
 </p>
 <p>You only need to define this macro if you want to support call frame
 debugging information like that provided by DWARF 2.
 </p></dd></dl>

 <dl>
 <dt><a name="index-ARG_005fPOINTER_005fCFA_005fOFFSET"></a>Macro: <strong>ARG_POINTER_CFA_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
 <dd><p>A C expression whose value is an integer giving the offset, in bytes,
 from the argument pointer to the canonical frame address (cfa).  The
 final value should coincide with that calculated by
 <code>INCOMING_FRAME_SP_OFFSET</code>.  Which is unfortunately not usable
 during virtual register instantiation.
 </p>
 <p>The default value for this macro is
 <code>FIRST_PARM_OFFSET (fundecl) + crtl-&gt;args.pretend_args_size</code>,
 which is correct for most machines; in general, the arguments are found
 immediately before the stack frame.  Note that this is not the case on
 some targets that save registers into the caller&rsquo;s frame, such as SPARC
 and rs6000, and so such targets need to define this macro.
 </p>
 <p>You only need to define this macro if the default is incorrect, and you
 want to support call frame debugging information like that provided by
 DWARF 2.
 </p></dd></dl>

 <dl>
 <dt><a name="index-FRAME_005fPOINTER_005fCFA_005fOFFSET"></a>Macro: <strong>FRAME_POINTER_CFA_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
 <dd><p>If defined, a C expression whose value is an integer giving the offset
 in bytes from the frame pointer to the canonical frame address (cfa).
 The final value should coincide with that calculated by
 <code>INCOMING_FRAME_SP_OFFSET</code>.
 </p>
 <p>Normally the CFA is calculated as an offset from the argument pointer,
 via <code>ARG_POINTER_CFA_OFFSET</code>, but if the argument pointer is
 variable due to the ABI, this may not be possible.  If this macro is
 defined, it implies that the virtual register instantiation should be
 based on the frame pointer instead of the argument pointer.  Only one
 of <code>FRAME_POINTER_CFA_OFFSET</code> and <code>ARG_POINTER_CFA_OFFSET</code>
 should be defined.
 </p></dd></dl>

 <dl>
 <dt><a name="index-CFA_005fFRAME_005fBASE_005fOFFSET"></a>Macro: <strong>CFA_FRAME_BASE_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
 <dd><p>If defined, a C expression whose value is an integer giving the offset
 in bytes from the canonical frame address (cfa) to the frame base used
 in DWARF 2 debug information.  The default is zero.  A different value
 may reduce the size of debug information on some ports.
 </p></dd></dl>

 <hr>
 <div class="header">
 <p>
 Next: <a href="Exception-Handling.html#Exception-Handling" accesskey="n" rel="next">Exception Handling</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>


 </body>
 </html>
	<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
	<html>
	<!-- Copyright (C) 1988-2015 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 5.2, http://www.gnu.org/software/texinfo/ -->
	<head>
	<title>GNU Compiler Collection (GCC) Internals: Frame Layout</title>

	<meta name="description" content="GNU Compiler Collection (GCC) Internals: Frame Layout">
	<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: Frame Layout">
	<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="Stack-and-Calling.html#Stack-and-Calling" rel="up" title="Stack and Calling">
	<link href="Exception-Handling.html#Exception-Handling" rel="next" title="Exception Handling">
	<link href="Stack-and-Calling.html#Stack-and-Calling" rel="prev" title="Stack and Calling">
	<style type="text/css">
	<!--
	a.summary-letter {text-decoration: none}
	blockquote.smallquotation {font-size: smaller}
	div.display {margin-left: 3.2em}
	div.example {margin-left: 3.2em}
	div.indentedblock {margin-left: 3.2em}
	div.lisp {margin-left: 3.2em}
	div.smalldisplay {margin-left: 3.2em}
	div.smallexample {margin-left: 3.2em}
	div.smallindentedblock {margin-left: 3.2em; font-size: smaller}
	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.nocodebreak {white-space:nowrap}
	span.nolinebreak {white-space:nowrap}
	span.roman {font-family:serif; font-weight:normal}
	span.sansserif {font-family:sans-serif; font-weight:normal}
	ul.no-bullet {list-style: none}
	-->
	</style>


	</head>

	<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
	<a name="Frame-Layout"></a>
	<div class="header">
	<p>
	Next: <a href="Exception-Handling.html#Exception-Handling" accesskey="n" rel="next">Exception Handling</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="Basic-Stack-Layout"></a>
	<h4 class="subsection">17.9.1 Basic Stack Layout</h4>
	<a name="index-stack-frame-layout"></a>
	<a name="index-frame-layout"></a>

	<p>Here is the basic stack layout.
	</p>
	<dl>
	<dt><a name="index-STACK_005fGROWS_005fDOWNWARD"></a>Macro: <strong>STACK_GROWS_DOWNWARD</strong></dt>
	<dd><p>Define this macro if pushing a word onto the stack moves the stack
	pointer to a smaller address.
	</p>
	<p>When we say, “define this macro if …”, it means that the
	compiler checks this macro only with <code>#ifdef</code> so the precise
	definition used does not matter.
	</p></dd></dl>

	<dl>
	<dt><a name="index-STACK_005fPUSH_005fCODE"></a>Macro: <strong>STACK_PUSH_CODE</strong></dt>
	<dd><p>This macro defines the operation used when something is pushed
	on the stack. In RTL, a push operation will be
	<code>(set (mem (STACK_PUSH_CODE (reg sp))) …)</code>
	</p>
	<p>The choices are <code>PRE_DEC</code>, <code>POST_DEC</code>, <code>PRE_INC</code>,
	and <code>POST_INC</code>. Which of these is correct depends on
	the stack direction and on whether the stack pointer points
	to the last item on the stack or whether it points to the
	space for the next item on the stack.
	</p>
	<p>The default is <code>PRE_DEC</code> when <code>STACK_GROWS_DOWNWARD</code> is
	defined, which is almost always right, and <code>PRE_INC</code> otherwise,
	which is often wrong.
	</p></dd></dl>

	<dl>
	<dt><a name="index-FRAME_005fGROWS_005fDOWNWARD"></a>Macro: <strong>FRAME_GROWS_DOWNWARD</strong></dt>
	<dd><p>Define this macro to nonzero value if the addresses of local variable slots
	are at negative offsets from the frame pointer.
	</p></dd></dl>

	<dl>
	<dt><a name="index-ARGS_005fGROW_005fDOWNWARD"></a>Macro: <strong>ARGS_GROW_DOWNWARD</strong></dt>
	<dd><p>Define this macro if successive arguments to a function occupy decreasing
	addresses on the stack.
	</p></dd></dl>

	<dl>
	<dt><a name="index-STARTING_005fFRAME_005fOFFSET"></a>Macro: <strong>STARTING_FRAME_OFFSET</strong></dt>
	<dd><p>Offset from the frame pointer to the first local variable slot to be allocated.
	</p>
	<p>If <code>FRAME_GROWS_DOWNWARD</code>, find the next slot’s offset by
	subtracting the first slot’s length from <code>STARTING_FRAME_OFFSET</code>.
	Otherwise, it is found by adding the length of the first slot to the
	value <code>STARTING_FRAME_OFFSET</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-STACK_005fALIGNMENT_005fNEEDED"></a>Macro: <strong>STACK_ALIGNMENT_NEEDED</strong></dt>
	<dd><p>Define to zero to disable final alignment of the stack during reload.
	The nonzero default for this macro is suitable for most ports.
	</p>
	<p>On ports where <code>STARTING_FRAME_OFFSET</code> is nonzero or where there
	is a register save block following the local block that doesn’t require
	alignment to <code>STACK_BOUNDARY</code>, it may be beneficial to disable
	stack alignment and do it in the backend.
	</p></dd></dl>

	<dl>
	<dt><a name="index-STACK_005fPOINTER_005fOFFSET"></a>Macro: <strong>STACK_POINTER_OFFSET</strong></dt>
	<dd><p>Offset from the stack pointer register to the first location at which
	outgoing arguments are placed. If not specified, the default value of
	zero is used. This is the proper value for most machines.
	</p>
	<p>If <code>ARGS_GROW_DOWNWARD</code>, this is the offset to the location above
	the first location at which outgoing arguments are placed.
	</p></dd></dl>

	<dl>
	<dt><a name="index-FIRST_005fPARM_005fOFFSET"></a>Macro: <strong>FIRST_PARM_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
	<dd><p>Offset from the argument pointer register to the first argument’s
	address. On some machines it may depend on the data type of the
	function.
	</p>
	<p>If <code>ARGS_GROW_DOWNWARD</code>, this is the offset to the location above
	the first argument’s address.
	</p></dd></dl>

	<dl>
	<dt><a name="index-STACK_005fDYNAMIC_005fOFFSET"></a>Macro: <strong>STACK_DYNAMIC_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
	<dd><p>Offset from the stack pointer register to an item dynamically allocated
	on the stack, e.g., by <code>alloca</code>.
	</p>
	<p>The default value for this macro is <code>STACK_POINTER_OFFSET</code> plus the
	length of the outgoing arguments. The default is correct for most
	machines. See <samp>function.c</samp> for details.
	</p></dd></dl>

	<dl>
	<dt><a name="index-INITIAL_005fFRAME_005fADDRESS_005fRTX"></a>Macro: <strong>INITIAL_FRAME_ADDRESS_RTX</strong></dt>
	<dd><p>A C expression whose value is RTL representing the address of the initial
	stack frame. This address is passed to <code>RETURN_ADDR_RTX</code> and
	<code>DYNAMIC_CHAIN_ADDRESS</code>. If you don’t define this macro, a reasonable
	default value will be used. Define this macro in order to make frame pointer
	elimination work in the presence of <code>__builtin_frame_address (count)</code> and
	<code>__builtin_return_address (count)</code> for <code>count</code> not equal to zero.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DYNAMIC_005fCHAIN_005fADDRESS"></a>Macro: <strong>DYNAMIC_CHAIN_ADDRESS</strong> <em>(<var>frameaddr</var>)</em></dt>
	<dd><p>A C expression whose value is RTL representing the address in a stack
	frame where the pointer to the caller’s frame is stored. Assume that
	<var>frameaddr</var> is an RTL expression for the address of the stack frame
	itself.
	</p>
	<p>If you don’t define this macro, the default is to return the value
	of <var>frameaddr</var>—that is, the stack frame address is also the
	address of the stack word that points to the previous frame.
	</p></dd></dl>

	<dl>
	<dt><a name="index-SETUP_005fFRAME_005fADDRESSES"></a>Macro: <strong>SETUP_FRAME_ADDRESSES</strong></dt>
	<dd><p>If defined, a C expression that produces the machine-specific code to
	setup the stack so that arbitrary frames can be accessed. For example,
	on the SPARC, we must flush all of the register windows to the stack
	before we can access arbitrary stack frames. You will seldom need to
	define this macro.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fBUILTIN_005fSETJMP_005fFRAME_005fVALUE"></a>Target Hook: <em>rtx</em> <strong>TARGET_BUILTIN_SETJMP_FRAME_VALUE</strong> <em>(void)</em></dt>
	<dd><p>This target hook should return an rtx that is used to store
	the address of the current frame into the built in <code>setjmp</code> buffer.
	The default value, <code>virtual_stack_vars_rtx</code>, is correct for most
	machines. One reason you may need to define this target hook is if
	<code>hard_frame_pointer_rtx</code> is the appropriate value on your machine.
	</p></dd></dl>

	<dl>
	<dt><a name="index-FRAME_005fADDR_005fRTX"></a>Macro: <strong>FRAME_ADDR_RTX</strong> <em>(<var>frameaddr</var>)</em></dt>
	<dd><p>A C expression whose value is RTL representing the value of the frame
	address for the current frame. <var>frameaddr</var> is the frame pointer
	of the current frame. This is used for __builtin_frame_address.
	You need only define this macro if the frame address is not the same
	as the frame pointer. Most machines do not need to define it.
	</p></dd></dl>

	<dl>
	<dt><a name="index-RETURN_005fADDR_005fRTX"></a>Macro: <strong>RETURN_ADDR_RTX</strong> <em>(<var>count</var>, <var>frameaddr</var>)</em></dt>
	<dd><p>A C expression whose value is RTL representing the value of the return
	address for the frame <var>count</var> steps up from the current frame, after
	the prologue. <var>frameaddr</var> is the frame pointer of the <var>count</var>
	frame, or the frame pointer of the <var>count</var> - 1 frame if
	<code>RETURN_ADDR_IN_PREVIOUS_FRAME</code> is nonzero.
	</p>
	<p>The value of the expression must always be the correct address when
	<var>count</var> is zero, but may be <code>NULL_RTX</code> if there is no way to
	determine the return address of other frames.
	</p></dd></dl>

	<dl>
	<dt><a name="index-RETURN_005fADDR_005fIN_005fPREVIOUS_005fFRAME"></a>Macro: <strong>RETURN_ADDR_IN_PREVIOUS_FRAME</strong></dt>
	<dd><p>Define this macro to nonzero value if the return address of a particular
	stack frame is accessed from the frame pointer of the previous stack
	frame. The zero default for this macro is suitable for most ports.
	</p></dd></dl>

	<dl>
	<dt><a name="index-INCOMING_005fRETURN_005fADDR_005fRTX"></a>Macro: <strong>INCOMING_RETURN_ADDR_RTX</strong></dt>
	<dd><p>A C expression whose value is RTL representing the location of the
	incoming return address at the beginning of any function, before the
	prologue. This RTL is either a <code>REG</code>, indicating that the return
	value is saved in ‘<samp>REG</samp>’, or a <code>MEM</code> representing a location in
	the stack.
	</p>
	<p>You only need to define this macro if you want to support call frame
	debugging information like that provided by DWARF 2.
	</p>
	<p>If this RTL is a <code>REG</code>, you should also define
	<code>DWARF_FRAME_RETURN_COLUMN</code> to <code>DWARF_FRAME_REGNUM (REGNO)</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DWARF_005fALT_005fFRAME_005fRETURN_005fCOLUMN"></a>Macro: <strong>DWARF_ALT_FRAME_RETURN_COLUMN</strong></dt>
	<dd><p>A C expression whose value is an integer giving a DWARF 2 column
	number that may be used as an alternative return column. The column
	must not correspond to any gcc hard register (that is, it must not
	be in the range of <code>DWARF_FRAME_REGNUM</code>).
	</p>
	<p>This macro can be useful if <code>DWARF_FRAME_RETURN_COLUMN</code> is set to a
	general register, but an alternative column needs to be used for signal
	frames. Some targets have also used different frame return columns
	over time.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DWARF_005fZERO_005fREG"></a>Macro: <strong>DWARF_ZERO_REG</strong></dt>
	<dd><p>A C expression whose value is an integer giving a DWARF 2 register
	number that is considered to always have the value zero. This should
	only be defined if the target has an architected zero register, and
	someone decided it was a good idea to use that register number to
	terminate the stack backtrace. New ports should avoid this.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fDWARF_005fHANDLE_005fFRAME_005fUNSPEC"></a>Target Hook: <em>void</em> <strong>TARGET_DWARF_HANDLE_FRAME_UNSPEC</strong> <em>(const char *<var>label</var>, rtx <var>pattern</var>, int <var>index</var>)</em></dt>
	<dd><p>This target hook allows the backend to emit frame-related insns that
	contain UNSPECs or UNSPEC_VOLATILEs. The DWARF 2 call frame debugging
	info engine will invoke it on insns of the form
	</p><div class="smallexample">
	<pre class="smallexample">(set (reg) (unspec […] UNSPEC_INDEX))
	</pre></div>
	<p>and
	</p><div class="smallexample">
	<pre class="smallexample">(set (reg) (unspec_volatile […] UNSPECV_INDEX)).
	</pre></div>
	<p>to let the backend emit the call frame instructions. <var>label</var> is
	the CFI label attached to the insn, <var>pattern</var> is the pattern of
	the insn and <var>index</var> is <code>UNSPEC_INDEX</code> or <code>UNSPECV_INDEX</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-INCOMING_005fFRAME_005fSP_005fOFFSET"></a>Macro: <strong>INCOMING_FRAME_SP_OFFSET</strong></dt>
	<dd><p>A C expression whose value is an integer giving the offset, in bytes,
	from the value of the stack pointer register to the top of the stack
	frame at the beginning of any function, before the prologue. The top of
	the frame is defined to be the value of the stack pointer in the
	previous frame, just before the call instruction.
	</p>
	<p>You only need to define this macro if you want to support call frame
	debugging information like that provided by DWARF 2.
	</p></dd></dl>

	<dl>
	<dt><a name="index-ARG_005fPOINTER_005fCFA_005fOFFSET"></a>Macro: <strong>ARG_POINTER_CFA_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
	<dd><p>A C expression whose value is an integer giving the offset, in bytes,
	from the argument pointer to the canonical frame address (cfa). The
	final value should coincide with that calculated by
	<code>INCOMING_FRAME_SP_OFFSET</code>. Which is unfortunately not usable
	during virtual register instantiation.
	</p>
	<p>The default value for this macro is
	<code>FIRST_PARM_OFFSET (fundecl) + crtl->args.pretend_args_size</code>,
	which is correct for most machines; in general, the arguments are found
	immediately before the stack frame. Note that this is not the case on
	some targets that save registers into the caller’s frame, such as SPARC
	and rs6000, and so such targets need to define this macro.
	</p>
	<p>You only need to define this macro if the default is incorrect, and you
	want to support call frame debugging information like that provided by
	DWARF 2.
	</p></dd></dl>

	<dl>
	<dt><a name="index-FRAME_005fPOINTER_005fCFA_005fOFFSET"></a>Macro: <strong>FRAME_POINTER_CFA_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
	<dd><p>If defined, a C expression whose value is an integer giving the offset
	in bytes from the frame pointer to the canonical frame address (cfa).
	The final value should coincide with that calculated by
	<code>INCOMING_FRAME_SP_OFFSET</code>.
	</p>
	<p>Normally the CFA is calculated as an offset from the argument pointer,
	via <code>ARG_POINTER_CFA_OFFSET</code>, but if the argument pointer is
	variable due to the ABI, this may not be possible. If this macro is
	defined, it implies that the virtual register instantiation should be
	based on the frame pointer instead of the argument pointer. Only one
	of <code>FRAME_POINTER_CFA_OFFSET</code> and <code>ARG_POINTER_CFA_OFFSET</code>
	should be defined.
	</p></dd></dl>

	<dl>
	<dt><a name="index-CFA_005fFRAME_005fBASE_005fOFFSET"></a>Macro: <strong>CFA_FRAME_BASE_OFFSET</strong> <em>(<var>fundecl</var>)</em></dt>
	<dd><p>If defined, a C expression whose value is an integer giving the offset
	in bytes from the canonical frame address (cfa) to the frame base used
	in DWARF 2 debug information. The default is zero. A different value
	may reduce the size of debug information on some ports.
	</p></dd></dl>

	<hr>
	<div class="header">
	<p>
	Next: <a href="Exception-Handling.html#Exception-Handling" accesskey="n" rel="next">Exception Handling</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>



	</body>
	</html>