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 <a name="Frame-Registers"></a>
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 <p>
 Next: <a href="Elimination.html#Elimination" accesskey="n" rel="next">Elimination</a>, Previous: <a href="Stack-Checking.html#Stack-Checking" accesskey="p" rel="prev">Stack Checking</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="Registers-That-Address-the-Stack-Frame"></a>
 <h4 class="subsection">17.10.4 Registers That Address the Stack Frame</h4>

 <p>This discusses registers that address the stack frame.
 </p>
 <dl>
 <dt><a name="index-STACK_005fPOINTER_005fREGNUM"></a>Macro: <strong>STACK_POINTER_REGNUM</strong></dt>
 <dd><p>The register number of the stack pointer register, which must also be a
 fixed register according to <code>FIXED_REGISTERS</code>.  On most machines,
 the hardware determines which register this is.
 </p></dd></dl>

 <dl>
 <dt><a name="index-FRAME_005fPOINTER_005fREGNUM"></a>Macro: <strong>FRAME_POINTER_REGNUM</strong></dt>
 <dd><p>The register number of the frame pointer register, which is used to
 access automatic variables in the stack frame.  On some machines, the
 hardware determines which register this is.  On other machines, you can
 choose any register you wish for this purpose.
 </p></dd></dl>

 <dl>
 <dt><a name="index-HARD_005fFRAME_005fPOINTER_005fREGNUM"></a>Macro: <strong>HARD_FRAME_POINTER_REGNUM</strong></dt>
 <dd><p>On some machines the offset between the frame pointer and starting
 offset of the automatic variables is not known until after register
 allocation has been done (for example, because the saved registers are
 between these two locations).  On those machines, define
 <code>FRAME_POINTER_REGNUM</code> the number of a special, fixed register to
 be used internally until the offset is known, and define
 <code>HARD_FRAME_POINTER_REGNUM</code> to be the actual hard register number
 used for the frame pointer.
 </p>
 <p>You should define this macro only in the very rare circumstances when it
 is not possible to calculate the offset between the frame pointer and
 the automatic variables until after register allocation has been
 completed.  When this macro is defined, you must also indicate in your
 definition of <code>ELIMINABLE_REGS</code> how to eliminate
 <code>FRAME_POINTER_REGNUM</code> into either <code>HARD_FRAME_POINTER_REGNUM</code>
 or <code>STACK_POINTER_REGNUM</code>.
 </p>
 <p>Do not define this macro if it would be the same as
 <code>FRAME_POINTER_REGNUM</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-ARG_005fPOINTER_005fREGNUM"></a>Macro: <strong>ARG_POINTER_REGNUM</strong></dt>
 <dd><p>The register number of the arg pointer register, which is used to access
 the function&rsquo;s argument list.  On some machines, this is the same as the
 frame pointer register.  On some machines, the hardware determines which
 register this is.  On other machines, you can choose any register you
 wish for this purpose.  If this is not the same register as the frame
 pointer register, then you must mark it as a fixed register according to
 <code>FIXED_REGISTERS</code>, or arrange to be able to eliminate it
 (see <a href="Elimination.html#Elimination">Elimination</a>).
 </p></dd></dl>

 <dl>
 <dt><a name="index-HARD_005fFRAME_005fPOINTER_005fIS_005fFRAME_005fPOINTER"></a>Macro: <strong>HARD_FRAME_POINTER_IS_FRAME_POINTER</strong></dt>
 <dd><p>Define this to a preprocessor constant that is nonzero if
 <code>hard_frame_pointer_rtx</code> and <code>frame_pointer_rtx</code> should be
 the same.  The default definition is &lsquo;<samp>(HARD_FRAME_POINTER_REGNUM
 == FRAME_POINTER_REGNUM)</samp>&rsquo;; you only need to define this macro if that
 definition is not suitable for use in preprocessor conditionals.
 </p></dd></dl>

 <dl>
 <dt><a name="index-HARD_005fFRAME_005fPOINTER_005fIS_005fARG_005fPOINTER"></a>Macro: <strong>HARD_FRAME_POINTER_IS_ARG_POINTER</strong></dt>
 <dd><p>Define this to a preprocessor constant that is nonzero if
 <code>hard_frame_pointer_rtx</code> and <code>arg_pointer_rtx</code> should be the
 same.  The default definition is &lsquo;<samp>(HARD_FRAME_POINTER_REGNUM ==
 ARG_POINTER_REGNUM)</samp>&rsquo;; you only need to define this macro if that
 definition is not suitable for use in preprocessor conditionals.
 </p></dd></dl>

 <dl>
 <dt><a name="index-RETURN_005fADDRESS_005fPOINTER_005fREGNUM"></a>Macro: <strong>RETURN_ADDRESS_POINTER_REGNUM</strong></dt>
 <dd><p>The register number of the return address pointer register, which is used to
 access the current function&rsquo;s return address from the stack.  On some
 machines, the return address is not at a fixed offset from the frame
 pointer or stack pointer or argument pointer.  This register can be defined
 to point to the return address on the stack, and then be converted by
 <code>ELIMINABLE_REGS</code> into either the frame pointer or stack pointer.
 </p>
 <p>Do not define this macro unless there is no other way to get the return
 address from the stack.
 </p></dd></dl>

 <dl>
 <dt><a name="index-STATIC_005fCHAIN_005fREGNUM"></a>Macro: <strong>STATIC_CHAIN_REGNUM</strong></dt>
 <dt><a name="index-STATIC_005fCHAIN_005fINCOMING_005fREGNUM"></a>Macro: <strong>STATIC_CHAIN_INCOMING_REGNUM</strong></dt>
 <dd><p>Register numbers used for passing a function&rsquo;s static chain pointer.  If
 register windows are used, the register number as seen by the called
 function is <code>STATIC_CHAIN_INCOMING_REGNUM</code>, while the register
 number as seen by the calling function is <code>STATIC_CHAIN_REGNUM</code>.  If
 these registers are the same, <code>STATIC_CHAIN_INCOMING_REGNUM</code> need
 not be defined.
 </p>
 <p>The static chain register need not be a fixed register.
 </p>
 <p>If the static chain is passed in memory, these macros should not be
 defined; instead, the <code>TARGET_STATIC_CHAIN</code> hook should be used.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fSTATIC_005fCHAIN"></a>Target Hook: <em>rtx</em> <strong>TARGET_STATIC_CHAIN</strong> <em>(const_tree <var>fndecl</var>, bool <var>incoming_p</var>)</em></dt>
 <dd><p>This hook replaces the use of <code>STATIC_CHAIN_REGNUM</code> et al for
 targets that may use different static chain locations for different
 nested functions.  This may be required if the target has function
 attributes that affect the calling conventions of the function and
 those calling conventions use different static chain locations.
 </p>
 <p>The default version of this hook uses <code>STATIC_CHAIN_REGNUM</code> et al.
 </p>
 <p>If the static chain is passed in memory, this hook should be used to
 provide rtx giving <code>mem</code> expressions that denote where they are stored.
 Often the <code>mem</code> expression as seen by the caller will be at an offset
 from the stack pointer and the <code>mem</code> expression as seen by the callee
 will be at an offset from the frame pointer.
 <a name="index-stack_005fpointer_005frtx"></a>
 <a name="index-frame_005fpointer_005frtx"></a>
 <a name="index-arg_005fpointer_005frtx"></a>
 The variables <code>stack_pointer_rtx</code>, <code>frame_pointer_rtx</code>, and
 <code>arg_pointer_rtx</code> will have been initialized and should be used
 to refer to those items.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DWARF_005fFRAME_005fREGISTERS"></a>Macro: <strong>DWARF_FRAME_REGISTERS</strong></dt>
 <dd><p>This macro specifies the maximum number of hard registers that can be
 saved in a call frame.  This is used to size data structures used in
 DWARF2 exception handling.
 </p>
 <p>Prior to GCC 3.0, this macro was needed in order to establish a stable
 exception handling ABI in the face of adding new hard registers for ISA
 extensions.  In GCC 3.0 and later, the EH ABI is insulated from changes
 in the number of hard registers.  Nevertheless, this macro can still be
 used to reduce the runtime memory requirements of the exception handling
 routines, which can be substantial if the ISA contains a lot of
 registers that are not call-saved.
 </p>
 <p>If this macro is not defined, it defaults to
 <code>FIRST_PSEUDO_REGISTER</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-PRE_005fGCC3_005fDWARF_005fFRAME_005fREGISTERS"></a>Macro: <strong>PRE_GCC3_DWARF_FRAME_REGISTERS</strong></dt>
 <dd>
 <p>This macro is similar to <code>DWARF_FRAME_REGISTERS</code>, but is provided
 for backward compatibility in pre GCC 3.0 compiled code.
 </p>
 <p>If this macro is not defined, it defaults to
 <code>DWARF_FRAME_REGISTERS</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DWARF_005fREG_005fTO_005fUNWIND_005fCOLUMN"></a>Macro: <strong>DWARF_REG_TO_UNWIND_COLUMN</strong> <em>(<var>regno</var>)</em></dt>
 <dd>
 <p>Define this macro if the target&rsquo;s representation for dwarf registers
 is different than the internal representation for unwind column.
 Given a dwarf register, this macro should return the internal unwind
 column number to use instead.
 </p>
 <p>See the PowerPC&rsquo;s SPE target for an example.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DWARF_005fFRAME_005fREGNUM"></a>Macro: <strong>DWARF_FRAME_REGNUM</strong> <em>(<var>regno</var>)</em></dt>
 <dd>
 <p>Define this macro if the target&rsquo;s representation for dwarf registers
 used in .eh_frame or .debug_frame is different from that used in other
 debug info sections.  Given a GCC hard register number, this macro
 should return the .eh_frame register number.  The default is
 <code>DBX_REGISTER_NUMBER (<var>regno</var>)</code>.
 </p>
 </dd></dl>

 <dl>
 <dt><a name="index-DWARF2_005fFRAME_005fREG_005fOUT"></a>Macro: <strong>DWARF2_FRAME_REG_OUT</strong> <em>(<var>regno</var>, <var>for_eh</var>)</em></dt>
 <dd>
 <p>Define this macro to map register numbers held in the call frame info
 that GCC has collected using <code>DWARF_FRAME_REGNUM</code> to those that
 should be output in .debug_frame (<code><var>for_eh</var></code> is zero) and
 .eh_frame (<code><var>for_eh</var></code> is nonzero).  The default is to
 return <code><var>regno</var></code>.
 </p>
 </dd></dl>

 <dl>
 <dt><a name="index-REG_005fVALUE_005fIN_005fUNWIND_005fCONTEXT"></a>Macro: <strong>REG_VALUE_IN_UNWIND_CONTEXT</strong></dt>
 <dd>
 <p>Define this macro if the target stores register values as
 <code>_Unwind_Word</code> type in unwind context.  It should be defined if
 target register size is larger than the size of <code>void *</code>.  The
 default is to store register values as <code>void *</code> type.
 </p>
 </dd></dl>

 <dl>
 <dt><a name="index-ASSUME_005fEXTENDED_005fUNWIND_005fCONTEXT"></a>Macro: <strong>ASSUME_EXTENDED_UNWIND_CONTEXT</strong></dt>
 <dd>
 <p>Define this macro to be 1 if the target always uses extended unwind
 context with version, args_size and by_value fields.  If it is undefined,
 it will be defined to 1 when <code>REG_VALUE_IN_UNWIND_CONTEXT</code> is
 defined and 0 otherwise.
 </p>
 </dd></dl>

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	<p>
	Next: <a href="Elimination.html#Elimination" accesskey="n" rel="next">Elimination</a>, Previous: <a href="Stack-Checking.html#Stack-Checking" accesskey="p" rel="prev">Stack Checking</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>
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	<hr>
	<a name="Registers-That-Address-the-Stack-Frame"></a>
	<h4 class="subsection">17.10.4 Registers That Address the Stack Frame</h4>

	<p>This discusses registers that address the stack frame.
	</p>
	<dl>
	<dt><a name="index-STACK_005fPOINTER_005fREGNUM"></a>Macro: <strong>STACK_POINTER_REGNUM</strong></dt>
	<dd><p>The register number of the stack pointer register, which must also be a
	fixed register according to <code>FIXED_REGISTERS</code>. On most machines,
	the hardware determines which register this is.
	</p></dd></dl>

	<dl>
	<dt><a name="index-FRAME_005fPOINTER_005fREGNUM"></a>Macro: <strong>FRAME_POINTER_REGNUM</strong></dt>
	<dd><p>The register number of the frame pointer register, which is used to
	access automatic variables in the stack frame. On some machines, the
	hardware determines which register this is. On other machines, you can
	choose any register you wish for this purpose.
	</p></dd></dl>

	<dl>
	<dt><a name="index-HARD_005fFRAME_005fPOINTER_005fREGNUM"></a>Macro: <strong>HARD_FRAME_POINTER_REGNUM</strong></dt>
	<dd><p>On some machines the offset between the frame pointer and starting
	offset of the automatic variables is not known until after register
	allocation has been done (for example, because the saved registers are
	between these two locations). On those machines, define
	<code>FRAME_POINTER_REGNUM</code> the number of a special, fixed register to
	be used internally until the offset is known, and define
	<code>HARD_FRAME_POINTER_REGNUM</code> to be the actual hard register number
	used for the frame pointer.
	</p>
	<p>You should define this macro only in the very rare circumstances when it
	is not possible to calculate the offset between the frame pointer and
	the automatic variables until after register allocation has been
	completed. When this macro is defined, you must also indicate in your
	definition of <code>ELIMINABLE_REGS</code> how to eliminate
	<code>FRAME_POINTER_REGNUM</code> into either <code>HARD_FRAME_POINTER_REGNUM</code>
	or <code>STACK_POINTER_REGNUM</code>.
	</p>
	<p>Do not define this macro if it would be the same as
	<code>FRAME_POINTER_REGNUM</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-ARG_005fPOINTER_005fREGNUM"></a>Macro: <strong>ARG_POINTER_REGNUM</strong></dt>
	<dd><p>The register number of the arg pointer register, which is used to access
	the function’s argument list. On some machines, this is the same as the
	frame pointer register. On some machines, the hardware determines which
	register this is. On other machines, you can choose any register you
	wish for this purpose. If this is not the same register as the frame
	pointer register, then you must mark it as a fixed register according to
	<code>FIXED_REGISTERS</code>, or arrange to be able to eliminate it
	(see <a href="Elimination.html#Elimination">Elimination</a>).
	</p></dd></dl>

	<dl>
	<dt><a name="index-HARD_005fFRAME_005fPOINTER_005fIS_005fFRAME_005fPOINTER"></a>Macro: <strong>HARD_FRAME_POINTER_IS_FRAME_POINTER</strong></dt>
	<dd><p>Define this to a preprocessor constant that is nonzero if
	<code>hard_frame_pointer_rtx</code> and <code>frame_pointer_rtx</code> should be
	the same. The default definition is ‘<samp>(HARD_FRAME_POINTER_REGNUM
	== FRAME_POINTER_REGNUM)</samp>’; you only need to define this macro if that
	definition is not suitable for use in preprocessor conditionals.
	</p></dd></dl>

	<dl>
	<dt><a name="index-HARD_005fFRAME_005fPOINTER_005fIS_005fARG_005fPOINTER"></a>Macro: <strong>HARD_FRAME_POINTER_IS_ARG_POINTER</strong></dt>
	<dd><p>Define this to a preprocessor constant that is nonzero if
	<code>hard_frame_pointer_rtx</code> and <code>arg_pointer_rtx</code> should be the
	same. The default definition is ‘<samp>(HARD_FRAME_POINTER_REGNUM ==
	ARG_POINTER_REGNUM)</samp>’; you only need to define this macro if that
	definition is not suitable for use in preprocessor conditionals.
	</p></dd></dl>

	<dl>
	<dt><a name="index-RETURN_005fADDRESS_005fPOINTER_005fREGNUM"></a>Macro: <strong>RETURN_ADDRESS_POINTER_REGNUM</strong></dt>
	<dd><p>The register number of the return address pointer register, which is used to
	access the current function’s return address from the stack. On some
	machines, the return address is not at a fixed offset from the frame
	pointer or stack pointer or argument pointer. This register can be defined
	to point to the return address on the stack, and then be converted by
	<code>ELIMINABLE_REGS</code> into either the frame pointer or stack pointer.
	</p>
	<p>Do not define this macro unless there is no other way to get the return
	address from the stack.
	</p></dd></dl>

	<dl>
	<dt><a name="index-STATIC_005fCHAIN_005fREGNUM"></a>Macro: <strong>STATIC_CHAIN_REGNUM</strong></dt>
	<dt><a name="index-STATIC_005fCHAIN_005fINCOMING_005fREGNUM"></a>Macro: <strong>STATIC_CHAIN_INCOMING_REGNUM</strong></dt>
	<dd><p>Register numbers used for passing a function’s static chain pointer. If
	register windows are used, the register number as seen by the called
	function is <code>STATIC_CHAIN_INCOMING_REGNUM</code>, while the register
	number as seen by the calling function is <code>STATIC_CHAIN_REGNUM</code>. If
	these registers are the same, <code>STATIC_CHAIN_INCOMING_REGNUM</code> need
	not be defined.
	</p>
	<p>The static chain register need not be a fixed register.
	</p>
	<p>If the static chain is passed in memory, these macros should not be
	defined; instead, the <code>TARGET_STATIC_CHAIN</code> hook should be used.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fSTATIC_005fCHAIN"></a>Target Hook: <em>rtx</em> <strong>TARGET_STATIC_CHAIN</strong> <em>(const_tree <var>fndecl</var>, bool <var>incoming_p</var>)</em></dt>
	<dd><p>This hook replaces the use of <code>STATIC_CHAIN_REGNUM</code> et al for
	targets that may use different static chain locations for different
	nested functions. This may be required if the target has function
	attributes that affect the calling conventions of the function and
	those calling conventions use different static chain locations.
	</p>
	<p>The default version of this hook uses <code>STATIC_CHAIN_REGNUM</code> et al.
	</p>
	<p>If the static chain is passed in memory, this hook should be used to
	provide rtx giving <code>mem</code> expressions that denote where they are stored.
	Often the <code>mem</code> expression as seen by the caller will be at an offset
	from the stack pointer and the <code>mem</code> expression as seen by the callee
	will be at an offset from the frame pointer.
	<a name="index-stack_005fpointer_005frtx"></a>
	<a name="index-frame_005fpointer_005frtx"></a>
	<a name="index-arg_005fpointer_005frtx"></a>
	The variables <code>stack_pointer_rtx</code>, <code>frame_pointer_rtx</code>, and
	<code>arg_pointer_rtx</code> will have been initialized and should be used
	to refer to those items.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DWARF_005fFRAME_005fREGISTERS"></a>Macro: <strong>DWARF_FRAME_REGISTERS</strong></dt>
	<dd><p>This macro specifies the maximum number of hard registers that can be
	saved in a call frame. This is used to size data structures used in
	DWARF2 exception handling.
	</p>
	<p>Prior to GCC 3.0, this macro was needed in order to establish a stable
	exception handling ABI in the face of adding new hard registers for ISA
	extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
	in the number of hard registers. Nevertheless, this macro can still be
	used to reduce the runtime memory requirements of the exception handling
	routines, which can be substantial if the ISA contains a lot of
	registers that are not call-saved.
	</p>
	<p>If this macro is not defined, it defaults to
	<code>FIRST_PSEUDO_REGISTER</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-PRE_005fGCC3_005fDWARF_005fFRAME_005fREGISTERS"></a>Macro: <strong>PRE_GCC3_DWARF_FRAME_REGISTERS</strong></dt>
	<dd>
	<p>This macro is similar to <code>DWARF_FRAME_REGISTERS</code>, but is provided
	for backward compatibility in pre GCC 3.0 compiled code.
	</p>
	<p>If this macro is not defined, it defaults to
	<code>DWARF_FRAME_REGISTERS</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DWARF_005fREG_005fTO_005fUNWIND_005fCOLUMN"></a>Macro: <strong>DWARF_REG_TO_UNWIND_COLUMN</strong> <em>(<var>regno</var>)</em></dt>
	<dd>
	<p>Define this macro if the target’s representation for dwarf registers
	is different than the internal representation for unwind column.
	Given a dwarf register, this macro should return the internal unwind
	column number to use instead.
	</p>
	<p>See the PowerPC’s SPE target for an example.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DWARF_005fFRAME_005fREGNUM"></a>Macro: <strong>DWARF_FRAME_REGNUM</strong> <em>(<var>regno</var>)</em></dt>
	<dd>
	<p>Define this macro if the target’s representation for dwarf registers
	used in .eh_frame or .debug_frame is different from that used in other
	debug info sections. Given a GCC hard register number, this macro
	should return the .eh_frame register number. The default is
	<code>DBX_REGISTER_NUMBER (<var>regno</var>)</code>.
	</p>
	</dd></dl>

	<dl>
	<dt><a name="index-DWARF2_005fFRAME_005fREG_005fOUT"></a>Macro: <strong>DWARF2_FRAME_REG_OUT</strong> <em>(<var>regno</var>, <var>for_eh</var>)</em></dt>
	<dd>
	<p>Define this macro to map register numbers held in the call frame info
	that GCC has collected using <code>DWARF_FRAME_REGNUM</code> to those that
	should be output in .debug_frame (<code><var>for_eh</var></code> is zero) and
	.eh_frame (<code><var>for_eh</var></code> is nonzero). The default is to
	return <code><var>regno</var></code>.
	</p>
	</dd></dl>

	<dl>
	<dt><a name="index-REG_005fVALUE_005fIN_005fUNWIND_005fCONTEXT"></a>Macro: <strong>REG_VALUE_IN_UNWIND_CONTEXT</strong></dt>
	<dd>
	<p>Define this macro if the target stores register values as
	<code>_Unwind_Word</code> type in unwind context. It should be defined if
	target register size is larger than the size of <code>void *</code>. The
	default is to store register values as <code>void *</code> type.
	</p>
	</dd></dl>

	<dl>
	<dt><a name="index-ASSUME_005fEXTENDED_005fUNWIND_005fCONTEXT"></a>Macro: <strong>ASSUME_EXTENDED_UNWIND_CONTEXT</strong></dt>
	<dd>
	<p>Define this macro to be 1 if the target always uses extended unwind
	context with version, args_size and by_value fields. If it is undefined,
	it will be defined to 1 when <code>REG_VALUE_IN_UNWIND_CONTEXT</code> is
	defined and 0 otherwise.
	</p>
	</dd></dl>

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