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260 lines
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260 lines
13 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Frame Registers - GNU Compiler Collection (GCC) Internals</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<link rel="up" href="Stack-and-Calling.html#Stack-and-Calling" title="Stack and Calling">
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<link rel="prev" href="Stack-Checking.html#Stack-Checking" title="Stack Checking">
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<link rel="next" href="Elimination.html#Elimination" title="Elimination">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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</head>
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<body>
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<div class="node">
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<a name="Frame-Registers"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Elimination.html#Elimination">Elimination</a>,
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Previous: <a rel="previous" accesskey="p" href="Stack-Checking.html#Stack-Checking">Stack Checking</a>,
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Up: <a rel="up" accesskey="u" href="Stack-and-Calling.html#Stack-and-Calling">Stack and Calling</a>
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<hr>
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</div>
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<h4 class="subsection">17.9.4 Registers That Address the Stack Frame</h4>
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<!-- prevent bad page break with this line -->
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<p>This discusses registers that address the stack frame.
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<div class="defun">
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— Macro: <b>STACK_POINTER_REGNUM</b><var><a name="index-STACK_005fPOINTER_005fREGNUM-4187"></a></var><br>
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<blockquote><p>The register number of the stack pointer register, which must also be a
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fixed register according to <code>FIXED_REGISTERS</code>. On most machines,
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the hardware determines which register this is.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>FRAME_POINTER_REGNUM</b><var><a name="index-FRAME_005fPOINTER_005fREGNUM-4188"></a></var><br>
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<blockquote><p>The register number of the frame pointer register, which is used to
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access automatic variables in the stack frame. On some machines, the
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hardware determines which register this is. On other machines, you can
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choose any register you wish for this purpose.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>HARD_FRAME_POINTER_REGNUM</b><var><a name="index-HARD_005fFRAME_005fPOINTER_005fREGNUM-4189"></a></var><br>
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<blockquote><p>On some machines the offset between the frame pointer and starting
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offset of the automatic variables is not known until after register
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allocation has been done (for example, because the saved registers are
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between these two locations). On those machines, define
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<code>FRAME_POINTER_REGNUM</code> the number of a special, fixed register to
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be used internally until the offset is known, and define
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<code>HARD_FRAME_POINTER_REGNUM</code> to be the actual hard register number
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used for the frame pointer.
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<p>You should define this macro only in the very rare circumstances when it
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is not possible to calculate the offset between the frame pointer and
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the automatic variables until after register allocation has been
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completed. When this macro is defined, you must also indicate in your
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definition of <code>ELIMINABLE_REGS</code> how to eliminate
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<code>FRAME_POINTER_REGNUM</code> into either <code>HARD_FRAME_POINTER_REGNUM</code>
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or <code>STACK_POINTER_REGNUM</code>.
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<p>Do not define this macro if it would be the same as
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<code>FRAME_POINTER_REGNUM</code>.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>ARG_POINTER_REGNUM</b><var><a name="index-ARG_005fPOINTER_005fREGNUM-4190"></a></var><br>
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<blockquote><p>The register number of the arg pointer register, which is used to access
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the function's argument list. On some machines, this is the same as the
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frame pointer register. On some machines, the hardware determines which
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register this is. On other machines, you can choose any register you
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wish for this purpose. If this is not the same register as the frame
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pointer register, then you must mark it as a fixed register according to
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<code>FIXED_REGISTERS</code>, or arrange to be able to eliminate it
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(see <a href="Elimination.html#Elimination">Elimination</a>).
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>HARD_FRAME_POINTER_IS_FRAME_POINTER</b><var><a name="index-HARD_005fFRAME_005fPOINTER_005fIS_005fFRAME_005fPOINTER-4191"></a></var><br>
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<blockquote><p>Define this to a preprocessor constant that is nonzero if
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<code>hard_frame_pointer_rtx</code> and <code>frame_pointer_rtx</code> should be
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the same. The default definition is ‘<samp><span class="samp">(HARD_FRAME_POINTER_REGNUM
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== FRAME_POINTER_REGNUM)</span></samp>’; you only need to define this macro if that
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definition is not suitable for use in preprocessor conditionals.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>HARD_FRAME_POINTER_IS_ARG_POINTER</b><var><a name="index-HARD_005fFRAME_005fPOINTER_005fIS_005fARG_005fPOINTER-4192"></a></var><br>
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<blockquote><p>Define this to a preprocessor constant that is nonzero if
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<code>hard_frame_pointer_rtx</code> and <code>arg_pointer_rtx</code> should be the
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same. The default definition is ‘<samp><span class="samp">(HARD_FRAME_POINTER_REGNUM ==
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ARG_POINTER_REGNUM)</span></samp>’; you only need to define this macro if that
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definition is not suitable for use in preprocessor conditionals.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>RETURN_ADDRESS_POINTER_REGNUM</b><var><a name="index-RETURN_005fADDRESS_005fPOINTER_005fREGNUM-4193"></a></var><br>
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<blockquote><p>The register number of the return address pointer register, which is used to
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access the current function's return address from the stack. On some
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machines, the return address is not at a fixed offset from the frame
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pointer or stack pointer or argument pointer. This register can be defined
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to point to the return address on the stack, and then be converted by
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<code>ELIMINABLE_REGS</code> into either the frame pointer or stack pointer.
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<p>Do not define this macro unless there is no other way to get the return
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address from the stack.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>STATIC_CHAIN_REGNUM</b><var><a name="index-STATIC_005fCHAIN_005fREGNUM-4194"></a></var><br>
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— Macro: <b>STATIC_CHAIN_INCOMING_REGNUM</b><var><a name="index-STATIC_005fCHAIN_005fINCOMING_005fREGNUM-4195"></a></var><br>
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<blockquote><p>Register numbers used for passing a function's static chain pointer. If
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register windows are used, the register number as seen by the called
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function is <code>STATIC_CHAIN_INCOMING_REGNUM</code>, while the register
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number as seen by the calling function is <code>STATIC_CHAIN_REGNUM</code>. If
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these registers are the same, <code>STATIC_CHAIN_INCOMING_REGNUM</code> need
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not be defined.
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<p>The static chain register need not be a fixed register.
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<p>If the static chain is passed in memory, these macros should not be
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defined; instead, the <code>TARGET_STATIC_CHAIN</code> hook should be used.
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</p></blockquote></div>
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<div class="defun">
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— Target Hook: rtx <b>TARGET_STATIC_CHAIN</b> (<var>const_tree fndecl_or_type, bool incoming_p</var>)<var><a name="index-TARGET_005fSTATIC_005fCHAIN-4196"></a></var><br>
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<blockquote><p>This hook replaces the use of <code>STATIC_CHAIN_REGNUM</code> et al for
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targets that may use different static chain locations for different
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nested functions. This may be required if the target has function
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attributes that affect the calling conventions of the function and
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those calling conventions use different static chain locations.
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<p>The default version of this hook uses <code>STATIC_CHAIN_REGNUM</code> et al.
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<p>If the static chain is passed in memory, this hook should be used to
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provide rtx giving <code>mem</code> expressions that denote where they are stored.
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Often the <code>mem</code> expression as seen by the caller will be at an offset
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from the stack pointer and the <code>mem</code> expression as seen by the callee
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will be at an offset from the frame pointer.
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<a name="index-stack_005fpointer_005frtx-4197"></a><a name="index-frame_005fpointer_005frtx-4198"></a><a name="index-arg_005fpointer_005frtx-4199"></a>The variables <code>stack_pointer_rtx</code>, <code>frame_pointer_rtx</code>, and
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<code>arg_pointer_rtx</code> will have been initialized and should be used
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to refer to those items.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>DWARF_FRAME_REGISTERS</b><var><a name="index-DWARF_005fFRAME_005fREGISTERS-4200"></a></var><br>
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<blockquote><p>This macro specifies the maximum number of hard registers that can be
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saved in a call frame. This is used to size data structures used in
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DWARF2 exception handling.
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<p>Prior to GCC 3.0, this macro was needed in order to establish a stable
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exception handling ABI in the face of adding new hard registers for ISA
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extensions. In GCC 3.0 and later, the EH ABI is insulated from changes
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in the number of hard registers. Nevertheless, this macro can still be
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used to reduce the runtime memory requirements of the exception handling
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routines, which can be substantial if the ISA contains a lot of
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registers that are not call-saved.
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<p>If this macro is not defined, it defaults to
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<code>FIRST_PSEUDO_REGISTER</code>.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>PRE_GCC3_DWARF_FRAME_REGISTERS</b><var><a name="index-PRE_005fGCC3_005fDWARF_005fFRAME_005fREGISTERS-4201"></a></var><br>
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<blockquote>
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<p>This macro is similar to <code>DWARF_FRAME_REGISTERS</code>, but is provided
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for backward compatibility in pre GCC 3.0 compiled code.
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<p>If this macro is not defined, it defaults to
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<code>DWARF_FRAME_REGISTERS</code>.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>DWARF_REG_TO_UNWIND_COLUMN</b> (<var>regno</var>)<var><a name="index-DWARF_005fREG_005fTO_005fUNWIND_005fCOLUMN-4202"></a></var><br>
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<blockquote>
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<p>Define this macro if the target's representation for dwarf registers
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is different than the internal representation for unwind column.
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Given a dwarf register, this macro should return the internal unwind
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column number to use instead.
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<p>See the PowerPC's SPE target for an example.
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</p></blockquote></div>
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<div class="defun">
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— Macro: <b>DWARF_FRAME_REGNUM</b> (<var>regno</var>)<var><a name="index-DWARF_005fFRAME_005fREGNUM-4203"></a></var><br>
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<blockquote>
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<p>Define this macro if the target's representation for dwarf registers
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used in .eh_frame or .debug_frame is different from that used in other
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debug info sections. Given a GCC hard register number, this macro
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should return the .eh_frame register number. The default is
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<code>DBX_REGISTER_NUMBER (</code><var>regno</var><code>)</code>.
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</blockquote></div>
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<div class="defun">
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— Macro: <b>DWARF2_FRAME_REG_OUT</b> (<var>regno, for_eh</var>)<var><a name="index-DWARF2_005fFRAME_005fREG_005fOUT-4204"></a></var><br>
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<blockquote>
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<p>Define this macro to map register numbers held in the call frame info
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that GCC has collected using <code>DWARF_FRAME_REGNUM</code> to those that
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should be output in .debug_frame (<var>for_eh</var> is zero) and
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.eh_frame (<var>for_eh</var> is nonzero). The default is to
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return <var>regno</var>.
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</blockquote></div>
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<div class="defun">
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— Macro: <b>REG_VALUE_IN_UNWIND_CONTEXT</b><var><a name="index-REG_005fVALUE_005fIN_005fUNWIND_005fCONTEXT-4205"></a></var><br>
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<blockquote>
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<p>Define this macro if the target stores register values as
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<code>_Unwind_Word</code> type in unwind context. It should be defined if
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target register size is larger than the size of <code>void *</code>. The
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default is to store register values as <code>void *</code> type.
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</blockquote></div>
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<div class="defun">
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— Macro: <b>ASSUME_EXTENDED_UNWIND_CONTEXT</b><var><a name="index-ASSUME_005fEXTENDED_005fUNWIND_005fCONTEXT-4206"></a></var><br>
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<blockquote>
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<p>Define this macro to be 1 if the target always uses extended unwind
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context with version, args_size and by_value fields. If it is undefined,
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it will be defined to 1 when <code>REG_VALUE_IN_UNWIND_CONTEXT</code> is
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defined and 0 otherwise.
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</blockquote></div>
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</body></html>
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