aarch64-linux-gnu-4.9/share/doc/gccint/Exception-Region-Output.html - toolchains/linux-x86/gcc - Git at Google

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 <a name="Exception-Region-Output"></a>
 <div class="header">
 <p>
 Next: <a href="Alignment-Output.html#Alignment-Output" accesskey="n" rel="next">Alignment Output</a>, Previous: <a href="Dispatch-Tables.html#Dispatch-Tables" accesskey="p" rel="prev">Dispatch Tables</a>, Up: <a href="Assembler-Format.html#Assembler-Format" accesskey="u" rel="up">Assembler Format</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="Assembler-Commands-for-Exception-Regions"></a>
 <h4 class="subsection">17.21.9 Assembler Commands for Exception Regions</h4>


 <p>This describes commands marking the start and the end of an exception
 region.
 </p>
 <dl>
 <dt><a name="index-EH_005fFRAME_005fSECTION_005fNAME"></a>Macro: <strong>EH_FRAME_SECTION_NAME</strong></dt>
 <dd><p>If defined, a C string constant for the name of the section containing
 exception handling frame unwind information.  If not defined, GCC will
 provide a default definition if the target supports named sections.
 <samp>crtstuff.c</samp> uses this macro to switch to the appropriate section.
 </p>
 <p>You should define this symbol if your target supports DWARF 2 frame
 unwind information and the default definition does not work.
 </p></dd></dl>

 <dl>
 <dt><a name="index-EH_005fFRAME_005fIN_005fDATA_005fSECTION"></a>Macro: <strong>EH_FRAME_IN_DATA_SECTION</strong></dt>
 <dd><p>If defined, DWARF 2 frame unwind information will be placed in the
 data section even though the target supports named sections.  This
 might be necessary, for instance, if the system linker does garbage
 collection and sections cannot be marked as not to be collected.
 </p>
 <p>Do not define this macro unless <code>TARGET_ASM_NAMED_SECTION</code> is
 also defined.
 </p></dd></dl>

 <dl>
 <dt><a name="index-EH_005fTABLES_005fCAN_005fBE_005fREAD_005fONLY"></a>Macro: <strong>EH_TABLES_CAN_BE_READ_ONLY</strong></dt>
 <dd><p>Define this macro to 1 if your target is such that no frame unwind
 information encoding used with non-PIC code will ever require a
 runtime relocation, but the linker may not support merging read-only
 and read-write sections into a single read-write section.
 </p></dd></dl>

 <dl>
 <dt><a name="index-MASK_005fRETURN_005fADDR"></a>Macro: <strong>MASK_RETURN_ADDR</strong></dt>
 <dd><p>An rtx used to mask the return address found via <code>RETURN_ADDR_RTX</code>, so
 that it does not contain any extraneous set bits in it.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DWARF2_005fUNWIND_005fINFO"></a>Macro: <strong>DWARF2_UNWIND_INFO</strong></dt>
 <dd><p>Define this macro to 0 if your target supports DWARF 2 frame unwind
 information, but it does not yet work with exception handling.
 Otherwise, if your target supports this information (if it defines
 <code>INCOMING_RETURN_ADDR_RTX</code> and <code>OBJECT_FORMAT_ELF</code>),
 GCC will provide a default definition of 1.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fEXCEPT_005fUNWIND_005fINFO"></a>Common Target Hook: <em>enum unwind_info_type</em> <strong>TARGET_EXCEPT_UNWIND_INFO</strong> <em>(struct gcc_options *<var>opts</var>)</em></dt>
 <dd><p>This hook defines the mechanism that will be used for exception handling
 by the target.  If the target has ABI specified unwind tables, the hook
 should return <code>UI_TARGET</code>.  If the target is to use the
 <code>setjmp</code>/<code>longjmp</code>-based exception handling scheme, the hook
 should return <code>UI_SJLJ</code>.  If the target supports DWARF 2 frame unwind
 information, the hook should return <code>UI_DWARF2</code>.
 </p>
 <p>A target may, if exceptions are disabled, choose to return <code>UI_NONE</code>.
 This may end up simplifying other parts of target-specific code.  The
 default implementation of this hook never returns <code>UI_NONE</code>.
 </p>
 <p>Note that the value returned by this hook should be constant.  It should
 not depend on anything except the command-line switches described by
 <var>opts</var>.  In particular, the
 setting <code>UI_SJLJ</code> must be fixed at compiler start-up as C pre-processor
 macros and builtin functions related to exception handling are set up
 depending on this setting.
 </p>
 <p>The default implementation of the hook first honors the
 <samp>--enable-sjlj-exceptions</samp> configure option, then
 <code>DWARF2_UNWIND_INFO</code>, and finally defaults to <code>UI_SJLJ</code>.  If
 <code>DWARF2_UNWIND_INFO</code> depends on command-line options, the target
 must define this hook so that <var>opts</var> is used correctly.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fUNWIND_005fTABLES_005fDEFAULT"></a>Common Target Hook: <em>bool</em> <strong>TARGET_UNWIND_TABLES_DEFAULT</strong></dt>
 <dd><p>This variable should be set to <code>true</code> if the target ABI requires unwinding
 tables even when exceptions are not used.  It must not be modified by
 command-line option processing.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DONT_005fUSE_005fBUILTIN_005fSETJMP"></a>Macro: <strong>DONT_USE_BUILTIN_SETJMP</strong></dt>
 <dd><p>Define this macro to 1 if the <code>setjmp</code>/<code>longjmp</code>-based scheme
 should use the <code>setjmp</code>/<code>longjmp</code> functions from the C library
 instead of the <code>__builtin_setjmp</code>/<code>__builtin_longjmp</code> machinery.
 </p></dd></dl>

 <dl>
 <dt><a name="index-JMP_005fBUF_005fSIZE"></a>Macro: <strong>JMP_BUF_SIZE</strong></dt>
 <dd><p>This macro has no effect unless <code>DONT_USE_BUILTIN_SETJMP</code> is also
 defined.  Define this macro if the default size of <code>jmp_buf</code> buffer
 for the <code>setjmp</code>/<code>longjmp</code>-based exception handling mechanism
 is not large enough, or if it is much too large.
 The default size is <code>FIRST_PSEUDO_REGISTER * sizeof(void *)</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-DWARF_005fCIE_005fDATA_005fALIGNMENT"></a>Macro: <strong>DWARF_CIE_DATA_ALIGNMENT</strong></dt>
 <dd><p>This macro need only be defined if the target might save registers in the
 function prologue at an offset to the stack pointer that is not aligned to
 <code>UNITS_PER_WORD</code>.  The definition should be the negative minimum
 alignment if <code>STACK_GROWS_DOWNWARD</code> is defined, and the positive
 minimum alignment otherwise.  See <a href="SDB-and-DWARF.html#SDB-and-DWARF">SDB and DWARF</a>.  Only applicable if
 the target supports DWARF 2 frame unwind information.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fTERMINATE_005fDW2_005fEH_005fFRAME_005fINFO"></a>Target Hook: <em>bool</em> <strong>TARGET_TERMINATE_DW2_EH_FRAME_INFO</strong></dt>
 <dd><p>Contains the value true if the target should add a zero word onto the
 end of a Dwarf-2 frame info section when used for exception handling.
 Default value is false if <code>EH_FRAME_SECTION_NAME</code> is defined, and
 true otherwise.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fDWARF_005fREGISTER_005fSPAN"></a>Target Hook: <em>rtx</em> <strong>TARGET_DWARF_REGISTER_SPAN</strong> <em>(rtx <var>reg</var>)</em></dt>
 <dd><p>Given a register, this hook should return a parallel of registers to
 represent where to find the register pieces.  Define this hook if the
 register and its mode are represented in Dwarf in non-contiguous
 locations, or if the register should be represented in more than one
 register in Dwarf.  Otherwise, this hook should return <code>NULL_RTX</code>.
 If not defined, the default is to return <code>NULL_RTX</code>.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fINIT_005fDWARF_005fREG_005fSIZES_005fEXTRA"></a>Target Hook: <em>void</em> <strong>TARGET_INIT_DWARF_REG_SIZES_EXTRA</strong> <em>(tree <var>address</var>)</em></dt>
 <dd><p>If some registers are represented in Dwarf-2 unwind information in
 multiple pieces, define this hook to fill in information about the
 sizes of those pieces in the table used by the unwinder at runtime.
 It will be called by <code>expand_builtin_init_dwarf_reg_sizes</code> after
 filling in a single size corresponding to each hard register;
 <var>address</var> is the address of the table.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fASM_005fTTYPE"></a>Target Hook: <em>bool</em> <strong>TARGET_ASM_TTYPE</strong> <em>(rtx <var>sym</var>)</em></dt>
 <dd><p>This hook is used to output a reference from a frame unwinding table to
 the type_info object identified by <var>sym</var>.  It should return <code>true</code>
 if the reference was output.  Returning <code>false</code> will cause the
 reference to be output using the normal Dwarf2 routines.
 </p></dd></dl>

 <dl>
 <dt><a name="index-TARGET_005fARM_005fEABI_005fUNWINDER"></a>Target Hook: <em>bool</em> <strong>TARGET_ARM_EABI_UNWINDER</strong></dt>
 <dd><p>This flag should be set to <code>true</code> on targets that use an ARM EABI
 based unwinding library, and <code>false</code> on other targets.  This effects
 the format of unwinding tables, and how the unwinder in entered after
 running a cleanup.  The default is <code>false</code>.
 </p></dd></dl>

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 <div class="header">
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 Next: <a href="Alignment-Output.html#Alignment-Output" accesskey="n" rel="next">Alignment Output</a>, Previous: <a href="Dispatch-Tables.html#Dispatch-Tables" accesskey="p" rel="prev">Dispatch Tables</a>, Up: <a href="Assembler-Format.html#Assembler-Format" accesskey="u" rel="up">Assembler Format</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="Exception-Region-Output"></a>
	<div class="header">
	<p>
	Next: <a href="Alignment-Output.html#Alignment-Output" accesskey="n" rel="next">Alignment Output</a>, Previous: <a href="Dispatch-Tables.html#Dispatch-Tables" accesskey="p" rel="prev">Dispatch Tables</a>, Up: <a href="Assembler-Format.html#Assembler-Format" accesskey="u" rel="up">Assembler Format</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="Assembler-Commands-for-Exception-Regions"></a>
	<h4 class="subsection">17.21.9 Assembler Commands for Exception Regions</h4>


	<p>This describes commands marking the start and the end of an exception
	region.
	</p>
	<dl>
	<dt><a name="index-EH_005fFRAME_005fSECTION_005fNAME"></a>Macro: <strong>EH_FRAME_SECTION_NAME</strong></dt>
	<dd><p>If defined, a C string constant for the name of the section containing
	exception handling frame unwind information. If not defined, GCC will
	provide a default definition if the target supports named sections.
	<samp>crtstuff.c</samp> uses this macro to switch to the appropriate section.
	</p>
	<p>You should define this symbol if your target supports DWARF 2 frame
	unwind information and the default definition does not work.
	</p></dd></dl>

	<dl>
	<dt><a name="index-EH_005fFRAME_005fIN_005fDATA_005fSECTION"></a>Macro: <strong>EH_FRAME_IN_DATA_SECTION</strong></dt>
	<dd><p>If defined, DWARF 2 frame unwind information will be placed in the
	data section even though the target supports named sections. This
	might be necessary, for instance, if the system linker does garbage
	collection and sections cannot be marked as not to be collected.
	</p>
	<p>Do not define this macro unless <code>TARGET_ASM_NAMED_SECTION</code> is
	also defined.
	</p></dd></dl>

	<dl>
	<dt><a name="index-EH_005fTABLES_005fCAN_005fBE_005fREAD_005fONLY"></a>Macro: <strong>EH_TABLES_CAN_BE_READ_ONLY</strong></dt>
	<dd><p>Define this macro to 1 if your target is such that no frame unwind
	information encoding used with non-PIC code will ever require a
	runtime relocation, but the linker may not support merging read-only
	and read-write sections into a single read-write section.
	</p></dd></dl>

	<dl>
	<dt><a name="index-MASK_005fRETURN_005fADDR"></a>Macro: <strong>MASK_RETURN_ADDR</strong></dt>
	<dd><p>An rtx used to mask the return address found via <code>RETURN_ADDR_RTX</code>, so
	that it does not contain any extraneous set bits in it.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DWARF2_005fUNWIND_005fINFO"></a>Macro: <strong>DWARF2_UNWIND_INFO</strong></dt>
	<dd><p>Define this macro to 0 if your target supports DWARF 2 frame unwind
	information, but it does not yet work with exception handling.
	Otherwise, if your target supports this information (if it defines
	<code>INCOMING_RETURN_ADDR_RTX</code> and <code>OBJECT_FORMAT_ELF</code>),
	GCC will provide a default definition of 1.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fEXCEPT_005fUNWIND_005fINFO"></a>Common Target Hook: <em>enum unwind_info_type</em> <strong>TARGET_EXCEPT_UNWIND_INFO</strong> <em>(struct gcc_options *<var>opts</var>)</em></dt>
	<dd><p>This hook defines the mechanism that will be used for exception handling
	by the target. If the target has ABI specified unwind tables, the hook
	should return <code>UI_TARGET</code>. If the target is to use the
	<code>setjmp</code>/<code>longjmp</code>-based exception handling scheme, the hook
	should return <code>UI_SJLJ</code>. If the target supports DWARF 2 frame unwind
	information, the hook should return <code>UI_DWARF2</code>.
	</p>
	<p>A target may, if exceptions are disabled, choose to return <code>UI_NONE</code>.
	This may end up simplifying other parts of target-specific code. The
	default implementation of this hook never returns <code>UI_NONE</code>.
	</p>
	<p>Note that the value returned by this hook should be constant. It should
	not depend on anything except the command-line switches described by
	<var>opts</var>. In particular, the
	setting <code>UI_SJLJ</code> must be fixed at compiler start-up as C pre-processor
	macros and builtin functions related to exception handling are set up
	depending on this setting.
	</p>
	<p>The default implementation of the hook first honors the
	<samp>--enable-sjlj-exceptions</samp> configure option, then
	<code>DWARF2_UNWIND_INFO</code>, and finally defaults to <code>UI_SJLJ</code>. If
	<code>DWARF2_UNWIND_INFO</code> depends on command-line options, the target
	must define this hook so that <var>opts</var> is used correctly.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fUNWIND_005fTABLES_005fDEFAULT"></a>Common Target Hook: <em>bool</em> <strong>TARGET_UNWIND_TABLES_DEFAULT</strong></dt>
	<dd><p>This variable should be set to <code>true</code> if the target ABI requires unwinding
	tables even when exceptions are not used. It must not be modified by
	command-line option processing.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DONT_005fUSE_005fBUILTIN_005fSETJMP"></a>Macro: <strong>DONT_USE_BUILTIN_SETJMP</strong></dt>
	<dd><p>Define this macro to 1 if the <code>setjmp</code>/<code>longjmp</code>-based scheme
	should use the <code>setjmp</code>/<code>longjmp</code> functions from the C library
	instead of the <code>__builtin_setjmp</code>/<code>__builtin_longjmp</code> machinery.
	</p></dd></dl>

	<dl>
	<dt><a name="index-JMP_005fBUF_005fSIZE"></a>Macro: <strong>JMP_BUF_SIZE</strong></dt>
	<dd><p>This macro has no effect unless <code>DONT_USE_BUILTIN_SETJMP</code> is also
	defined. Define this macro if the default size of <code>jmp_buf</code> buffer
	for the <code>setjmp</code>/<code>longjmp</code>-based exception handling mechanism
	is not large enough, or if it is much too large.
	The default size is <code>FIRST_PSEUDO_REGISTER * sizeof(void *)</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-DWARF_005fCIE_005fDATA_005fALIGNMENT"></a>Macro: <strong>DWARF_CIE_DATA_ALIGNMENT</strong></dt>
	<dd><p>This macro need only be defined if the target might save registers in the
	function prologue at an offset to the stack pointer that is not aligned to
	<code>UNITS_PER_WORD</code>. The definition should be the negative minimum
	alignment if <code>STACK_GROWS_DOWNWARD</code> is defined, and the positive
	minimum alignment otherwise. See <a href="SDB-and-DWARF.html#SDB-and-DWARF">SDB and DWARF</a>. Only applicable if
	the target supports DWARF 2 frame unwind information.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fTERMINATE_005fDW2_005fEH_005fFRAME_005fINFO"></a>Target Hook: <em>bool</em> <strong>TARGET_TERMINATE_DW2_EH_FRAME_INFO</strong></dt>
	<dd><p>Contains the value true if the target should add a zero word onto the
	end of a Dwarf-2 frame info section when used for exception handling.
	Default value is false if <code>EH_FRAME_SECTION_NAME</code> is defined, and
	true otherwise.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fDWARF_005fREGISTER_005fSPAN"></a>Target Hook: <em>rtx</em> <strong>TARGET_DWARF_REGISTER_SPAN</strong> <em>(rtx <var>reg</var>)</em></dt>
	<dd><p>Given a register, this hook should return a parallel of registers to
	represent where to find the register pieces. Define this hook if the
	register and its mode are represented in Dwarf in non-contiguous
	locations, or if the register should be represented in more than one
	register in Dwarf. Otherwise, this hook should return <code>NULL_RTX</code>.
	If not defined, the default is to return <code>NULL_RTX</code>.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fINIT_005fDWARF_005fREG_005fSIZES_005fEXTRA"></a>Target Hook: <em>void</em> <strong>TARGET_INIT_DWARF_REG_SIZES_EXTRA</strong> <em>(tree <var>address</var>)</em></dt>
	<dd><p>If some registers are represented in Dwarf-2 unwind information in
	multiple pieces, define this hook to fill in information about the
	sizes of those pieces in the table used by the unwinder at runtime.
	It will be called by <code>expand_builtin_init_dwarf_reg_sizes</code> after
	filling in a single size corresponding to each hard register;
	<var>address</var> is the address of the table.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fASM_005fTTYPE"></a>Target Hook: <em>bool</em> <strong>TARGET_ASM_TTYPE</strong> <em>(rtx <var>sym</var>)</em></dt>
	<dd><p>This hook is used to output a reference from a frame unwinding table to
	the type_info object identified by <var>sym</var>. It should return <code>true</code>
	if the reference was output. Returning <code>false</code> will cause the
	reference to be output using the normal Dwarf2 routines.
	</p></dd></dl>

	<dl>
	<dt><a name="index-TARGET_005fARM_005fEABI_005fUNWINDER"></a>Target Hook: <em>bool</em> <strong>TARGET_ARM_EABI_UNWINDER</strong></dt>
	<dd><p>This flag should be set to <code>true</code> on targets that use an ARM EABI
	based unwinding library, and <code>false</code> on other targets. This effects
	the format of unwinding tables, and how the unwinder in entered after
	running a cleanup. The default is <code>false</code>.
	</p></dd></dl>

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