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<h4 class="subsection">17.20.6 Macros Controlling Initialization Routines</h4>
<p>Here are the macros that control how the compiler handles initialization
and termination functions:
<div class="defun">
— Macro: <b>INIT_SECTION_ASM_OP</b><var><a name="index-INIT_005fSECTION_005fASM_005fOP-4670"></a></var><br>
<blockquote><p>If defined, a C string constant, including spacing, for the assembler
operation to identify the following data as initialization code. If not
defined, GCC will assume such a section does not exist. When you are
using special sections for initialization and termination functions, this
macro also controls how <samp><span class="file">crtstuff.c</span></samp> and <samp><span class="file">libgcc2.c</span></samp> arrange to
run the initialization functions.
</p></blockquote></div>
<div class="defun">
— Macro: <b>HAS_INIT_SECTION</b><var><a name="index-HAS_005fINIT_005fSECTION-4671"></a></var><br>
<blockquote><p>If defined, <code>main</code> will not call <code>__main</code> as described above.
This macro should be defined for systems that control start-up code
on a symbol-by-symbol basis, such as OSF/1, and should not
be defined explicitly for systems that support <code>INIT_SECTION_ASM_OP</code>.
</p></blockquote></div>
<div class="defun">
— Macro: <b>LD_INIT_SWITCH</b><var><a name="index-LD_005fINIT_005fSWITCH-4672"></a></var><br>
<blockquote><p>If defined, a C string constant for a switch that tells the linker that
the following symbol is an initialization routine.
</p></blockquote></div>
<div class="defun">
— Macro: <b>LD_FINI_SWITCH</b><var><a name="index-LD_005fFINI_005fSWITCH-4673"></a></var><br>
<blockquote><p>If defined, a C string constant for a switch that tells the linker that
the following symbol is a finalization routine.
</p></blockquote></div>
<div class="defun">
— Macro: <b>COLLECT_SHARED_INIT_FUNC</b> (<var>stream, func</var>)<var><a name="index-COLLECT_005fSHARED_005fINIT_005fFUNC-4674"></a></var><br>
<blockquote><p>If defined, a C statement that will write a function that can be
automatically called when a shared library is loaded. The function
should call <var>func</var>, which takes no arguments. If not defined, and
the object format requires an explicit initialization function, then a
function called <code>_GLOBAL__DI</code> will be generated.
<p>This function and the following one are used by collect2 when linking a
shared library that needs constructors or destructors, or has DWARF2
exception tables embedded in the code.
</p></blockquote></div>
<div class="defun">
— Macro: <b>COLLECT_SHARED_FINI_FUNC</b> (<var>stream, func</var>)<var><a name="index-COLLECT_005fSHARED_005fFINI_005fFUNC-4675"></a></var><br>
<blockquote><p>If defined, a C statement that will write a function that can be
automatically called when a shared library is unloaded. The function
should call <var>func</var>, which takes no arguments. If not defined, and
the object format requires an explicit finalization function, then a
function called <code>_GLOBAL__DD</code> will be generated.
</p></blockquote></div>
<div class="defun">
— Macro: <b>INVOKE__main</b><var><a name="index-INVOKE_005f_005fmain-4676"></a></var><br>
<blockquote><p>If defined, <code>main</code> will call <code>__main</code> despite the presence of
<code>INIT_SECTION_ASM_OP</code>. This macro should be defined for systems
where the init section is not actually run automatically, but is still
useful for collecting the lists of constructors and destructors.
</p></blockquote></div>
<div class="defun">
— Macro: <b>SUPPORTS_INIT_PRIORITY</b><var><a name="index-SUPPORTS_005fINIT_005fPRIORITY-4677"></a></var><br>
<blockquote><p>If nonzero, the C++ <code>init_priority</code> attribute is supported and the
compiler should emit instructions to control the order of initialization
of objects. If zero, the compiler will issue an error message upon
encountering an <code>init_priority</code> attribute.
</p></blockquote></div>
<div class="defun">
— Target Hook: bool <b>TARGET_HAVE_CTORS_DTORS</b><var><a name="index-TARGET_005fHAVE_005fCTORS_005fDTORS-4678"></a></var><br>
<blockquote><p>This value is true if the target supports some “native” method of
collecting constructors and destructors to be run at startup and exit.
It is false if we must use <samp><span class="command">collect2</span></samp>.
</p></blockquote></div>
<div class="defun">
— Target Hook: void <b>TARGET_ASM_CONSTRUCTOR</b> (<var>rtx symbol, int priority</var>)<var><a name="index-TARGET_005fASM_005fCONSTRUCTOR-4679"></a></var><br>
<blockquote><p>If defined, a function that outputs assembler code to arrange to call
the function referenced by <var>symbol</var> at initialization time.
<p>Assume that <var>symbol</var> is a <code>SYMBOL_REF</code> for a function taking
no arguments and with no return value. If the target supports initialization
priorities, <var>priority</var> is a value between 0 and <code>MAX_INIT_PRIORITY</code>;
otherwise it must be <code>DEFAULT_INIT_PRIORITY</code>.
<p>If this macro is not defined by the target, a suitable default will
be chosen if (1) the target supports arbitrary section names, (2) the
target defines <code>CTORS_SECTION_ASM_OP</code>, or (3) <code>USE_COLLECT2</code>
is not defined.
</p></blockquote></div>
<div class="defun">
— Target Hook: void <b>TARGET_ASM_DESTRUCTOR</b> (<var>rtx symbol, int priority</var>)<var><a name="index-TARGET_005fASM_005fDESTRUCTOR-4680"></a></var><br>
<blockquote><p>This is like <code>TARGET_ASM_CONSTRUCTOR</code> but used for termination
functions rather than initialization functions.
</p></blockquote></div>
<p>If <code>TARGET_HAVE_CTORS_DTORS</code> is true, the initialization routine
generated for the generated object file will have static linkage.
<p>If your system uses <samp><span class="command">collect2</span></samp> as the means of processing
constructors, then that program normally uses <samp><span class="command">nm</span></samp> to scan
an object file for constructor functions to be called.
<p>On certain kinds of systems, you can define this macro to make
<samp><span class="command">collect2</span></samp> work faster (and, in some cases, make it work at all):
<div class="defun">
— Macro: <b>OBJECT_FORMAT_COFF</b><var><a name="index-OBJECT_005fFORMAT_005fCOFF-4681"></a></var><br>
<blockquote><p>Define this macro if the system uses COFF (Common Object File Format)
object files, so that <samp><span class="command">collect2</span></samp> can assume this format and scan
object files directly for dynamic constructor/destructor functions.
<p>This macro is effective only in a native compiler; <samp><span class="command">collect2</span></samp> as
part of a cross compiler always uses <samp><span class="command">nm</span></samp> for the target machine.
</p></blockquote></div>
<div class="defun">
— Macro: <b>REAL_NM_FILE_NAME</b><var><a name="index-REAL_005fNM_005fFILE_005fNAME-4682"></a></var><br>
<blockquote><p>Define this macro as a C string constant containing the file name to use
to execute <samp><span class="command">nm</span></samp>. The default is to search the path normally for
<samp><span class="command">nm</span></samp>.
</p></blockquote></div>
<div class="defun">
— Macro: <b>NM_FLAGS</b><var><a name="index-NM_005fFLAGS-4683"></a></var><br>
<blockquote><p><samp><span class="command">collect2</span></samp> calls <samp><span class="command">nm</span></samp> to scan object files for static
constructors and destructors and LTO info. By default, <samp><span class="option">-n</span></samp> is
passed. Define <code>NM_FLAGS</code> to a C string constant if other options
are needed to get the same output format as GNU <samp><span class="command">nm -n</span></samp>
produces.
</p></blockquote></div>
<p>If your system supports shared libraries and has a program to list the
dynamic dependencies of a given library or executable, you can define
these macros to enable support for running initialization and
termination functions in shared libraries:
<div class="defun">
— Macro: <b>LDD_SUFFIX</b><var><a name="index-LDD_005fSUFFIX-4684"></a></var><br>
<blockquote><p>Define this macro to a C string constant containing the name of the program
which lists dynamic dependencies, like <samp><span class="command">ldd</span></samp> under SunOS 4.
</p></blockquote></div>
<div class="defun">
— Macro: <b>PARSE_LDD_OUTPUT</b> (<var>ptr</var>)<var><a name="index-PARSE_005fLDD_005fOUTPUT-4685"></a></var><br>
<blockquote><p>Define this macro to be C code that extracts filenames from the output
of the program denoted by <code>LDD_SUFFIX</code>. <var>ptr</var> is a variable
of type <code>char *</code> that points to the beginning of a line of output
from <code>LDD_SUFFIX</code>. If the line lists a dynamic dependency, the
code must advance <var>ptr</var> to the beginning of the filename on that
line. Otherwise, it must set <var>ptr</var> to <code>NULL</code>.
</p></blockquote></div>
<div class="defun">
— Macro: <b>SHLIB_SUFFIX</b><var><a name="index-SHLIB_005fSUFFIX-4686"></a></var><br>
<blockquote><p>Define this macro to a C string constant containing the default shared
library extension of the target (e.g., ‘<samp><span class="samp">".so"</span></samp>’). <samp><span class="command">collect2</span></samp>
strips version information after this suffix when generating global
constructor and destructor names. This define is only needed on targets
that use <samp><span class="command">collect2</span></samp> to process constructors and destructors.
</p></blockquote></div>
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