* ld.texinfo: Clarify the CONSTRUCTORS command.
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Wed May 29 13:13:35 1996 Ian Lance Taylor <ian@cygnus.com>
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* ld.texinfo: Clarify the CONSTRUCTORS command.
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Thu May 23 16:07:44 1996 Ian Lance Taylor <ian@cygnus.com>
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* emultempl/aix.em (gld${EMULATION_NAME}_read_file): Initialize
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@ -340,6 +340,17 @@ the @code{GNUTARGET} environment variable) are more flexible, but
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written to call the old linker.
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@end ifclear
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@kindex --force-exe-suffix
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@item --force-exe-suffix
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Make sure that an output file has a .exe suffix.
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If a successfully built fully linked output file does not have a
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@code{.exe} or @code{.dll} suffix, this option forces the linker to copy
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the output file to one of the same name with a @code{.exe} suffix. This
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option is useful when using unmodified Unix makefiles on a Microsoft
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Windows host, since some versions of Windows won't run an image unless
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it ends in a @code{.exe} suffix.
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@kindex -g
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@item -g
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Ignored. Provided for compatibility with other tools.
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@ -2481,18 +2492,49 @@ command-line options.
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@cindex C++ constructors, arranging in link
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@cindex constructors, arranging in link
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@item CONSTRUCTORS
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This command ties up C++ style constructor and destructor records. The
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details of the constructor representation vary from one object format to
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another, but usually lists of constructors and destructors appear as
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special sections. The @code{CONSTRUCTORS} command specifies where the
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linker is to place the data from these sections, relative to the rest of
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the linked output. Constructor data is marked by the symbol
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@w{@code{__CTOR_LIST__}} at the start, and @w{@code{__CTOR_LIST_END}} at
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the end; destructor data is bracketed similarly, between
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@w{@code{__DTOR_LIST__}} and @w{@code{__DTOR_LIST_END}}. (The compiler
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must arrange to actually run this code; @sc{gnu} C++ calls constructors from
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a subroutine @code{__main}, which it inserts automatically into the
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startup code for @code{main}, and destructors from @code{_exit}.)
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When linking using the @code{a.out} object file format, the linker uses
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an unusual set construct to support C++ global constructors and
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destructors. When linking object file formats which do not support
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arbitrary sections, such as @code{ECOFF} and @code{XCOFF}, the linker
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will automatically recognize C++ global constructors and destructors by
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name. For these object file formats, the @code{CONSTRUCTORS} command
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tells the linker where this information should be placed. The
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@code{CONSTRUCTORS} command is ignored for other object file formats.
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The symbol @w{@code{__CTOR_LIST__}} marks the start of the global
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constructors, and the symbol @w{@code{__DTOR_LIST}} marks the end. The
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first word in the list is the number of entries, followed by the address
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of each constructor or destructor, followed by a zero word. The
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compiler must arrange to actually run the code. For these object file
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formats @sc{gnu} C++ calls constructors from a subroutine @code{__main};
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a call to @code{__main} is automatically inserted into the startup code
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for @code{main}. @sc{gnu} C++ runs destructors either by using
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@code{atexit}, or directly from the function @code{exit}.
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For object file formats such as @code{COFF} or @code{ELF} which support
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multiple sections, @sc{gnu} C++ will normally arrange to put the
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addresses of global constructors and destructors into the @code{.ctors}
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and @code{.dtors} sections. Placing the following sequence into your
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linker script will build the sort of table which the @sc{gnu} C++
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runtime code expects to see.
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@smallexample
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__CTOR_LIST__ = .;
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LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
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*(.ctors)
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LONG(0)
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__CTOR_END__ = .;
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__DTOR_LIST__ = .;
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LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
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*(.dtors)
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LONG(0)
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__DTOR_END__ = .;
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@end smallexample
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Normally the compiler and linker will handle these issues automatically,
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and you will not need to concern yourself with them. However, you may
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need to consider this if you are using C++ and writing your own linker
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scripts.
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@need 1000
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@kindex FLOAT
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