ld.info: Output Section Keywords
Go forward to Output Section Discarding
Go backward to Output Section Data
Go up to SECTIONS
Go to the top op ld
Output section keywords
There are a couple of keywords which can appear as output section
commands.
`CREATE_OBJECT_SYMBOLS'
The command tells the linker to create a symbol for each input
file. The name of each symbol will be the name of the
corresponding input file. The section of each symbol will be the
output section in which the `CREATE_OBJECT_SYMBOLS' command
appears.
This is conventional for the a.out object file format. It is not
normally used for any other object file format.
`CONSTRUCTORS'
When linking using the a.out object file format, the linker uses an
unusual set construct to support C++ global constructors and
destructors. When linking object file formats which do not support
arbitrary sections, such as ECOFF and XCOFF, the linker will
automatically recognize C++ global constructors and destructors by
name. For these object file formats, the `CONSTRUCTORS' command
tells the linker to place constructor information in the output
section where the `CONSTRUCTORS' command appears. The
`CONSTRUCTORS' command is ignored for other object file formats.
The symbol `__CTOR_LIST__' marks the start of the global
constructors, and the symbol `__DTOR_LIST' marks the end. The
first word in the list is the number of entries, followed by the
address of each constructor or destructor, followed by a zero
word. The compiler must arrange to actually run the code. For
these object file formats GNU C++ normally calls constructors from
a subroutine `__main'; a call to `__main' is automatically
inserted into the startup code for `main'. GNU C++ normally runs
destructors either by using `atexit', or directly from the function
`exit'.
For object file formats such as `COFF' or `ELF' which support
arbitrary section names, GNU C++ will normally arrange to put the
addresses of global constructors and destructors into the `.ctors'
and `.dtors' sections. Placing the following sequence into your
linker script will build the sort of table which the GNU C++
runtime code expects to see.
__CTOR_LIST__ = .;
LONG((__CTOR_END__ - __CTOR_LIST__) / 4 - 2)
*(.ctors)
LONG(0)
__CTOR_END__ = .;
__DTOR_LIST__ = .;
LONG((__DTOR_END__ - __DTOR_LIST__) / 4 - 2)
*(.dtors)
LONG(0)
__DTOR_END__ = .;
If you are using the GNU C++ support for initialization priority,
which provides some control over the order in which global
constructors are run, you must sort the constructors at link time
to ensure that they are executed in the correct order. When using
the `CONSTRUCTORS' command, use `SORT(CONSTRUCTORS)' instead.
When using the `.ctors' and `.dtors' sections, use
`*(SORT(.ctors))' and `*(SORT(.dtors))' instead of just
`*(.ctors)' and `*(.dtors)'.
Normally the compiler and linker will handle these issues
automatically, and you will not need to concern yourself with
them. However, you may need to consider this if you are using C++
and writing your own linker scripts.
Created Wed Sep 1 16:42:37 2004 on bee with info_to_html version 0.9.6.