File: binutils.info,  Node: dlltool,  Next: Selecting The Target System,  Prev: windres,  Up: Top

13 Create files needed to build and use DLLs
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`dlltool' may be used to create the files needed to build and use
dynamic link libraries (DLLs).

     _Warning:_ `dlltool' is not always built as part of the binary
     utilities, since it is only useful for those targets which support
     DLLs.

     dlltool [`-d'|`--input-def' DEF-FILE-NAME]
             [`-b'|`--base-file' BASE-FILE-NAME]
             [`-e'|`--output-exp' EXPORTS-FILE-NAME]
             [`-z'|`--output-def' DEF-FILE-NAME]
             [`-l'|`--output-lib' LIBRARY-FILE-NAME]
             [`--export-all-symbols'] [`--no-export-all-symbols']
             [`--exclude-symbols' LIST]
             [`--no-default-excludes']
             [`-S'|`--as' PATH-TO-ASSEMBLER] [`-f'|`--as-flags' OPTIONS]
             [`-D'|`--dllname' NAME] [`-m'|`--machine' MACHINE]
             [`-a'|`--add-indirect'] [`-U'|`--add-underscore'] [`-k'|`--kill-at']
             [`-A'|`--add-stdcall-alias']
             [`-p'|`--ext-prefix-alias' PREFIX]
             [`-x'|`--no-idata4'] [`-c'|`--no-idata5'] [`-i'|`--interwork']
             [`-n'|`--nodelete'] [`-t'|`--temp-prefix' PREFIX]
             [`-v'|`--verbose']
             [`-h'|`--help'] [`-V'|`--version']
             [object-file ...]

   `dlltool' reads its inputs, which can come from the `-d' and `-b'
options as well as object files specified on the command line.  It then
processes these inputs and if the `-e' option has been specified it
creates a exports file.  If the `-l' option has been specified it
creates a library file and if the `-z' option has been specified it
creates a def file.  Any or all of the `-e', `-l' and `-z' options can
be present in one invocation of dlltool.

   When creating a DLL, along with the source for the DLL, it is
necessary to have three other files.  `dlltool' can help with the
creation of these files.

   The first file is a `.def' file which specifies which functions are
exported from the DLL, which functions the DLL imports, and so on.  This
is a text file and can be created by hand, or `dlltool' can be used to
create it using the `-z' option.  In this case `dlltool' will scan the
object files specified on its command line looking for those functions
which have been specially marked as being exported and put entries for
them in the .def file it creates.

   In order to mark a function as being exported from a DLL, it needs to
have an `-export:<name_of_function>' entry in the `.drectve' section of
the object file.  This can be done in C by using the asm() operator:

       asm (".section .drectve");
       asm (".ascii \"-export:my_func\"");

       int my_func (void) { ... }

   The second file needed for DLL creation is an exports file.  This
file is linked with the object files that make up the body of the DLL
and it handles the interface between the DLL and the outside world.
This is a binary file and it can be created by giving the `-e' option to
`dlltool' when it is creating or reading in a .def file.

   The third file needed for DLL creation is the library file that
programs will link with in order to access the functions in the DLL.
This file can be created by giving the `-l' option to dlltool when it
is creating or reading in a .def file.

   `dlltool' builds the library file by hand, but it builds the exports
file by creating temporary files containing assembler statements and
then assembling these.  The `-S' command line option can be used to
specify the path to the assembler that dlltool will use, and the `-f'
option can be used to pass specific flags to that assembler.  The `-n'
can be used to prevent dlltool from deleting these temporary assembler
files when it is done, and if `-n' is specified twice then this will
prevent dlltool from deleting the temporary object files it used to
build the library.

   Here is an example of creating a DLL from a source file `dll.c' and
also creating a program (from an object file called `program.o') that
uses that DLL:

       gcc -c dll.c
       dlltool -e exports.o -l dll.lib dll.o
       gcc dll.o exports.o -o dll.dll
       gcc program.o dll.lib -o program

   The command line options have the following meanings:

`-d FILENAME'
`--input-def FILENAME'
     Specifies the name of a .def file to be read in and processed.

`-b FILENAME'
`--base-file FILENAME'
     Specifies the name of a base file to be read in and processed.  The
     contents of this file will be added to the relocation section in
     the exports file generated by dlltool.

`-e FILENAME'
`--output-exp FILENAME'
     Specifies the name of the export file to be created by dlltool.

`-z FILENAME'
`--output-def FILENAME'
     Specifies the name of the .def file to be created by dlltool.

`-l FILENAME'
`--output-lib FILENAME'
     Specifies the name of the library file to be created by dlltool.

`--export-all-symbols'
     Treat all global and weak defined symbols found in the input object
     files as symbols to be exported.  There is a small list of symbols
     which are not exported by default; see the `--no-default-excludes'
     option.  You may add to the list of symbols to not export by using
     the `--exclude-symbols' option.

`--no-export-all-symbols'
     Only export symbols explicitly listed in an input .def file or in
     `.drectve' sections in the input object files.  This is the default
     behaviour.  The `.drectve' sections are created by `dllexport'
     attributes in the source code.

`--exclude-symbols LIST'
     Do not export the symbols in LIST.  This is a list of symbol names
     separated by comma or colon characters.  The symbol names should
     not contain a leading underscore.  This is only meaningful when
     `--export-all-symbols' is used.

`--no-default-excludes'
     When `--export-all-symbols' is used, it will by default avoid
     exporting certain special symbols.  The current list of symbols to
     avoid exporting is `DllMain@12', `DllEntryPoint@0', `impure_ptr'.
     You may use the `--no-default-excludes' option to go ahead and
     export these special symbols.  This is only meaningful when
     `--export-all-symbols' is used.

`-S PATH'
`--as PATH'
     Specifies the path, including the filename, of the assembler to be
     used to create the exports file.

`-f OPTIONS'
`--as-flags OPTIONS'
     Specifies any specific command line options to be passed to the
     assembler when building the exports file.  This option will work
     even if the `-S' option is not used.  This option only takes one
     argument, and if it occurs more than once on the command line,
     then later occurrences will override earlier occurrences.  So if
     it is necessary to pass multiple options to the assembler they
     should be enclosed in double quotes.

`-D NAME'
`--dll-name NAME'
     Specifies the name to be stored in the .def file as the name of
     the DLL when the `-e' option is used.  If this option is not
     present, then the filename given to the `-e' option will be used
     as the name of the DLL.

`-m MACHINE'
`-machine MACHINE'
     Specifies the type of machine for which the library file should be
     built.  `dlltool' has a built in default type, depending upon how
     it was created, but this option can be used to override that.
     This is normally only useful when creating DLLs for an ARM
     processor, when the contents of the DLL are actually encode using
     Thumb instructions.

`-a'
`--add-indirect'
     Specifies that when `dlltool' is creating the exports file it
     should add a section which allows the exported functions to be
     referenced without using the import library.  Whatever the hell
     that means!

`-U'
`--add-underscore'
     Specifies that when `dlltool' is creating the exports file it
     should prepend an underscore to the names of the exported
     functions.  The option is ignored for symbols with an explicit
     internal name specification provided in a .def file.

`-k'
`--kill-at'
     Specifies that when `dlltool' is creating the exports file it
     should not append the string `@ <number>'  The option is ignored
     for symbols with an explicit internal name specification provided
     in a .def file.

`-A'
`--add-stdcall-alias'
     Specifies that when `dlltool' is creating the exports file it
     should add aliases for stdcall symbols without `@ <number>' in
     addition to the symbols with `@ <number>'.

`-p'
`--ext-prefix-alias PREFIX'
     Causes `dlltool' to create external aliases for all DLL imports
     with the specified prefix.  The aliases are created for both
     external and import symbols with no leading underscore.

`-x'
`--no-idata4'
     Specifies that when `dlltool' is creating the exports and library
     files it should omit the `.idata4' section.  This is for
     compatibility with certain operating systems.

`-c'
`--no-idata5'
     Specifies that when `dlltool' is creating the exports and library
     files it should omit the `.idata5' section.  This is for
     compatibility with certain operating systems.

`-i'
`--interwork'
     Specifies that `dlltool' should mark the objects in the library
     file and exports file that it produces as supporting interworking
     between ARM and Thumb code.

`-n'
`--nodelete'
     Makes `dlltool' preserve the temporary assembler files it used to
     create the exports file.  If this option is repeated then dlltool
     will also preserve the temporary object files it uses to create
     the library file.

`-t PREFIX'
`--temp-prefix PREFIX'
     Makes `dlltool' use PREFIX when constructing the names of
     temporary assembler and object files.  By default, the temp file
     prefix is generated from the pid.

`-v'
`--verbose'
     Make dlltool describe what it is doing.

`-h'
`--help'
     Displays a list of command line options and then exits.

`-V'
`--version'
     Displays dlltool's version number and then exits.