14 dlltool

dlltool is used to create the files needed to create dynamiclink libraries (DLLs) on systems which understand PE format imagefiles such as Windows. A DLL contains an export table which containsinformation that the runtime loader needs to resolve references from areferencing program.

The export table is generated by this program by reading in a.def file or scanning the .a and .o files whichwill be in the DLL. A .o file can contain information inspecial .drectve sections with export information.

Note: dlltool is not always built as part of thebinary utilities, since it is only useful for those targets whichsupport 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] [--add-stdcall-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 commandline. It then processes these inputs and if the -e option hasbeen specified it creates a exports file. If the -l optionhas been specified it creates a library file and if the -z optionhas been specified it creates a def file. Any or all of the -e,-l and -z options can be present in one invocation ofdlltool.

When creating a DLL, along with the source for the DLL, it is necessaryto have three other files. dlltool can help with the creation ofthese files.

The first file is a .def file which specifies which functions areexported from the DLL, which functions the DLL imports, and so on. Thisis a text file and can be created by hand, or dlltool can be usedto create it using the -z option. In this case dlltoolwill scan the object files specified on its command line looking forthose functions which have been specially marked as being exported andput entries for them in the .def file it creates.

In order to mark a function as being exported from a DLL, it needs tohave an -export:<name_of_function> entry in the .drectvesection of the object file. This can be done in C by using theasm() 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 fileis linked with the object files that make up the body of the DLL and ithandles the interface between the DLL and the outside world. This is abinary file and it can be created by giving the -e option todlltool when it is creating or reading in a .def file.

The third file needed for DLL creation is the library file that programswill link with in order to access the functions in the DLL. This filecan be created by giving the -l option to dlltool when itis creating or reading in a .def file.

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

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

       gcc -c dll.cdlltool -e exports.o -l dll.lib dll.ogcc dll.o exports.o -o dll.dllgcc 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. Thecontents of this file will be added to the relocation section in theexports 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 objectfiles as symbols to be exported. There is a small list of symbols whichare not exported by default; see the --no-default-excludesoption. 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 defaultbehaviour. The .drectve sections are created by dllexportattributes in the source code.

--exclude-symbols list

Do not export the symbols in list. This is a list of symbol namesseparated by comma or colon characters. The symbol names should notcontain 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 avoidexporting certain special symbols. The current list of symbols to avoidexporting is DllMain@12, DllEntryPoint@0,impure_ptr. You may use the --no-default-excludes optionto go ahead and export these special symbols. This is only meaningfulwhen --export-all-symbols is used.

-S path

--as path

Specifies the path, including the filename, of the assembler to be usedto create the exports file.

-f options

--as-flags options

Specifies any specific command line options to be passed to theassembler when building the exports file. This option will work even ifthe -S option is not used. This option only takes one argument,and if it occurs more than once on the command line, then lateroccurrences will override earlier occurrences. So if it is necessary topass multiple options to the assembler they should be enclosed indouble quotes.

-D name

--dll-name name

Specifies the name to be stored in the .def file as the name ofthe DLL when the -e option is used. If this option is notpresent, then the filename given to the -e option will beused as the name of the DLL.

-m machine

-machine machine

Specifies the type of machine for which the library file should bebuilt. dlltool has a built in default type, depending upon howit was created, but this option can be used to override that. This isnormally only useful when creating DLLs for an ARM processor, when thecontents of the DLL are actually encode using Thumb instructions.

-a

--add-indirect

Specifies that when dlltool is creating the exports file itshould add a section which allows the exported functions to bereferenced without using the import library. Whatever the hell thatmeans!

-U

--add-underscore

Specifies that when dlltool is creating the exports file itshould prepend an underscore to the names of all exported symbols.

--add-stdcall-underscore

Specifies that when dlltool is creating the exports file itshould prepend an underscore to the names of exported stdcallfunctions. Variable names and non-stdcall function names are not modified. This option is useful when creating GNU-compatible import libs for thirdparty DLLs that were built with MS-Windows tools.

-k

--kill-at

Specifies that when dlltool is creating the exports file itshould not append the string @ <number>. These numbers arecalled ordinal numbers and they represent another way of accessing thefunction in a DLL, other than by name.

-A

--add-stdcall-alias

Specifies that when dlltool is creating the exports file itshould 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 DLLimports with the specified prefix. The aliases are created for bothexternal and import symbols with no leading underscore.

-x

--no-idata4

Specifies that when dlltool is creating the exports and libraryfiles it should omit the .idata4 section. This is for compatibilitywith certain operating systems.

-c

--no-idata5

Specifies that when dlltool is creating the exports and libraryfiles it should omit the .idata5 section. This is for compatibilitywith certain operating systems.

-i

--interwork

Specifies that dlltool should mark the objects in the libraryfile and exports file that it produces as supporting interworkingbetween ARM and Thumb code.

-n

--nodelete

Makes dlltool preserve the temporary assembler files it used tocreate the exports file. If this option is repeated then dlltool willalso preserve the temporary object files it uses to create the libraryfile.

-t prefix

--temp-prefix prefix

Makes dlltool use prefix when constructing the names oftemporary assembler and object files. By default, the temp file prefixis 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.

• def file format: The format of the dlltool .def file

Reference Home

Corrections, suggestions, and new documentation should be posted to the Forum.

The text of the Arduino reference is licensed under a Creative Commons Attribution-ShareAlike 3.0 License. Code samples in the reference are released into the public domain.