GNAT User’s Guide for Native Platforms: Using gnatdll

9.3.5.19 Using gnatdll

gnatdll is a tool to automate the DLL build process once all the Ada and non-Ada sources that make up your DLL have been compiled. gnatdll is actually in charge of two distinct tasks: build the static import library for the DLL and the actual DLL. The form of the gnatdll command is

$ gnatdll [`switches`] `list-of-files` [-largs `opts`]

where list-of-files is a list of ALI and object files. The object file list must be the exact list of objects corresponding to the non-Ada sources whose services are to be included in the DLL. The ALI file list must be the exact list of ALI files for the corresponding Ada sources whose services are to be included in the DLL. If list-of-files is missing, only the static import library is generated.

You may specify any of the following switches to gnatdll:

-a[`address']: Build a non-relocatable DLL at address. If address is not specified the default address 0x11000000 will be used. By default, when this switch is missing, gnatdll builds relocatable DLL. We advise the reader to build relocatable DLL.
-b `address': Set the relocatable DLL base address. By default the address is 0x11000000.
-bargs `opts': Binder options. Pass opts to the binder.
-d `dllfile': dllfile is the name of the DLL. This switch must be present for gnatdll to do anything. The name of the generated import library is obtained algorithmically from dllfile as shown in the following example: if dllfile is xyz.dll, the import library name is libxyz.dll.a. The name of the definition file to use (if not specified by option `-e') is obtained algorithmically from dllfile as shown in the following example: if dllfile is xyz.dll, the definition file used is xyz.def.
-e `deffile': deffile is the name of the definition file.
-g: Generate debugging information. This information is stored in the object file and copied from there to the final DLL file by the linker, where it can be read by the debugger. You must use the `-g' switch if you plan on using the debugger or the symbolic stack traceback.
-h: Help mode. Displays gnatdll switch usage information.
-I`dir': Direct gnatdll to search the dir directory for source and object files needed to build the DLL. (Search Paths and the Run-Time Library (RTL)).
-k: Removes the @`nn' suffix from the import library’s exported names, but keeps them for the link names. You must specify this option if you want to use a Stdcall function in a DLL for which the @`nn' suffix has been removed. This is the case for most of the Windows NT DLL for example. This option has no effect when `-n' option is specified.
-l `file': The list of ALI and object files used to build the DLL are listed in file, instead of being given in the command line. Each line in file contains the name of an ALI or object file.
-n: No Import. Do not create the import library.
-q: Quiet mode. Do not display unnecessary messages.
-v: Verbose mode. Display extra information.
-largs `opts': Linker options. Pass opts to the linker.

gnatdll Example

As an example the command to build a relocatable DLL from api.adb once api.adb has been compiled and api.def created is

$ gnatdll -d api.dll api.ali

The above command creates two files: libapi.dll.a (the import library) and api.dll (the actual DLL). If you want to create only the DLL, just type:

$ gnatdll -d api.dll -n api.ali

Alternatively if you want to create just the import library, type:

$ gnatdll -d api.dll

gnatdll behind the Scenes

This section details the steps involved in creating a DLL. gnatdll does these steps for you. Unless you are interested in understanding what goes on behind the scenes, you should skip this section.

We use the previous example of a DLL containing the Ada package API, to illustrate the steps necessary to build a DLL. The starting point is a set of objects that will make up the DLL and the corresponding ALI files. In the case of this example this means that api.o and api.ali are available. To build a relocatable DLL, gnatdll does the following:

* gnatdll builds the base file (api.base). A base file gives the information necessary to generate relocation information for the DLL.
```
$ gnatbind -n api
$ gnatlink api -o api.jnk -mdll -Wl,--base-file,api.base
```
In addition to the base file, the `gnatlink' command generates an output file api.jnk which can be discarded. The `-mdll' switch asks `gnatlink' to generate the routines DllMain and DllMainCRTStartup that are called by the Windows loader when the DLL is loaded into memory.
* gnatdll uses dlltool (see Using dlltool) to build the export table (api.exp). The export table contains the relocation information in a form which can be used during the final link to ensure that the Windows loader is able to place the DLL anywhere in memory.
```
$ dlltool --dllname api.dll --def api.def --base-file api.base \\
          --output-exp api.exp
```
* gnatdll builds the base file using the new export table. Note that `gnatbind' must be called once again since the binder generated file has been deleted during the previous call to `gnatlink'.
```
$ gnatbind -n api
$ gnatlink api -o api.jnk api.exp -mdll
      -Wl,--base-file,api.base
```

* gnatdll builds the new export table using the new base file and generates the DLL import library libAPI.dll.a.

$ dlltool --dllname api.dll --def api.def --base-file api.base \\
          --output-exp api.exp --output-lib libAPI.a

* Finally gnatdll builds the relocatable DLL using the final export table.
```
$ gnatbind -n api
$ gnatlink api api.exp -o api.dll -mdll
```

Using dlltool

dlltool is the low-level tool used by gnatdll to build DLLs and static import libraries. This section summarizes the most common dlltool switches. The form of the dlltool command is

$ dlltool [`switches`]

dlltool switches include:

--base-file `basefile': Read the base file basefile generated by the linker. This switch is used to create a relocatable DLL.

--def `deffile': Read the definition file.

--dllname `name': Gives the name of the DLL. This switch is used to embed the name of the DLL in the static import library generated by dlltool with switch `–output-lib'.

-k: Kill @`nn' from exported names (Windows Calling Conventions for a discussion about Stdcall-style symbols.

--help: Prints the dlltool switches with a concise description.

--output-exp `exportfile': Generate an export file exportfile. The export file contains the export table (list of symbols in the DLL) and is used to create the DLL.

--output-lib `libfile': Generate a static import library libfile.

-v: Verbose mode.

--as `assembler-name': Use assembler-name as the assembler. The default is as.