Compiling a C program on Subsystem for Unix-based Applications (SUA) & Interix

by Rodney Ruddock

Overview

This paper provides an introduction to what is available and what needs to be installed to compile C programs with Subsystem for Unix-based Applications (SUA) and Interix. Some example are provided for novice programmers or programmers unaccustomed to command line compiling.

What's Available

For building C programs on SUA and Interix there are several choices of compiler. Available are gcc, Visual C, Intel and PGI.

The gcc suite of tools is available as part of the installation of the Utilities and SD for SUA/Interix. This is labeled as the "GNU SDK" when you choose the Custom Install (always recommended). The suite includes the GNU debugger gdb. The gcc suite is capable of building binary objects, binary executables and shared libraries.

Microsoft's Visual C can be used from the SUA/Interix system to produce SUA/Interix binaries (often called POSIX binaries). You can use any of the Visual C versions available as part of Visual Studio. You may also install the Visual C only package that is available for free from Microsoft. To correctly utilize Visual C two utilities are provided with SUA/Interix: cc and c89. If you are versed in the Unix-world these names will be familiar. With SUA/Interix cc and c89 provide different levels of command line option strictness. While c89 adheres strictly to the C89 standard for options and their placement, cc is more relaxed with option positions on the command line. This means cc is the most flexible when build scripts are migrating or porting to SUA/Interix.

Both the Intel and PGI C compilers require that the SDK's from the Utilities and SDK installation be installed. The SDK's provide the include files, manual pages for API's and other supporting utilities. Both are capable of producing and linking with SUA/Interix binaries. For more information about each of these offerings please visit their respective web sites.

Installing Needed Components

For a full description of what should be installed please refer to the other white papers and videos:

Note that you should install both of the SDK's: the SUA/Interix SDK and the GNU SDK. This will get you cc, c89, the gcc suite including the gdb debugger, API manual pages and shared library support (runtime).

After you have installed both SDK's then you can install the other compilers (MSVC, Intel, PGI) if you have them.

Use the Command Line

Users of a GUI for compiling and linking programs should familiarize themselves with the shell to issue the command line actions. This is good background and knowledge for you to have and clears away much of the mystism of GUI's.

Customizing Editors and Shells

From Microsoft the utilities include a couple of the basic editors (vi and ed). Some people prefer some other editors. If you have not already done so, I suggest that you install additional software packages from the SUA Community Tools Warehouse individually or via one of the Bundles. This is also true for the shells. The basic installation comes with ksh/sh and csh/tcsh (version 6.14). From the Tools Warehouse you can update tcsh to a more recent version as well as add bash and/or zsh.

Simple Example

Start any one of the shells. In the examples below I will be using sh. You can start some of the shells from the Start Menu.

Now edit a file named "hello.c" and enter the code below.

    #include 

    int
    main(void)
    {
	    printf("Hello world!\n");
    }

This program should shock no one. It gives us a familiar file to work with for compiling and linking. After saving this file run the following commands in your shell:

    $ vi hello.c
    $ gcc -o hello hello.c
    $ ./hello
    Hello World!
    $

If you have MSVC, PGI or Intel installed you can substitute "gcc" above with "cc", "c89", "pcc", etc.

Using Build Tools

Available with SUA / Interix are the familiar build tools that most sites use when building programs. This includes make, gmake, xmkmf and jam. The version of make is BSD based and has all of BSD's familiar (and very useful) extensions. gmake is GNU's version of "make" which has different extensions than BSD make.

Linking with Libraries

Of course SUA / Interix comes with several libraries located in "/usr/lib" and in "/usr/X11/lib". The largest and most familiar is libc of course. On the 32-bit systems the libraries are available as both static and shared libraries. On 64-bit systems the libraries are available (in 64-bit) as static libraries only. You can build and link 32-bit programs on the 64-bit machines if you want or need to in which case both static and shared libraries are available.

Different systems have over time blended some libraries into libc. This is simply due to more memory being available and it making developers lives a little easier. On SUA/Interix the pthreads API's are all within libc while the RPC library librpclib is still separate. You can discover or find API's that remain unlinked at the end of a build with a command line (or small script or alias) using a combination of nm and grep. For example to find the API "zaphod_head_right" in the libraries in the "/usr/lib" directory:

    $ for i  in `ls /usr/lib/lib*.a`
    > do
    > echo $i
    > nm $i | grep zaphod_head_right
    > done

Once found you can them add the link. As an example:

    $ gcc -o hello2 hello2.c -lrpclib

Default Linking Actions

With the cc and c89 commands the resulting binaries are always static binaries. That is, the binaries do not used shared libraries.

With gcc the resulting binaries use shared libraries (if available) by default. You can change this behavior by adding the gcc option "-static" at the link phase. When a resulting binary that uses shared libraries is run the shared libraries are loaded at runtime the same as on other systems; with ld.so. The ld.so that ships from Microsoft is only aware that it should search for the shared libraries in the directories "/usr/lib" and "/usr/X11/lib" plus the directories listed in the environment variable LD_LIBRARY_PATH. An enhanced verison of ls.do is available from the Tools Warehouse as part of the libdl software package. The enhanced ld.so also checks "/usr/local/lib" (the site of may shared libraries) and "/usr/local/ssl/lib" in addition to those listed previously. Also the enhance version can use the ldconfig utilities (also part of the libdl package) so you can set more default paths that all programs, run by all users will search. This can ease a lot of problems particularly when daemons are being started or the environment variable LD_LIBRARY_PATH may not or cannot be set.

Conclusion

Building C programs on SUA/Interix is virtually the same as on other Unix and Linux systems. While there are some variation you will encounter, these are no different than when moving between other systems.

Compiling a C program on Subsystem for Unix-based Applications (SUA) & Interix by Rodney Ruddock Overview This paper provides an introduction to what is available and what needs to be installed to compile C programs with Subsystem for Unix-based Applications (SUA) and Interix. Some example are provided for novice programmers or programmers unaccustomed to command line compiling. What's Available For building C programs on SUA and Interix there are several choices of compiler. Available are gcc, Visual C, Intel and PGI. The gcc suite of tools is available as part of the installation of the Utilities and SD for SUA/Interix. This is labeled as the "GNU SDK" when you choose the Custom Install (always recommended). The suite includes the GNU debugger gdb. The gcc suite is capable of building binary objects, binary executables and shared libraries. Microsoft's Visual C can be used from the SUA/Interix system to produce SUA/Interix binaries (often called POSIX binaries). You can use any of the Visual C versions available as part of Visual Studio. You may also install the Visual C only package that is available for free from Microsoft. To correctly utilize Visual C two utilities are provided with SUA/Interix: cc and c89. If you are versed in the Unix-world these names will be familiar. With SUA/Interix cc and c89 provide different levels of command line option strictness. While c89 adheres strictly to the C89 standard for options and their placement, cc is more relaxed with option positions on the command line. This means cc is the most flexible when build scripts are migrating or porting to SUA/Interix. Both the Intel and PGI C compilers require that the SDK's from the Utilities and SDK installation be installed. The SDK's provide the include files, manual pages for API's and other supporting utilities. Both are capable of producing and linking with SUA/Interix binaries. For more information about each of these offerings please visit their respective web sites. Installing Needed Components For a full description of what should be installed please refer to the other white papers and videos: Installing Commands, Utilities and Libraries (pdf file) Orientation for User, Developers and Administrators Video 1: Installation of Subsystem for Unix-based Applications Note that you should install both of the SDK's: the SUA/Interix SDK and the GNU SDK. This will get you cc, c89, the gcc suite including the gdb debugger, API manual pages and shared library support (runtime). After you have installed both SDK's then you can install the other compilers (MSVC, Intel, PGI) if you have them. Use the Command Line Users of a GUI for compiling and linking programs should familiarize themselves with the shell to issue the command line actions. This is good background and knowledge for you to have and clears away much of the mystism of GUI's. Customizing Editors and Shells From Microsoft the utilities include a couple of the basic editors (vi and ed). Some people prefer some other editors. If you have not already done so, I suggest that you install additional software packages from the SUA Community Tools Warehouse individually or via one of the Bundles. This is also true for the shells. The basic installation comes with ksh/sh and csh/tcsh (version 6.14). From the Tools Warehouse you can update tcsh to a more recent version as well as add bash and/or zsh. Simple Example Start any one of the shells. In the examples below I will be using sh. You can start some of the shells from the Start Menu. Now edit a file named "hello.c" and enter the code below. #include int main(void) { printf("Hello world!\n"); } This program should shock no one. It gives us a familiar file to work with for compiling and linking. After saving this file run the following commands in your shell: $ vi hello.c $ gcc -o hello hello.c $ ./hello Hello World! $ If you have MSVC, PGI or Intel installed you can substitute "gcc" above with "cc", "c89", "pcc", etc. Using Build Tools Available with SUA / Interix are the familiar build tools that most sites use when building programs. This includes make, gmake, xmkmf and jam. The version of make is BSD based and has all of BSD's familiar (and very useful) extensions. gmake is GNU's version of "make" which has different extensions than BSD make. Linking with Libraries Of course SUA / Interix comes with several libraries located in "/usr/lib" and in "/usr/X11/lib". The largest and most familiar is libc of course. On the 32-bit systems the libraries are available as both static and shared libraries. On 64-bit systems the libraries are available (in 64-bit) as static libraries only. You can build and link 32-bit programs on the 64-bit machines if you want or need to in which case both static and shared libraries are available. Different systems have over time blended some libraries into libc. This is simply due to more memory being available and it making developers lives a little easier. On SUA/Interix the pthreads API's are all within libc while the RPC library librpclib is still separate. You can discover or find API's that remain unlinked at the end of a build with a command line (or small script or alias) using a combination of nm and grep. For example to find the API "zaphod_head_right" in the libraries in the "/usr/lib" directory: $ for i in `ls /usr/lib/lib.a` > do > echo $i > nm $i \| grep zaphod_head_right > done Once found you can them add the link. As an example: $ gcc -o hello2 hello2.c -lrpclib Default Linking Actions With the cc and c89* commands the resulting binaries are always static binaries. That is, the binaries do not used shared libraries. With gcc the resulting binaries use shared libraries (if available) by default. You can change this behavior by adding the gcc option "-static" at the link phase. When a resulting binary that uses shared libraries is run the shared libraries are loaded at runtime the same as on other systems; with ld.so. The ld.so that ships from Microsoft is only aware that it should search for the shared libraries in the directories "/usr/lib" and "/usr/X11/lib" plus the directories listed in the environment variable LD_LIBRARY_PATH. An enhanced verison of ls.do is available from the Tools Warehouse as part of the libdl software package. The enhanced ld.so also checks "/usr/local/lib" (the site of may shared libraries) and "/usr/local/ssl/lib" in addition to those listed previously. Also the enhance version can use the ldconfig utilities (also part of the libdl package) so you can set more default paths that all programs, run by all users will search. This can ease a lot of problems particularly when daemons are being started or the environment variable LD_LIBRARY_PATH may not or cannot be set. Conclusion Building C programs on SUA/Interix is virtually the same as on other Unix and Linux systems. While there are some variation you will encounter, these are no different than when moving between other systems.
© 2009 Interop Systems Inc.