GCC on OS/2 supports several extra options. They all start with -Z. With the exception of -Zomf (others?) they are affecting the linking.

• -Zcrtdll: link the C library dynamically
• -Zdll: create a dynamic link library
• -Zexe: create foo which is executable which calls foo.exe which is also created.
• -Zhigh-mem: link so that the C library calls in the program make use of "high memory". This is similiar to specifying OBJ_ANY to OS/2 API memory calls. If you use this option you should include os2safe.h as the first include file in every C file that uses OS/2 APIs.
• -Zlinker: pass option through to linker (like -Zlinker /EXEPACK:2 -Zlinker /PACKCODE)
• -Zmap: tell linker or emxbind to create a .map file that contains the addresses of all symbols
• -Zno-autoconv: switch off automatic conversion between a.out and OMF format when linking.
• -Zomf: compile and link using OMF format instead of a.out.
• -Zargs-wild: call _wildcard() (see below) automatically on startup

These are mentioned in ReleaseNotes.os2 but not sure what they do exactly:

• -Zargs-resp: ??
• -Zdll-search: ??
• -Zhigh-low: ??
• -Zno-fork: turn off the fork() function?
• -Zno-unix: non-unix like mode, affects slash handling and fork()?

These were supported options with EMX/gcc 2.8.x, not sure if they are still supported now:

• -Zbin-files: open files in binary mode by default (still supported)
• -Zbsd-signals: select the `BSD' signal processing model
• -Zmt: multithread code (now default)
• -Zmtd: multithread code, link C library dynamically
• -Zmts: multithread code, link C library statically
• -Zno-rte: create DLL without runtime environment
• -Zsmall-conv: use small, fast, and inaccurate routines for converting decimal numbers to binary and vice versa
• -Zstack: set the stack size
• -Zso: create stand-alone DLL
• -Zsys: create stand-alone OS/2 program (no emx.dll) - there's nothing similar for current libc, if you use new gcc with new libc, you always need the libcxxx.dll
• -Zsysv-signals: select the `System V' signal processing model

Finally, there are a couple of special functions which simplify porting of Unix programs:

• _wildcard (int *argc, char ***argv): Same as in EMX, i.e. it expands it's arguments like a unix shell would do (but OS/2 cmd.exe doesn't), so you typically want to use this when porting a unix command line application. Instead of adding this to a program, compilation with -Zargs-wild can be used.