diff -buNr configure.org configure
--- configure.org	2008-09-24 13:45:48.000000000 +0900
+++ configure	2008-09-28 12:04:34.000000000 +0900
@@ -234,6 +234,13 @@
     LDFLAGS="$LDFLAGS -lm"
     HAVE_GETOPT_LONG=0
     ;;
+  os2*)
+    SYS="OS2"
+    EXE=".exe"
+    DEVNULL="NUL"
+    CFLAGS="$CFLAGS -DHAVE_MALLOC_H"
+    LDFLAGS="$LDFLAGS -Zbin-files"
+    ;;
   *)
     echo "Unknown system $host, edit the configure"
     exit 1
@@ -249,6 +256,8 @@
       ASFLAGS="$ASFLAGS -f macho -DPREFIX"
     elif [ "$SYS" = MINGW ]; then
       ASFLAGS="$ASFLAGS -f win32 -DPREFIX"
+    elif [ "$SYS" = OS2 ]; then
+      ASFLAGS="$ASFLAGS -f aout -DPREFIX"
     else
       ASFLAGS="$ASFLAGS -f elf"
     fi
@@ -438,6 +447,7 @@
 HAVE_GETOPT_LONG=$HAVE_GETOPT_LONG
 DEVNULL=$DEVNULL
 ECHON=$ECHON
+INSTALL=${INSTALL-install}
 EOF

 $ECHON 'CONFIGURE_ARGS=' >> config.mak
@@ -458,6 +468,12 @@
         echo "SOSUFFIX=dylib" >> config.mak
         echo "SONAME=libx264.$API.dylib" >> config.mak
         echo 'SOFLAGS=-dynamiclib -Wl,-single_module -Wl,-read_only_relocs,suppress -install_name $(DESTDIR)$(libdir)/$(SONAME)' >> config.mak
+    elif [ "$SYS" = "OS2" ]; then
+        echo "SOSUFFIX=dll" >> config.mak
+        echo "SONAME=libx264.dll" >> config.mak
+        echo "SODEF=libx264.def" >> config.mak
+        echo "IMPLIBNAME=libx264_dll.a" >> config.mak
+        echo 'SOFLAGS=-Zdll $(SODEF)' >> config.mak
     else
         echo "SOSUFFIX=so" >> config.mak
         echo "SONAME=libx264.so.$API" >> config.mak
diff -buNr Makefile.org Makefile
--- Makefile.org	2008-09-24 13:45:48.000000000 +0900
+++ Makefile	2008-09-28 18:09:28.000000000 +0900
@@ -42,7 +42,7 @@
 SRCS   += common/x86/mc-c.c common/x86/predict-c.c
 OBJASM  = $(ASMSRC:%.asm=%.o)
 $(OBJASM): common/x86/x86inc.asm common/x86/x86util.asm
-checkasm: tools/checkasm-a.o
+checkasm$(EXE): tools/checkasm-a.o
 endif
 endif

@@ -78,6 +78,13 @@
 	ranlib libx264.a

 $(SONAME): .depend $(OBJS) $(OBJASM)
+ifeq ($(SYS),OS2)
+	echo "LIBRARY $(SONAME:.$(SOSUFFIX)=)" > $(SODEF)
+	echo "DATA MULTIPLE NONSHARED" >> $(SODEF)
+	echo "EXPORTS" >> $(SODEF)
+	emxexp $(OBJS) $(OBJASM) >> $(SODEF)
+	emximp -o $(IMPLIBNAME) $(SODEF)
+endif
 	$(CC) -shared -o $@ $(OBJS) $(OBJASM) $(SOFLAGS) $(LDFLAGS)

 x264$(EXE): $(OBJCLI) libx264.a
@@ -86,7 +93,7 @@
 libx264gtk.a: muxers.o libx264.a
 	$(MAKE) -C gtk

-checkasm: tools/checkasm.o libx264.a
+checkasm$(EXE): tools/checkasm.o libx264.a
 	$(CC) -o $@ $+ $(LDFLAGS)

 %.o: %.asm
@@ -138,8 +145,8 @@
 endif

 clean:
-	rm -f $(OBJS) $(OBJASM) $(OBJCLI) $(SONAME) *.a x264 x264.exe .depend TAGS
-	rm -f checkasm checkasm.exe tools/checkasm.o
+	rm -f $(OBJS) $(OBJASM) $(OBJCLI) $(SONAME) $(SODEF) *.a x264 x264.exe .depend TAGS
+	rm -f checkasm checkasm.exe tools/checkasm.o tools/checkasm-a.o
 	rm -f tools/avc2avi tools/avc2avi.exe tools/avc2avi.o
 	rm -f $(SRC2:%.c=%.gcda) $(SRC2:%.c=%.gcno)
 	- sed -e 's/ *-fprofile-\(generate\|use\)//g' config.mak > config.mak2 && mv config.mak2 config.mak
@@ -151,20 +158,22 @@
 	$(MAKE) -C gtk distclean

 install: x264$(EXE) $(SONAME)
-	install -d $(DESTDIR)$(bindir) $(DESTDIR)$(includedir)
-	install -d $(DESTDIR)$(libdir) $(DESTDIR)$(libdir)/pkgconfig
-	install -m 644 x264.h $(DESTDIR)$(includedir)
-	install -m 644 libx264.a $(DESTDIR)$(libdir)
-	install -m 644 x264.pc $(DESTDIR)$(libdir)/pkgconfig
-	install x264$(EXE) $(DESTDIR)$(bindir)
+	$(INSTALL) -d $(DESTDIR)$(bindir) $(DESTDIR)$(includedir)
+	$(INSTALL) -d $(DESTDIR)$(libdir) $(DESTDIR)$(libdir)/pkgconfig
+	$(INSTALL) -m 644 x264.h $(DESTDIR)$(includedir)
+	$(INSTALL) -m 644 libx264.a $(DESTDIR)$(libdir)
+	$(INSTALL) -m 644 x264.pc $(DESTDIR)$(libdir)/pkgconfig
+	$(INSTALL) x264$(EXE) $(DESTDIR)$(bindir)
 	ranlib $(DESTDIR)$(libdir)/libx264.a
 ifeq ($(SYS),MINGW)
-	$(if $(SONAME), install -m 755 $(SONAME) $(DESTDIR)$(bindir))
+	$(if $(SONAME), $(INSTALL) -m 755 $(SONAME) $(DESTDIR)$(bindir))
 else
+ifneq ($(SYS),OS2)
 	$(if $(SONAME), ln -sf $(SONAME) $(DESTDIR)$(libdir)/libx264.$(SOSUFFIX))
-	$(if $(SONAME), install -m 755 $(SONAME) $(DESTDIR)$(libdir))
 endif
-	$(if $(IMPLIBNAME), install -m 644 $(IMPLIBNAME) $(DESTDIR)$(libdir))
+	$(if $(SONAME), $(INSTALL) -m 755 $(SONAME) $(DESTDIR)$(libdir))
+endif
+	$(if $(IMPLIBNAME), $(INSTALL) -m 644 $(IMPLIBNAME) $(DESTDIR)$(libdir))

 install-gtk: libx264gtk.a
 	$(MAKE) -C gtk install
@@ -173,6 +182,7 @@
 	rm -f $(DESTDIR)$(includedir)/x264.h $(DESTDIR)$(libdir)/libx264.a
 	rm -f $(DESTDIR)$(bindir)/x264 $(DESTDIR)$(libdir)/pkgconfig/x264.pc
 	$(if $(SONAME), rm -f $(DESTDIR)$(libdir)/$(SONAME) $(DESTDIR)$(libdir)/libx264.$(SOSUFFIX))
+	$(if $(IMPLIBNAME), rm -f $(DESTDIR)$(libdir)/$(IMPLIBNAME))
 	$(MAKE) -C gtk uninstall

 etags: TAGS
diff -buNr x264.c.org x264.c
--- x264.c.org	2008-09-24 13:45:48.000000000 +0900
+++ x264.c	2008-09-26 23:25:42.000000000 +0900
@@ -96,10 +96,8 @@
     pthread_win32_thread_attach_np();
 #endif

-#ifdef _WIN32
-    _setmode(_fileno(stdin), _O_BINARY);
-    _setmode(_fileno(stdout), _O_BINARY);
-#endif
+    set_bin_mode(stdin);
+    set_bin_mode(stdout);

     x264_param_default( &param );

diff -buNr common/cpu.c.org common/cpu.c
--- common/cpu.c.org	2008-09-24 13:45:48.000000000 +0900
+++ common/cpu.c	2008-09-28 12:10:42.000000000 +0900
@@ -32,6 +32,10 @@
 #include <sys/types.h>
 #include <sys/sysctl.h>
 #endif
+#ifdef SYS_OS2
+#define INCL_DOS
+#include <os2.h>
+#endif

 #include "common.h"
 #include "cpu.h"
@@ -291,6 +295,13 @@
     }
     return numberOfCPUs;

+#elif defined(SYS_OS2)
+    uint32_t numprocs = 1;
+
+    DosQuerySysInfo(QSV_NUMPROCESSORS, QSV_NUMPROCESSORS, &numprocs, sizeof(numprocs));
+
+    return numprocs;
+
 #else
     return 1;
 #endif
diff -buNr common/osdep.h.org common/osdep.h
--- common/osdep.h.org	2008-09-24 13:45:48.000000000 +0900
+++ common/osdep.h	2008-09-26 23:25:02.000000000 +0900
@@ -37,6 +37,13 @@
 #ifdef _WIN32
 #include <io.h>    // _setmode()
 #include <fcntl.h> // _O_BINARY
+#define set_bin_mode(stream) _setmode(_fileno(stream), _O_BINARY)
+#elif defined(SYS_OS2)
+#include <io.h>    // setmode()
+#include <fcntl.h> // O_BINARY
+#define set_bin_mode(stream) setmode(fileno(stream), O_BINARY)
+#else
+#define set_bin_mode(stream)
 #endif

 #ifdef _MSC_VER
diff -buNr common/x86/x86inc.asm.org common/x86/x86inc.asm
--- common/x86/x86inc.asm.org	2008-09-24 13:45:48.000000000 +0900
+++ common/x86/x86inc.asm	2008-09-25 22:13:40.000000000 +0900
@@ -26,12 +26,15 @@
 ; Name of the .rodata section.
 ; Kludge: Something on OS X fails to align .rodata even given an align attribute,
 ; so use a different read-only section.
+; Kludge: aout format does not support .rodata neither align, so use .data.
 %macro SECTION_RODATA 0
     %ifidn __OUTPUT_FORMAT__,macho64
         SECTION .text align=16
     %elifidn __OUTPUT_FORMAT__,macho
         SECTION .text align=16
         fakegot:
+    %elifidn __OUTPUT_FORMAT__,aout
+        SECTION .data
     %else
         SECTION .rodata align=16
     %endif