Index: arch/posix.h
==================================================================
--- arch/posix.h
+++ arch/posix.h
@@ -8,10 +8,20 @@
 #ifndef KIplatform_posix
 #define KIplatform_posix
 #include <k/def.h>
 #include <k/type.h>
 
+#if (!defined(KFplatform_define_constants)) && \
+    (!defined(KFplatform_define_types)) && \
+    (!defined(KFplatform_define_funcs))
+#define KFplatform_define_constants
+#define KFplatform_define_types
+#define KFplatform_define_funcs
+#endif
+
+#ifdef KFplatform_define_constants
+
 enum posix_prot {
 	posix_prot_none  = 0,
 	posix_prot_read  = 1 << 0,
 	posix_prot_write = 1 << 1,
 	posix_prot_exec  = 1 << 2
@@ -32,10 +42,13 @@
 
 	/* platform flags */
 	posix_flag_linux_hugetlb = 0x40000
 };
 
+#endif
+#ifdef KFplatform_define_types
+
 /* platform types */
 
 typedef s64 k_platform_syscall_return;
 typedef u64 k_platform_syscall_error;
 
@@ -54,12 +67,21 @@
 struct k_platform_syscall_answer {
 	k_platform_syscall_return ret;
 	k_platform_syscall_error error;
 };
 
-#include <system_calls.h>
+#endif
+
+#if defined(KFplatform_define_constants) ||\
+    defined(KFplatform_define_funcs)
+#		include <system_calls.h>
+#endif
+
+#ifdef KFplatform_define_funcs
 
 extern struct k_platform_syscall_answer
 k_platform_syscall(enum k_platform_syscall call, u8 valency, 
 		k_platform_syscall_arg args[]);
+
+#endif
 
 #endif

Index: build.sh
==================================================================
--- build.sh
+++ build.sh
@@ -22,15 +22,27 @@
 
 # TODO: make it possible for user to change
 #       default set with environment vars
 modules=(kcore kmem kstr kio kgraft kfile)
 
+# compose an arch tuple. this is used in
+# places, mostly to select the correct
+# version of assembly files for a given
+# platform (each has an arch tuple in its
+# name, following the linkage specifier)
 target=$arch.$os
 if test "$bits" != ""; then
 	target=$target.$bits
 fi
 
+# determine whether we have unix or posix
+# APIs depending on the operating system.
+# presumably if the user is running a bash
+# script there is some degree of posix
+# support available, but we might still be
+# building for windows from within cygwin
+# or whatever
 case $os in
 	lin|?bsd|and|dar|osx) posix=yes; unix=yes;;
 	hai) posix=yes; unix=no;;
 	*) posix=no; unix=no;;
 esac
@@ -80,17 +92,38 @@
 check asm "an assembler that takes Intel syntax and nasm-style-macros"
 check m4 "the path to your m4 installation"
 
 export build=$(global/build-id.sh)
 
-case $os in
-	lin) p_headers_syscall=${p_headers_syscall:-/usr/include/asm/unistd_${bits}.h}
-	p_headers_errno=${p_headers_errno:-/usr/include/asm-generic/errno.h /usr/include/asm-generic/errno-base.h};;
+if test "$p_headers_syscall" = ""; then
+	case $os in
+		lin) headers_syscall_search=(
+				/usr/include/asm/unistd_${bits}.h
+				/usr/include/asm-generic/unistd.h
+				/usr/include/*-linux-gnu/asm/unistd_${bits}.h
+			);;
 
-	fbsd) p_headers_syscall=${p_headers_syscall:-/usr/include/sys/syscall.h}
-	p_headers_errno=${p_headers_errno:-/usr/include/errno.h};;
-esac
+		fbsd) p_headers_syscall_search=(
+				/usr/include/sys/syscall.h
+			);;
+	esac
+fi
+
+if test "$p_headers_errno" = ""; then
+	case $os in
+		lin) p_headers_errno="${p_headers_errno:-/usr/include/asm-generic/errno.h /usr/include/asm-generic/errno-base.h}";;
+
+		fbsd) p_headers_errno="${p_headers_errno:-/usr/include/errno.h}";;
+	esac
+fi
+
+for f in "${headers_syscall_search[@]}"; do
+	test -e "$f" || continue
+	p_headers_syscall="$f"
+	say "using syscall headers at $f"
+	break;
+done
 
 check p_headers_syscall \
 	'the location of a header defining your syscall numbers'
 check p_headers_errno \
 	'the location of a header defining the values of each errno symbol'

Index: kcore/stop.fn.c
==================================================================
--- kcore/stop.fn.c
+++ kcore/stop.fn.c
@@ -4,14 +4,24 @@
  * a running libk program with an appropriate exit status. */
 
 #include <k/core.h>
 #include <k/def.h> // so we know what system this is
 #include <k/type.h>
-
 #ifdef KFenv_posix
-#	define STOPFN kio_posix_exit
-	extern noreturn void STOPFN(int);
-#else
-	Knoimpl(kstop)
+#	define KFplatform_define_types
+#	define KFplatform_define_constants
+#	include <posix.h>
 #endif
 
-noreturn void kstop (stat_long code) { STOPFN(code); }
+noreturn extern struct k_platform_syscall_answer
+k_platform_syscall(enum k_platform_syscall call, u8 valency, 
+		k_platform_syscall_arg args[]);
+
+noreturn void kstop(stat_long code) {
+#	ifdef KFenv_posix
+		k_platform_syscall_arg exit_code[] = { code };
+		k_platform_syscall(k_platform_syscall_exit, 1, exit_code);
+#	else
+		Knoimpl(kstop)
+#	endif
+}
+