diff -up Coro-5.25/Coro/Makefile.PL.ucontext Coro-5.25/Coro/Makefile.PL
--- Coro-5.25/Coro/Makefile.PL.ucontext	2011-01-10 11:29:04.000000000 +0100
+++ Coro-5.25/Coro/Makefile.PL	2011-01-10 11:29:18.000000000 +0100
@@ -49,7 +49,7 @@ if (exists $ENV{CORO_INTERFACE}) {
 
 } elsif ($^O =~ /linux/) {
    # everything "just works", as expected
-   $iface = $iface_asm || "s";
+   $iface = $iface_asm || "u";
 
 } elsif ($^O =~ /freebsd/) {
    # FreeBSD 4.x has ucontext.h but no makecontext et al. (see BUGS section of