7 files changed, 138 insertions, 11 deletions
diff --git a/src/sys/arch/amd64/cpu/trap.c b/src/sys/arch/amd64/cpu/trap.c
index 6ddc079..d023923 100644
--- a/src/sys/arch/amd64/cpu/trap.c
+++ b/src/sys/arch/amd64/cpu/trap.c
@@ -35,6 +35,7 @@
 #include <sys/param.h>
 #include <sys/cdefs.h>
 #include <sys/panic.h>
+#include <sys/cpuvar.h>
 #include <sys/syslog.h>
 #include <sys/syscall.h>
 #include <machine/trap.h>
@@ -149,6 +150,10 @@ trapframe_dump(struct trapframe *tf)
 void
 trap_syscall(struct trapframe *tf)
 {
+    struct pcore *pcore = this_core();
+    struct syscall_domain *scdp;
+    struct syscall_win *scwp;
+    struct proc *self;
     struct syscall_args scargs = {
         .arg[0] = tf->rdi,
         .arg[1] = tf->rsi,
@@ -159,8 +164,23 @@ trap_syscall(struct trapframe *tf)
         .tf = tf
     };
 
-    if (tf->rax < MAX_SYSCALLS && tf->rax > 0) {
-        tf->rax = g_sctab[tf->rax](&scargs);
+    /* Sanity check */
+    if (__unlikely(pcore == NULL)) {
+        printf("trap_syscall: pcore is NULL\n");
+        return;
+    }
+
+    /* Get the current window */
+    self = pcore->curproc;
+    scdp = &self->scdom;
+    scwp = &scdp->slots[0];
+    if (scwp->sctab == NULL && scwp->p == 0) {
+        printf("trap_syscall: no sctab (platch=%x)\n", scdp->platch);
+        return;
+    }
+
+    if (tf->rax < scwp->nimpl && tf->rax > 0) {
+        tf->rax = scwp->sctab[tf->rax](&scargs);
     }
 }
 
diff --git a/src/sys/include/compat/unix/syscall.h b/src/sys/include/compat/unix/syscall.h
new file mode 100644
index 0000000..8d0af91
--- /dev/null
+++ b/src/sys/include/compat/unix/syscall.h
@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2025 Ian Marco Moffett and L5 engineers
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the project nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef _UNIX_SYSCALL_H_
+#define _UNIX_SYSCALL_H_ 1
+
+#include <sys/proc.h>
+#include <sys/param.h>
+#include <sys/syscall.h>
+
+#ifdef _NEED_UNIX_SCTAB
+scret_t(*g_unix_sctab[])(struct syscall_args *) = {
+    [SYS_none]   = NULL,
+    [SYS_exit]   = sys_exit
+};
+
+#endif  /* !_NEED_UNIX_SCTAB */
+#endif  /* !_UNIX_SYSCALL_H_ */
diff --git a/src/sys/include/sys/limits.h b/src/sys/include/sys/limits.h
index 31aa729..d2cefb6 100644
--- a/src/sys/include/sys/limits.h
+++ b/src/sys/include/sys/limits.h
@@ -34,5 +34,7 @@
 #define NAME_MAX 256
 #define CHAR_BIT 8
 #define CPU_MAX 256
+#define SC_MAX 64       /* Max syscalls */
+#define SCWIN_MAX 2    /* Max syscall windows */
 
 #endif  /* !_SYS_LIMITS_H_ */
diff --git a/src/sys/include/sys/proc.h b/src/sys/include/sys/proc.h
index 1b1636c..109af4e 100644
--- a/src/sys/include/sys/proc.h
+++ b/src/sys/include/sys/proc.h
@@ -51,12 +51,14 @@
  * @pid: Process ID
  * @flags: State flags (see PROC_*)
  * @pcb: Process control block
+ * @scdom: Syscall domain
  * @link: TAILQ link
  */
 struct proc {
     pid_t pid;
     uint32_t flags;
     struct md_pcb pcb;
+    struct syscall_domain scdom;
     TAILQ_ENTRY(proc) link;
 };
 
diff --git a/src/sys/include/sys/syscall.h b/src/sys/include/sys/syscall.h
index 108f164..e0891e6 100644
--- a/src/sys/include/sys/syscall.h
+++ b/src/sys/include/sys/syscall.h
@@ -31,6 +31,7 @@
 #define _SYS_SYSCALL_H_
 
 #include <sys/types.h>
+#include <sys/limits.h>
 
 /*
  * Syscall numbers
@@ -52,9 +53,51 @@ struct syscall_args {
     struct trapframe *tf;
 };
 
-extern scret_t(*g_sctab[])(struct syscall_args *);
-extern const size_t MAX_SYSCALLS;
+/* Syscall callback */
+typedef scret_t(*sccb_t)(struct syscall_args *);
 
-#endif  /* _KERNEL */
+/*
+ * L5 supports syscall windows in where there can be a
+ * given set of syscalls and whatever syscall traps into
+ * kernel space will address the syscalls referenced by the
+ * current focused window. The window can be slid to change
+ * the type of syscall interface used by the running application.
+ *
+ * @sctab: Syscall table for this window
+ * @nimpl: The number of syscalls implemented
+ * @p: Present bit to indicate usability
+ */
+struct syscall_win {
+    sccb_t *sctab;
+    size_t nimpl;
+    uint8_t p : 1;
+};
+
+/*
+ * Valid platform latch constants
+ */
+typedef enum {
+    SC_PLATCH_UNIX = 0x00,
+    SC_PLATCH_L5,
+    __SC_PLATCH_MAX
+} platch_t;
 
+/*
+ * L5 provides the concept of "syscall domains". A syscall domain
+ * is a collection of syscall windows along with a sliding index
+ * known as the platform latch (`platch') to govern which syscall
+ * interface is to be used.
+ *
+ * @slots: List of windows within this domain
+ * @platch: Platform latch
+ */
+struct syscall_domain {
+    struct syscall_win slots[SCWIN_MAX];
+    platch_t platch;
+};
+
+/* Implemented platforms */
+extern scret_t(*g_unix_sctab[])(struct syscall_args *);
+extern const size_t UNIX_SCTAB_LEN;
+#endif  /* _KERNEL */
 #endif  /* !_SYS_SYSCALL_H_ */
diff --git a/src/sys/os/os_proc.c b/src/sys/os/os_proc.c
index 6880dda..329a3ea 100644
--- a/src/sys/os/os_proc.c
+++ b/src/sys/os/os_proc.c
@@ -41,13 +41,32 @@ static pid_t next_pid = 0;
 int
 proc_init(struct proc *procp, int flags)
 {
+    struct syscall_domain *scdp;
+    struct syscall_win *winp;
     int error;
 
     if (procp == NULL) {
         return -EINVAL;
     }
 
+    /* Put the process in a known state */
+    scdp = &procp->scdom;
     memset(procp, 0, sizeof(*procp));
+
+    /*
+     * Initialize each platform latch
+     */
+    for (platch_t p = 0; p < __SC_PLATCH_MAX; ++p) {
+        winp = &scdp->slots[p];
+        switch (p) {
+        case SC_PLATCH_UNIX:
+            winp->p = 1;
+            winp->sctab = &g_unix_sctab[0];
+            winp->nimpl = UNIX_SCTAB_LEN;
+            break;
+        }
+    }
+
     procp->pid = atomic_inc_int(&next_pid);
     error = md_proc_init(procp, flags);
     return error;
diff --git a/src/sys/os/os_syscall.c b/src/sys/os/os_syscall.c
index 060f774..782bfb4 100644
--- a/src/sys/os/os_syscall.c
+++ b/src/sys/os/os_syscall.c
@@ -31,10 +31,7 @@
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/proc.h>
+#define _NEED_UNIX_SCTAB
+#include <compat/unix/syscall.h>
 
-scret_t(*g_sctab[])(struct syscall_args *) = {
-    [SYS_none]   = NULL,
-    [SYS_exit]   = sys_exit
-};
-
-const size_t MAX_SYSCALLS = NELEM(g_sctab);
+const size_t UNIX_SCTAB_LEN = NELEM(g_unix_sctab);