kern/amd64: Implement syscall domains and windows

A syscall domain in the L5 kernel is a fixed list of "syscall windows",
each syscall window represents a specific platform and/or syscall model.
A platform latch within each domain determines which window / platform
should be visible. Since syscall domains are per-process, these changes
are local to their respective processes.

Signed-off-by: Ian Moffett <ian@osmora.org>

4 files changed, 94 insertions, 3 deletions

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_ */