From 810b5c49ebfb3398a8d9a89dedba6b97cb8688b1 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Wed, 15 Oct 2025 19:02:52 -0400
Subject: kern/amd64: Introduce kernel threads

Introduces kernel threads. by using the proc_ktd() function, one can
spawn a CPL 0 running thread to the desired code.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 src/sys/arch/amd64/os/os_proc.c | 10 ++++++++--
 src/sys/include/sys/proc.h      | 12 ++++++++++++
 src/sys/os/os_proc.c            | 30 ++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 2 deletions(-)

(limited to 'src/sys')

diff --git a/src/sys/arch/amd64/os/os_proc.c b/src/sys/arch/amd64/os/os_proc.c
index 93e5d73..c658547 100644
--- a/src/sys/arch/amd64/os/os_proc.c
+++ b/src/sys/arch/amd64/os/os_proc.c
@@ -112,8 +112,14 @@ md_proc_init(struct proc *procp, int flags)
         return error;
     }
 
-    ds = USER_DS | 3;
-    cs = USER_CS | 3;
+    if (ISSET(flags, SPAWN_KTD)) {
+        ds = KERNEL_DS;
+        cs = KERNEL_CS;
+        procp->flags |= PROC_KTD;
+    } else {
+        ds = USER_DS | 3;
+        cs = USER_CS | 3;
+    }
 
     /*
      * Set up the mapping specifier, we'll use zero
diff --git a/src/sys/include/sys/proc.h b/src/sys/include/sys/proc.h
index 618ddf3..f23c0b0 100644
--- a/src/sys/include/sys/proc.h
+++ b/src/sys/include/sys/proc.h
@@ -101,6 +101,10 @@ struct proc {
 
 #define PROC_EXITING BIT(0)     /* Process is exiting */
 #define PROC_SLEEPING BIT(1)    /* Process is sleeping */
+#define PROC_KTD BIT(2)         /* Process is kernel thread */
+
+/* Flags for PROC_SPAWN */
+#define SPAWN_KTD BIT(0)        /* Spawn kernel thread */
 
 /*
  * Initialize a process into a basic minimal
@@ -135,6 +139,14 @@ struct proc *proc_self(void);
  */
 int proc_add_range(struct proc *procp, vaddr_t va, paddr_t pa, size_t len);
 
+/*
+ * Spawn a kernel thread
+ *
+ * @procp_res: Result is written here
+ * @fn: Function where kernel thread should end up
+ */
+int proc_ktd(struct proc **procp_res, void(*fn)(void *));
+
 /*
  * Kill a process with a specific status code
  *
diff --git a/src/sys/os/os_proc.c b/src/sys/os/os_proc.c
index 582c077..a8f49d7 100644
--- a/src/sys/os/os_proc.c
+++ b/src/sys/os/os_proc.c
@@ -393,6 +393,36 @@ proc_spawn(const char *path, struct penv_blk *envbp)
     return proc->pid;
 }
 
+int
+proc_ktd(struct proc **procp_res, void(*fn)(void *))
+{
+    struct proc *proc;
+    struct pcore *core;
+
+    if (procp_res == NULL || fn == NULL) {
+        return -EINVAL;
+    }
+
+    proc = kalloc(sizeof(*proc));
+    if (proc == NULL) {
+        return -ENOMEM;
+    }
+
+    core = cpu_sched();
+    if (core == NULL) {
+        kfree(proc);
+        return -EIO;
+    }
+
+    proc_init(proc, SPAWN_KTD);
+    md_set_ip(proc, (uintptr_t)fn);
+    sched_enq(&core->scq, proc);
+
+    *procp_res = proc;
+    TAILQ_INSERT_TAIL(&procq, proc, lup_link);
+    return 0;
+}
+
 /*
  * ARG0: Pathname to spawn
  * ARG1: Process environment block
-- 
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