From 45ab1dd925162659d59d65a95105120d9dc96978 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Fri, 28 Jun 2024 23:12:32 -0400
Subject: kernel/amd64: Focus md_td_init() to fork MD code

Rename md_td_init() to md_fork() and change up what it does to keep
things as simple as possible.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/amd64/proc_machdep.c | 23 ++++++++++-------------
 sys/include/sys/proc.h              |  2 +-
 sys/kern/init_main.c                |  3 ---
 sys/kern/kern_fork.c                |  8 +-------
 4 files changed, 12 insertions(+), 24 deletions(-)

diff --git a/sys/arch/amd64/amd64/proc_machdep.c b/sys/arch/amd64/amd64/proc_machdep.c
index eb3866a..d2eb599 100644
--- a/sys/arch/amd64/amd64/proc_machdep.c
+++ b/sys/arch/amd64/amd64/proc_machdep.c
@@ -46,12 +46,12 @@
  * @ip: Instruction pointer.
  */
 int
-md_td_init(struct proc *p, struct proc *parent, uintptr_t ip)
+md_fork(struct proc *p, struct proc *parent, uintptr_t ip)
 {
     uintptr_t stack_base;
-    struct trapframe *tfp, *parent_tfp;
+    struct trapframe *tfp;
     struct pcb *pcbp;
-    uint8_t rpl;
+    uint8_t rpl = 0;
     int error;
 
     tfp = &p->tf;
@@ -61,18 +61,15 @@ md_td_init(struct proc *p, struct proc *parent, uintptr_t ip)
     if ((error = pmap_new_vas(&pcbp->addrsp)) != 0)
         return error;
 
+    memcpy(tfp, &parent->tf, sizeof(p->tf));
+
     /*
-     * If parent is NULL, assume kernel space and zero the
-     * trapframe. Otherwise we can just set it up normally.
+     * Kernel threads cannot be on the lower half.
+     * If 'ip' is on the lower half, assume that it
+     * is a userspace program and set RPL to ring 3.
      */
-    if (parent == NULL) {
-        rpl = 0;
-        memset(tfp, 0, sizeof(*tfp));
-    } else {
-        parent_tfp = &parent->tf;
-        rpl = parent_tfp->cs & 3;
-        memcpy(tfp, &parent->tf, sizeof(*tfp));
-    }
+    if (ip < VM_HIGHER_HALF)
+        rpl = 3;
 
     /*
      * RPL being 3 indicates that the parent thread is in
diff --git a/sys/include/sys/proc.h b/sys/include/sys/proc.h
index c74bca5..684742a 100644
--- a/sys/include/sys/proc.h
+++ b/sys/include/sys/proc.h
@@ -52,7 +52,7 @@ struct proc {
 };
 
 struct proc *this_td(void);
-int md_td_init(struct proc *p, struct proc *parent, uintptr_t ip);
+int md_fork(struct proc *p, struct proc *parent, uintptr_t ip);
 int fork1(struct proc *cur, int flags, void(*ip)(void), struct proc **newprocp);
 
 #endif  /* _KERNEL */
diff --git a/sys/kern/init_main.c b/sys/kern/init_main.c
index df955ee..a5bdf1c 100644
--- a/sys/kern/init_main.c
+++ b/sys/kern/init_main.c
@@ -56,9 +56,6 @@ main(void)
     /* Startup the BSP */
     cpu_startup(&g_bsp_ci);
 
-    /* Init process 0 */
-    md_td_init(&proc0, NULL, 0);
-
     /* Init the virtual file system */
     vfs_init();
 
diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c
index 64e0caf..ce5f3a6 100644
--- a/sys/kern/kern_fork.c
+++ b/sys/kern/kern_fork.c
@@ -54,13 +54,7 @@ fork1(struct proc *cur, int flags, void(*ip)(void), struct proc **newprocp)
     if (newproc == NULL)
         return -ENOMEM;
 
-    /*
-     * We want to zero the proc to ensure it is in known
-     * state. We then want to initialize machine dependent
-     * fields.
-     */
-    memset(newproc, 0, sizeof(*newproc));
-    status = md_td_init(newproc, cur, (uintptr_t)ip);
+    status = md_fork(newproc, cur, (uintptr_t)ip);
     if (status != 0)
         goto done;
 
-- 
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