Make sysexit and trapret paths the same, so that forkret can return through

either path.  This helped tracking down a bug: use 144 instead of 32 to find cs
in trapframe so that gs is correctly saved and restored.

For good measure update linker script, because newer versions of GCC sometimes
places symbols passed end.

1 files changed, 12 insertions, 4 deletions

diff --git a/proc.c b/proc.c
index 58ae948..3ab23f4 100644
--- a/proc.c
+++ b/proc.c
@@ -6,7 +6,6 @@
 #include "x86.h"
 #include "proc.h"
 #include "spinlock.h"
-#include "msr.h"
 
 struct {
   struct spinlock lock;
@@ -17,7 +16,11 @@ static struct proc *initproc;
 
 int nextpid = 1;
 extern void forkret(void);
+
+// we can return two ways out of the kernel and
+// for new processes we can choose either way
 extern void sysexit(void);
+extern void trapret(void);
 
 static void wakeup1(void *chan);
 
@@ -101,6 +104,10 @@ found:
 
   // Leave room for trap frame.
   sp -= sizeof *p->tf;
+
+  if ((uint64) sp % 16)
+    panic("misaligned sp");
+
   p->tf = (struct trapframe*)sp;
 
   // Set up new context to start executing at forkret,
@@ -132,6 +139,8 @@ userinit(void)
   inituvm(p->pgdir, _binary_initcode_start, (uint64)_binary_initcode_size);
   p->sz = PGSIZE;
   memset(p->tf, 0, sizeof(*p->tf));
+  p->tf->cs = UCSEG | 0x3;
+  p->tf->ss = UDSEG | 0x3;
   p->tf->r11 = FL_IF;
   p->tf->rsp = PGSIZE;
   p->tf->rcx = 0;  // beginning of initcode.S
@@ -321,12 +330,12 @@ scheduler(void)
 {
   struct proc *p;
   struct cpu *c = mycpu();
+   
   c->proc = 0;
-  
   for(;;){
     // Enable interrupts on this processor.
     sti();
-
+    
     // Loop over process table looking for process to run.
     acquire(&ptable.lock);
     for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
@@ -336,7 +345,6 @@ scheduler(void)
       // Switch to chosen process.  It is the process's job
       // to release ptable.lock and then reacquire it
       // before jumping back to us.
-
       c->proc = p;
       switchuvm(p);
       p->state = RUNNING;