Changes to allow use of native x86 ELF compilers, which on my

Linux 2.4 box using gcc 3.4.6 don't seem to follow the same
conventions as the i386-jos-elf-gcc compilers.
Can run make 'TOOLPREFIX=' or edit the Makefile.

curproc[cpu()] can now be NULL, indicating that no proc is running.
This seemed safer to me than having curproc[0] and curproc[1]
both pointing at proc[0] potentially.

The old implementation of swtch depended on the stack frame layout
used inside swtch being okay to return from on the other stack
(exactly the V6 you are not expected to understand this).
It also could be called in two contexts: at boot time, to schedule
the very first process, and later, on behalf of a process, to sleep
or schedule some other process.

I split this into two functions: scheduler and swtch.

The scheduler is now a separate never-returning function, invoked
by each cpu once set up.  The scheduler looks like:

	scheduler() {
		setjmp(cpu.context);

		pick proc to schedule
		blah blah blah

		longjmp(proc.context)
	}

The new swtch is intended to be called only when curproc[cpu()] is not NULL,
that is, only on behalf of a user proc.  It does:

	swtch() {
		if(setjmp(proc.context) == 0)
			longjmp(cpu.context)
	}

to save the current proc context and then jump over to the scheduler,
running on the cpu stack.

Similarly the system call stubs are now in assembly in usys.S to avoid
needing to know the details of stack frame layout used by the compiler.

Also various changes in the debugging prints.

1 files changed, 23 insertions, 1 deletions

diff --git a/proc.h b/proc.h
index 0c748aa..b5cf015 100644
--- a/proc.h
+++ b/proc.h
@@ -16,6 +16,23 @@
 #define SEG_TSS 5   // this process's task state
 #define NSEGS 6
 
+struct jmpbuf {
+  // saved registers for kernel context switches
+  // don't need to save all the fs etc. registers because
+  // they are constant across kernel contexts
+  // save all the regular registers so we don't care which are caller save
+  // don't save eax because that's the return register
+  // layout known to swtch.S
+  int jb_ebx;
+  int jb_ecx;
+  int jb_edx;
+  int jb_esi;
+  int jb_edi;
+  int jb_esp;
+  int jb_ebp;
+  int jb_eip;
+};
+
 struct proc{
   char *mem; // start of process's physical memory
   unsigned sz; // total size of mem, including kernel stack
@@ -32,17 +49,22 @@ struct proc{
   unsigned esp; // kernel stack pointer
   unsigned ebp; // kernel frame pointer
 
+  struct jmpbuf jmpbuf;
+
   struct Trapframe *tf; // points into kstack, used to find user regs
 };
 
 extern struct proc proc[];
-extern struct proc *curproc[NCPU];
+extern struct proc *curproc[NCPU];  // can be NULL if no proc running.
+  // XXX move curproc into cpu structure?
 
 #define MPSTACK 512
 
 struct cpu {
   uint8_t apicid;       // Local APIC ID
+  struct jmpbuf jmpbuf;
   char mpstack[MPSTACK]; // per-cpu start-up stack, only used to get into main()
+  struct proc *lastproc;  // last proc scheduled on this cpu (never NULL)
 };
 
 extern struct cpu cpus[NCPU];