From 2c5f7aba38f8e7207a81fdef36d7720bda9dc4e5 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@swtch.com>
Date: Sat, 11 Jul 2009 19:28:29 -0700
Subject: [PATCH] initproc, usegment, swtch tweaks
---
defs.h | 5 ++--
proc.c | 85 +++++++++++++++++++++++++------------------------------
swtch.S | 8 ++++--
trapasm.S | 8 ------
4 files changed, 46 insertions(+), 60 deletions(-)
diff --git a/defs.h b/defs.h
index cb47716..09fa467 100644
--- a/defs.h
+++ b/defs.h
@@ -52,7 +52,7 @@ int writei(struct inode*, char*, uint, uint);
// ide.c
void ideinit(void);
void ideintr(void);
-void iderw(struct buf *);
+void iderw(struct buf*);
// ioapic.c
void ioapicenable(int irq, int cpu);
@@ -109,7 +109,7 @@ void wakeup(void*);
void yield(void);
// swtch.S
-void swtch(struct context**, struct context**);
+void swtch(struct context**, struct context*);
// spinlock.c
void acquire(struct spinlock*);
@@ -151,7 +151,6 @@ void uartinit(void);
void uartintr(void);
void uartputc(int);
-
// number of elements in fixed-size array
#define NELEM(x) (sizeof(x)/sizeof((x)[0]))
diff --git a/proc.c b/proc.c
index 554ad28..aa6c4ec 100644
--- a/proc.c
+++ b/proc.c
@@ -15,7 +15,7 @@ static struct proc *initproc;
int nextpid = 1;
extern void forkret(void);
-extern void forkret1(struct trapframe*);
+extern void trapret(void);
void
pinit(void)
@@ -30,19 +30,18 @@ static struct proc*
allocproc(void)
{
struct proc *p;
+ char *sp;
acquire(&ptable.lock);
- for(p = ptable.proc; p < &ptable.proc[NPROC]; p++){
- if(p->state == UNUSED){
- p->state = EMBRYO;
- p->pid = nextpid++;
+ for(p = ptable.proc; p < &ptable.proc[NPROC]; p++)
+ if(p->state == UNUSED)
goto found;
- }
- }
release(&ptable.lock);
return 0;
found:
+ p->state = EMBRYO;
+ p->pid = nextpid++;
release(&ptable.lock);
// Allocate kernel stack if necessary.
@@ -50,11 +49,20 @@ found:
p->state = UNUSED;
return 0;
}
- p->tf = (struct trapframe*)(p->kstack + KSTACKSIZE) - 1;
-
- // Set up new context to start executing at forkret (see below).
- p->context = (struct context *)p->tf - 1;
- memset(p->context, 0, sizeof(*p->context));
+ sp = p->kstack + KSTACKSIZE;
+
+ // Leave room for trap frame.
+ sp -= sizeof *p->tf;
+ p->tf = (struct trapframe*)sp;
+
+ // Set up new context to start executing at forkret,
+ // which returns to trapret (see below).
+ sp -= 4;
+ *(uint*)sp = (uint)trapret;
+
+ sp -= sizeof *p->context;
+ p->context = (struct context*)sp;
+ memset(p->context, 0, sizeof *p->context);
p->context->eip = (uint)forkret;
return p;
}
@@ -79,19 +87,16 @@ growproc(int n)
}
// Set up CPU's kernel segment descriptors.
+// Run once at boot time on each CPU.
void
ksegment(void)
{
struct cpu *c1;
c1 = &cpus[cpu()];
- c1->gdt[0] = SEG_NULL;
c1->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0x100000 + 64*1024-1, 0);
c1->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
- c1->gdt[SEG_KCPU] = SEG(STA_W, (uint)&c1->tls+sizeof(c1->tls), 0xffffffff, 0);
- c1->gdt[SEG_UCODE] = SEG_NULL;
- c1->gdt[SEG_UDATA] = SEG_NULL;
- c1->gdt[SEG_TSS] = SEG_NULL;
+ c1->gdt[SEG_KCPU] = SEG(STA_W, (uint)(&c1->tls+1), 0xffffffff, 0);
lgdt(c1->gdt, sizeof(c1->gdt));
loadfsgs(SEG_KCPU << 3);
@@ -106,23 +111,12 @@ void
usegment(void)
{
pushcli();
- c->ts.ss0 = SEG_KDATA << 3;
- if(cp)
- c->ts.esp0 = (uint)(cp->kstack + KSTACKSIZE);
- else
- c->ts.esp0 = 0xffffffff;
-
- if(cp){
- c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (uint)cp->mem, cp->sz-1, DPL_USER);
- c->gdt[SEG_UDATA] = SEG(STA_W, (uint)cp->mem, cp->sz-1, DPL_USER);
- } else {
- c->gdt[SEG_UCODE] = SEG_NULL;
- c->gdt[SEG_UDATA] = SEG_NULL;
- }
+ c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, (uint)cp->mem, cp->sz-1, DPL_USER);
+ c->gdt[SEG_UDATA] = SEG(STA_W, (uint)cp->mem, cp->sz-1, DPL_USER);
c->gdt[SEG_TSS] = SEG16(STS_T32A, (uint)&c->ts, sizeof(c->ts)-1, 0);
c->gdt[SEG_TSS].s = 0;
-
- lgdt(c->gdt, sizeof(c->gdt));
+ c->ts.ss0 = SEG_KDATA << 3;
+ c->ts.esp0 = (uint)cp->kstack + KSTACKSIZE;
ltr(SEG_TSS << 3);
popcli();
}
@@ -171,7 +165,7 @@ void
userinit(void)
{
struct proc *p;
- extern uchar _binary_initcode_start[], _binary_initcode_size[];
+ extern char _binary_initcode_start[], _binary_initcode_size[];
p = allocproc();
initproc = p;
@@ -179,6 +173,7 @@ userinit(void)
// Initialize memory from initcode.S
p->sz = PAGE;
p->mem = kalloc(p->sz);
+ memset(p->mem, 0, p->sz);
memmove(p->mem, _binary_initcode_start, (int)_binary_initcode_size);
memset(p->tf, 0, sizeof(*p->tf));
@@ -210,7 +205,7 @@ scheduler(void)
struct proc *p;
for(;;){
- // Enable interrupts on this processor, in lieu of saving intena.
+ // Enable interrupts on this processor.
sti();
// Loop over process table looking for process to run.
@@ -225,36 +220,35 @@ scheduler(void)
cp = p;
usegment();
p->state = RUNNING;
- swtch(&c->context, &p->context);
+ swtch(&c->context, p->context);
// Process is done running for now.
// It should have changed its p->state before coming back.
cp = 0;
- usegment();
}
release(&ptable.lock);
}
}
-// Enter scheduler. Must already hold ptable.lock
+// Enter scheduler. Must hold only ptable.lock
// and have changed cp->state.
void
sched(void)
{
int intena;
- if(readeflags()&FL_IF)
- panic("sched interruptible");
- if(cp->state == RUNNING)
- panic("sched running");
if(!holding(&ptable.lock))
panic("sched ptable.lock");
if(c->ncli != 1)
panic("sched locks");
+ if(cp->state == RUNNING)
+ panic("sched running");
+ if(readeflags()&FL_IF)
+ panic("sched interruptible");
intena = c->intena;
- swtch(&cp->context, &c->context);
+ swtch(&cp->context, c->context);
c->intena = intena;
}
@@ -262,7 +256,7 @@ sched(void)
void
yield(void)
{
- acquire(&ptable.lock);
+ acquire(&ptable.lock); //DOC: yieldlock
cp->state = RUNNABLE;
sched();
release(&ptable.lock);
@@ -275,9 +269,8 @@ forkret(void)
{
// Still holding ptable.lock from scheduler.
release(&ptable.lock);
-
- // Jump into assembly, never to return.
- forkret1(cp->tf);
+
+ // Return to "caller", actually trapret (see allocproc).
}
// Atomically release lock and sleep on chan.
diff --git a/swtch.S b/swtch.S
index ada98f3..8751317 100644
--- a/swtch.S
+++ b/swtch.S
@@ -1,5 +1,7 @@
-# void swtch(struct context **old, struct context **new);
-#
+# Context switch
+#
+# void swtch(struct context **old, struct context *new);
+#
# Save current register context in old
# and then load register context from new.
@@ -16,7 +18,7 @@ swtch:
# Switch stacks
movl %esp, (%eax)
- movl (%edx), %esp
+ movl %edx, %esp
# Load new callee-save registers
popl %edi
diff --git a/trapasm.S b/trapasm.S
index 983163d..1cb2ce6 100644
--- a/trapasm.S
+++ b/trapasm.S
@@ -35,11 +35,3 @@ trapret:
popl %ds
addl $0x8, %esp # trapno and errcode
iret
-
- # A forked process switches to user mode by calling
- # forkret1(tf), where tf is the trap frame to use.
-.globl forkret1
-forkret1:
- movl 4(%esp), %esp
- jmp trapret
-
--
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