From c100d9ee2d7d02253b55349bf55796efb3be5699 Mon Sep 17 00:00:00 2001
From: kolya <kolya>
Date: Wed, 15 Oct 2008 05:14:10 +0000
Subject: [PATCH] cleaner swtch.S
---
defs.h | 2 +-
proc.c | 8 ++++----
proc.h | 26 +++++++++++---------------
swtch.S | 36 +++++++++++++++---------------------
4 files changed, 31 insertions(+), 41 deletions(-)
diff --git a/defs.h b/defs.h
index 661f761..a472b2e 100644
--- a/defs.h
+++ b/defs.h
@@ -107,7 +107,7 @@ 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*);
diff --git a/proc.c b/proc.c
index fdd633d..5ecf474 100644
--- a/proc.c
+++ b/proc.c
@@ -137,9 +137,9 @@ copyproc(struct proc *p)
}
// Set up new context to start executing at forkret (see below).
- memset(&np->context, 0, sizeof(np->context));
- np->context.eip = (uint)forkret;
- np->context.esp = (uint)np->tf;
+ np->context = (struct context *)np->tf - 1;
+ memset(np->context, 0, sizeof(*np->context));
+ np->context->eip = (uint)forkret;
// Clear %eax so that fork system call returns 0 in child.
np->tf->eax = 0;
@@ -477,7 +477,7 @@ procdump(void)
state = "???";
cprintf("%d %s %s", p->pid, state, p->name);
if(p->state == SLEEPING){
- getcallerpcs((uint*)p->context.ebp+2, pc);
+ getcallerpcs((uint*)p->context->ebp+2, pc);
for(j=0; j<10 && pc[j] != 0; j++)
cprintf(" %p", pc[j]);
}
diff --git a/proc.h b/proc.h
index 502361d..41860c6 100644
--- a/proc.h
+++ b/proc.h
@@ -7,21 +7,17 @@
#define NSEGS 6
// Saved registers for kernel context switches.
-// Don't need to save all the %fs etc. segment registers,
+// Don't need to save all the segment registers (%cs, etc),
// because they are constant across kernel contexts.
-// Save all the regular registers so we don't need to care
-// which are caller save, but not the return register %eax.
-// (Not saving %eax just simplifies the switching code.)
+// Stack pointer is encoded in the address of context,
+// which must be placed at the bottom of the stack.
// The layout of context must match code in swtch.S.
struct context {
- int eip;
- int esp;
- int ebx;
- int ecx;
- int edx;
- int esi;
- int edi;
- int ebp;
+ uint edi;
+ uint esi;
+ uint ebx;
+ uint ebp;
+ uint eip;
};
enum proc_state { UNUSED, EMBRYO, SLEEPING, RUNNABLE, RUNNING, ZOMBIE };
@@ -38,8 +34,8 @@ struct proc {
int killed; // If non-zero, have been killed
struct file *ofile[NOFILE]; // Open files
struct inode *cwd; // Current directory
- struct context context; // Switch here to run process
- struct trapframe *tf; // Trap frame for current interrupt
+ struct context *context; // Switch here to run process
+ struct trapframe *tf; // Trap frame for current syscall
char name[16]; // Process name (debugging)
};
@@ -53,7 +49,7 @@ struct proc {
struct cpu {
uchar apicid; // Local APIC ID
struct proc *curproc; // Process currently running.
- struct context context; // Switch here to enter scheduler
+ struct context *context; // Switch here to enter scheduler
struct taskstate ts; // Used by x86 to find stack for interrupt
struct segdesc gdt[NSEGS]; // x86 global descriptor table
volatile uint booted; // Has the CPU started?
diff --git a/swtch.S b/swtch.S
index 786e9ac..ada98f3 100644
--- a/swtch.S
+++ b/swtch.S
@@ -1,32 +1,26 @@
-# void swtch(struct context *old, struct context *new);
+# void swtch(struct context **old, struct context **new);
#
# Save current register context in old
# and then load register context from new.
.globl swtch
swtch:
- # Save old registers
movl 4(%esp), %eax
+ movl 8(%esp), %edx
- popl 0(%eax) # %eip
- movl %esp, 4(%eax)
- movl %ebx, 8(%eax)
- movl %ecx, 12(%eax)
- movl %edx, 16(%eax)
- movl %esi, 20(%eax)
- movl %edi, 24(%eax)
- movl %ebp, 28(%eax)
+ # Save old callee-save registers
+ pushl %ebp
+ pushl %ebx
+ pushl %esi
+ pushl %edi
- # Load new registers
- movl 4(%esp), %eax # not 8(%esp) - popped return address above
-
- movl 28(%eax), %ebp
- movl 24(%eax), %edi
- movl 20(%eax), %esi
- movl 16(%eax), %edx
- movl 12(%eax), %ecx
- movl 8(%eax), %ebx
- movl 4(%eax), %esp
- pushl 0(%eax) # %eip
+ # Switch stacks
+ movl %esp, (%eax)
+ movl (%edx), %esp
+ # Load new callee-save registers
+ popl %edi
+ popl %esi
+ popl %ebx
+ popl %ebp
ret
--
GitLab