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

Browse source 
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.
This commit is contained in:
rsc 2006-07-11 01:07:40 +00:00
parent 7ea6c9d197
commit 5ce9751cab
19 changed files with 200 additions and 131 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

13
.cvsignore Normal file
View file

@ -0,0 +1,13 @@
*.asm
*.d
kernel
user1
userfs
usertests
xv6.img
vectors.S
bochsout.txt
bootblock
bootother
bootother.out
parport.out

31
Makefile
View file

@ -1,11 +1,18 @@
OBJS = main.o console.o string.o kalloc.o proc.o trapasm.o trap.o vectors.o \
syscall.o ide.o picirq.o mp.o spinlock.o fd.o pipe.o
syscall.o ide.o picirq.o mp.o spinlock.o fd.o pipe.o swtch.o
CC = i386-jos-elf-gcc
LD = i386-jos-elf-ld
OBJCOPY = i386-jos-elf-objcopy
OBJDUMP = i386-jos-elf-objdump
# Cross-compiling (e.g., on Mac OS X)
TOOLPREFIX = i386-jos-elf-
# Using native tools (e.g., on X86 Linux)
# TOOLPREFIX =
CC = $(TOOLPREFIX)gcc
LD = $(TOOLPREFIX)ld
OBJCOPY = $(TOOLPREFIX)objcopy
OBJDUMP = $(TOOLPREFIX)objdump
CFLAGS = -nostdinc -I. -O2 -Wall -MD
AS = $(TOOLPREFIX)gas
xv6.img : bootblock kernel
dd if=/dev/zero of=xv6.img count=10000
@ -31,19 +38,21 @@ kernel : $(OBJS) bootother.S user1 usertests userfs
vectors.S : vectors.pl
perl vectors.pl > vectors.S
user1 : user1.c ulib.o
ULIB = ulib.o usys.o
user1 : user1.c $(ULIB)
$(CC) -nostdinc -I. -c user1.c
$(LD) -N -e main -Ttext 0 -o user1 user1.o ulib.o
$(LD) -N -e main -Ttext 0 -o user1 user1.o $(ULIB)
$(OBJDUMP) -S user1 > user1.asm
usertests : usertests.c ulib.o
usertests : usertests.c $(ULIB)
$(CC) -nostdinc -I. -c usertests.c
$(LD) -N -e main -Ttext 0 -o usertests usertests.o ulib.o
$(LD) -N -e main -Ttext 0 -o usertests usertests.o $(ULIB)
$(OBJDUMP) -S usertests > usertests.asm
userfs : userfs.c ulib.o
userfs : userfs.c $(ULIB)
$(CC) -nostdinc -I. -c userfs.c
$(LD) -N -e main -Ttext 0 -o userfs userfs.o ulib.o
$(LD) -N -e main -Ttext 0 -o userfs userfs.o $(ULIB)
$(OBJDUMP) -S userfs > userfs.asm
ulib.o : ulib.c

2
Notes
View file

@ -1,5 +1,7 @@
bochs 2.2.6:
./configure --enable-smp --enable-disasm --enable-debugger --enable-all-optimizations --enable-4meg-pages --enable-global-pages --enable-pae --disable-reset-on-triple-fault
bochs CVS after 2.2.6:
./configure --enable-smp --enable-disasm --enable-debugger --enable-all-optimizations --enable-4meg-pages --enable-global-pages --enable-pae
bootmain.c doesn't work right if the ELF sections aren't
sector-aligned. so you can't use ld -N. and the sections may also need

2
console.c
View file

@ -106,7 +106,7 @@ cprintf(char *fmt, ...)
if(c == 'd'){
printint(*ap, 10, 1);
ap++;
} else if(c == 'x'){
} else if(c == 'x' || c == 'p'){
printint(*ap, 16, 0);
ap++;
} else if(c == '%'){

7
defs.h
View file

@ -10,11 +10,18 @@ void cons_putc(int);
// proc.c
struct proc;
struct jmpbuf;
void setupsegs(struct proc *);
struct proc * newproc(void);
void swtch(void);
void sleep(void *);
void wakeup(void *);
void scheduler(void);
// swtch.S
struct jmpbuf;
int setjmp(struct jmpbuf*);
void longjmp(struct jmpbuf*);
// trap.c
void tvinit(void);

2
dot-bochsrc
View file

@ -107,7 +107,7 @@ romimage: file=$BXSHARE/BIOS-bochs-latest, address=0xf0000
# 650Mhz Athlon K-7 with Linux 2.4.4/egcs-2.91.66 2 to 2.5 Mips
# 400Mhz Pentium II with Linux 2.0.36/egcs-1.0.3 1 to 1.8 Mips
#=======================================================================
cpu: count=1, ips=10000000
cpu: count=2, ips=10000000
#=======================================================================
# MEGS

9
main.c
View file

@ -28,8 +28,7 @@ main()
acquire_spinlock(&kernel_lock);
idtinit(); // CPU's idt
lapic_init(cpu());
curproc[cpu()] = &proc[0]; // XXX
swtch();
scheduler();
}
acpu = 1;
// clear BSS
@ -45,7 +44,7 @@ main()
// create fake process zero
p = &proc[0];
curproc[cpu()] = p;
memset(p, 0, sizeof *p);
p->state = WAITING;
p->sz = 4 * PAGE;
p->mem = kalloc(p->sz);
@ -72,8 +71,8 @@ main()
p = newproc();
// load_icode(p, _binary_usertests_start, (unsigned) _binary_usertests_size);
load_icode(p, _binary_userfs_start, (unsigned) _binary_userfs_size);
swtch();
cprintf("loaded userfs\n");
scheduler();
return 0;
}

4
mp.c
View file

@ -141,8 +141,8 @@ lapic_timerinit()
cprintf("%d: init timer\n", cpu());
lapic_write(LAPIC_TDCR, LAPIC_X1);
lapic_write(LAPIC_TIMER, LAPIC_CLKIN | LAPIC_PERIODIC | (IRQ_OFFSET + IRQ_TIMER));
lapic_write(LAPIC_TCCR, 1000000);
lapic_write(LAPIC_TICR, 1000000);
lapic_write(LAPIC_TCCR, 10000000);
lapic_write(LAPIC_TICR, 10000000);
}
void

81
proc.c
View file

@ -48,8 +48,7 @@ struct proc *
newproc()
{
struct proc *np;
struct proc *op = curproc[cpu()];
unsigned *sp;
struct proc *op;
int fd;
for(np = &proc[1]; np < &proc[NPROC]; np++)
@ -58,6 +57,11 @@ newproc()
if(np >= &proc[NPROC])
return 0;
// copy from proc[0] if we're bootstrapping
op = curproc[cpu()];
if(op == 0)
op = &proc[0];
np->pid = next_pid++;
np->ppid = op->pid;
np->sz = op->sz;
@ -76,11 +80,12 @@ newproc()
np->tf = (struct Trapframe *) (np->kstack + KSTACKSIZE - sizeof(struct Trapframe));
*(np->tf) = *(op->tf);
np->tf->tf_regs.reg_eax = 0; // so fork() returns 0 in child
sp = (unsigned *) np->tf;
*(--sp) = (unsigned) &trapret; // for return from swtch()
*(--sp) = 0; // previous bp for leave in swtch()
np->esp = (unsigned) sp;
np->ebp = (unsigned) sp;
cprintf("newproc pid=%d return to %x:%x tf-%p\n", np->pid, np->tf->tf_cs, np->tf->tf_eip, np->tf);
// set up new jmpbuf to start executing at trapret with esp pointing at tf
memset(&np->jmpbuf, 0, sizeof np->jmpbuf);
np->jmpbuf.jb_eip = (unsigned) trapret;
np->jmpbuf.jb_esp = (unsigned) np->tf - 4; // -4 for the %eip that isn't actually there
// copy file descriptors
for(fd = 0; fd < NOFILE; fd++){
@ -96,33 +101,20 @@ newproc()
return np;
}
/*
* find a runnable process and switch to it.
*/
void
swtch()
scheduler(void)
{
struct proc *np;
struct proc *op = curproc[cpu()];
unsigned sp;
struct proc *op, *np;
int i;
// force push of callee-saved registers
asm volatile("nop" : : : "%edi", "%esi", "%ebx");
cprintf("start scheduler on cpu %d jmpbuf %p\n", cpu(), &cpus[cpu()].jmpbuf);
cpus[cpu()].lastproc = &proc[0];
// save calling process's stack pointers
op->ebp = read_ebp();
op->esp = read_esp();
// don't execute on calling process's stack
sp = (unsigned) cpus[cpu()].mpstack + MPSTACK - 32;
asm volatile("movl %0, %%esp" : : "g" (sp));
asm volatile("movl %0, %%ebp" : : "g" (sp));
// gcc might store op on the stack
np = curproc[cpu()];
np = np + 1;
setjmp(&cpus[cpu()].jmpbuf);
// find a runnable process and switch to it
curproc[cpu()] = 0;
np = cpus[cpu()].lastproc + 1;
while(1){
for(i = 0; i < NPROC; i++){
if(np >= &proc[NPROC])
@ -140,33 +132,46 @@ swtch()
np = &proc[0];
}
cprintf("cpu %d swtch %x -> %x\n", cpu(), curproc[cpu()], np);
cpus[cpu()].lastproc = np;
curproc[cpu()] = np;
np->state = RUNNING;
// h/w sets busy bit in TSS descriptor sometimes, and faults
// if it's set in LTR. so clear tss descriptor busy bit.
np->gdt[SEG_TSS].sd_type = STS_T32A;
// XXX should probably have an lgdt() function in x86.h
// to confine all the inline assembly.
// XXX probably ought to lgdt on trap return too, in case
// a system call has moved a program or changed its size.
asm volatile("lgdt %0" : : "g" (np->gdt_pd.pd_lim));
ltr(SEG_TSS << 3);
// this happens to work, but probably isn't safe:
// it's not clear that np->ebp is guaranteed to evaluate
// correctly after changing the stack pointer.
asm volatile("movl %0, %%esp" : : "g" (np->esp));
asm volatile("movl %0, %%ebp" : : "g" (np->ebp));
if(0) cprintf("cpu%d: run %d esp=%p callerpc=%p\n", cpu(), np-proc);
longjmp(&np->jmpbuf);
}
// give up the cpu by switching to the scheduler,
// which runs on the per-cpu stack.
void
swtch(void)
{
struct proc *p = curproc[cpu()];
if(p == 0)
panic("swtch");
if(setjmp(&p->jmpbuf) == 0)
longjmp(&cpus[cpu()].jmpbuf);
}
void
sleep(void *chan)
{
curproc[cpu()]->chan = chan;
curproc[cpu()]->state = WAITING;
struct proc *p = curproc[cpu()];
if(p == 0)
panic("sleep");
p->chan = chan;
p->state = WAITING;
swtch();
}

24
proc.h
View file

@ -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];

21
spinlock.c
View file

@ -4,31 +4,39 @@
#include "mmu.h"
#define LOCK_FREE -1
#define DEBUG 0
uint32_t kernel_lock = LOCK_FREE;
int getcallerpc(void *v) {
return ((int*)v)[-1];
}
// lock = LOCK_FREE if free, else = cpu_id of owner CPU
void
acquire_spinlock(uint32_t* lock)
{
int cpu_id = cpu();
if (*lock == cpu_id)
return;
// on a real machine there would be a memory barrier here
if(DEBUG) cprintf("cpu%d: acquiring at %x\n", cpu_id, getcallerpc(&lock));
write_eflags(read_eflags() & ~FL_IF);
if (*lock == cpu_id)
panic("recursive lock");
while ( cmpxchg(LOCK_FREE, cpu_id, lock) != cpu_id ) { ; }
// cprintf ("acquired: %d\n", cpu_id);
if(DEBUG) cprintf("cpu%d: acquired at %x\n", cpu_id, getcallerpc(&lock));
}
void
release_spinlock(uint32_t* lock)
{
int cpu_id = cpu();
// cprintf ("release: %d\n", cpu_id);
if(DEBUG) cprintf ("cpu%d: releasing at %x\n", cpu_id, getcallerpc(&lock));
if (*lock != cpu_id)
panic("release_spinlock: releasing a lock that i don't own\n");
*lock = LOCK_FREE;
// on a real machine there would be a memory barrier here
write_eflags(read_eflags() | FL_IF);
}
@ -36,8 +44,9 @@ void
release_grant_spinlock(uint32_t* lock, int c)
{
int cpu_id = cpu();
// cprintf ("release_grant: %d -> %d\n", cpu_id, c);
if(DEBUG) cprintf ("cpu%d: release_grant to %d at %x\n", cpu_id, c, getcallerpc(&lock));
if (*lock != cpu_id)
panic("release_spinlock: releasing a lock that i don't own\n");
*lock = c;
}

37
swtch.S Normal file
View file

@ -0,0 +1,37 @@
.globl setjmp
setjmp:
movl 4(%esp), %eax
movl %ebx, 0(%eax)
movl %ecx, 4(%eax)
movl %edx, 8(%eax)
movl %esi, 12(%eax)
movl %edi, 16(%eax)
movl %esp, 20(%eax)
movl %ebp, 24(%eax)
pushl 0(%esp) /* %eip */
popl 28(%eax)
movl $0, %eax /* return value */
ret
.globl longjmp
longjmp:
movl 4(%esp), %eax
movl 0(%eax), %ebx
movl 4(%eax), %ecx
movl 8(%eax), %edx
movl 12(%eax), %esi
movl 16(%eax), %edi
movl 20(%eax), %esp
movl 24(%eax), %ebp
addl $4, %esp /* pop %eip into thin air */
pushl 28(%eax) /* push new %eip */
movl $1, %eax /* return value (appears to come from setjmp!) */
ret

3
syscall.c
View file

@ -39,7 +39,7 @@ fetcharg(int argno, int *ip)
unsigned esp;
esp = (unsigned) curproc[cpu()]->tf->tf_esp;
return fetchint(curproc[cpu()], esp + 8 + 4*argno, ip);
return fetchint(curproc[cpu()], esp + 4 + 4*argno, ip);
}
int
@ -178,6 +178,7 @@ sys_exit()
if(p->ppid == cp->pid)
p->pid = 1;
// switch into scheduler
swtch();
return 0;

8
trap.c
View file

@ -36,13 +36,15 @@ trap(struct Trapframe *tf)
int v = tf->tf_trapno;
if(tf->tf_cs == 0x8 && kernel_lock == cpu())
cprintf("cpu %d: trap from %x:%x with lock=%d\n",
cpu(), tf->tf_cs, tf->tf_eip, kernel_lock);
cprintf("cpu %d: trap %d from %x:%x with lock=%d\n",
cpu(), v, tf->tf_cs, tf->tf_eip, kernel_lock);
acquire_spinlock(&kernel_lock); // released in trapret in trapasm.S
if(v == T_SYSCALL){
struct proc *cp = curproc[cpu()];
if(cp == 0)
panic("syscall with no proc");
cp->tf = tf;
syscall();
if(cp != curproc[cpu()])
@ -51,7 +53,7 @@ trap(struct Trapframe *tf)
panic("trap ret but not RUNNING");
if(tf != cp->tf)
panic("trap ret wrong tf");
if(read_esp() < cp->kstack || read_esp() >= cp->kstack + KSTACKSIZE)
if(read_esp() < (unsigned)cp->kstack || read_esp() >= (unsigned)cp->kstack + KSTACKSIZE)
panic("trap ret esp wrong");
return;
}

5
trapasm.S
View file

@ -22,9 +22,10 @@ alltraps:
* expects ESP to point to a Trapframe
*/
trapret:
push $kernel_lock
pushl $kernel_lock
call release_spinlock
addl $4, %esp
addl $0x4, %esp
popal
popl %es
popl %ds

56
ulib.c
View file

@ -1,24 +1,3 @@
int
fork()
{
asm("mov $1, %eax");
asm("int $48");
}
int
exit()
{
asm("mov $2, %eax");
asm("int $48");
}
void
cons_putc(int c)
{
asm("mov $4, %eax");
asm("int $48");
}
int
puts(char *s)
{
@ -29,38 +8,3 @@ puts(char *s)
return i;
}
int
pipe(int fds[])
{
asm("mov $5, %eax");
asm("int $48");
}
int
read(int fd, char *buf, int n)
{
asm("mov $7, %eax");
asm("int $48");
}
int
write(int fd, char *buf, int n)
{
asm("mov $6, %eax");
asm("int $48");
}
int
close(int fd)
{
asm("mov $8, %eax");
asm("int $48");
}
int
block(void)
{
asm("mov $9, %eax");
asm("int $48");
}

1
userfs.c
View file

@ -4,5 +4,6 @@ char buf[1024];
main()
{
puts("userfs running\n");
block();
}

18
usys.S Normal file
View file

@ -0,0 +1,18 @@
#include "syscall.h"
#include "traps.h"
#define STUB(name) \
.globl name; \
name: \
movl $SYS_ ## name, %eax; \
int $T_SYSCALL; \
ret
STUB(fork)
STUB(exit)
STUB(cons_putc)
STUB(pipe)
STUB(read)
STUB(write)
STUB(close)
STUB(block)

1
x86.h
View file

@ -349,7 +349,6 @@ struct Trapframe {
uint16_t tf_padding4;
};
#define MAX_IRQS 16 // Number of IRQs
#define IRQ_OFFSET 32 // IRQ 0 corresponds to int IRQ_OFFSET