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xv6-public
提交 1afc9d3f 创建 作者: Robert Morris's avatar Robert Morris
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find out the hard way why user and kernel must have separate segment descriptors
上级 c9959978
隐藏空白字符变更
内嵌 并排
正在显示 包含 30 行增加 和 19 行删除
asm.h
浏览文件 @ 1afc9d3f
......@@ -6,6 +6,8 @@
.word 0, 0; \
.byte 0, 0, 0, 0
// The 0xC0 means the limit is in 4096-byte units
// and (for executable segments) 32-bit mode.
#define SEG_ASM(type,base,lim) \
.word (((lim) >> 12) & 0xffff), ((base) & 0xffff); \
.byte (((base) >> 16) & 0xff), (0x90 | (type)), \
......
bootasm.S
浏览文件 @ 1afc9d3f
......@@ -51,8 +51,10 @@ seta20.2:
orl $CR0_PE, %eax
movl %eax, %cr0
# Jump to next instruction, but in 32-bit code segment.
# Switches processor into 32-bit mode.
# This ljmp is how you load the CS (Code Segment) register.
# SEG_ASM produces segment descriptors with the 32-bit mode
# flag set (the D flag), so addresses and word operands will
# default to 32 bits after this jump.
ljmp $(SEG_KCODE<<3), $start32
.code32 # Assemble for 32-bit mode
......
bootother.S
浏览文件 @ 1afc9d3f
......@@ -45,8 +45,10 @@ start:
orl $CR0_PE, %eax
movl %eax, %cr0
# Jump to next instruction, but in 32-bit code segment.
# Switches processor into 32-bit mode.
# This ljmp is how you load the CS (Code Segment) register.
# SEG_ASM produces segment descriptors with the 32-bit mode
# flag set (the D flag), so addresses and word operands will
# default to 32 bits after this jump.
ljmp $(SEG_KCODE<<3), $start32
.code32 # Assemble for 32-bit mode
......
main.c
浏览文件 @ 1afc9d3f
......@@ -16,13 +16,13 @@ main(void)
{
mpinit(); // collect info about this machine
lapicinit(mpbcpu());
ksegment();
ksegment(); // set up segments
picinit(); // interrupt controller
ioapicinit(); // another interrupt controller
consoleinit(); // I/O devices & their interrupts
uartinit(); // serial port
pminit(); // physical memory for kernel
jkstack(); // Jump to mainc on a properly-allocated stack
pminit(); // discover how much memory there is
jkstack(); // call mainc() on a properly-allocated stack
}
void
......@@ -41,7 +41,7 @@ void
mainc(void)
{
cprintf("\ncpu%d: starting xv6\n\n", cpu->id);
kvmalloc(); // allocate the kernel page table
kvmalloc(); // initialze the kernel page table
pinit(); // process table
tvinit(); // trap vectors
binit(); // buffer cache
......@@ -57,8 +57,9 @@ mainc(void)
mpmain();
}
// Bootstrap processor gets here after setting up the hardware.
// Additional processors start here.
// Common CPU setup code.
// Bootstrap CPU comes here from mainc().
// Other CPUs jump here from bootother.S.
static void
mpmain(void)
{
......@@ -66,11 +67,11 @@ mpmain(void)
ksegment();
lapicinit(cpunum());
}
vminit(); // Run with paging on each processor
vminit(); // turn on paging
cprintf("cpu%d: starting\n", cpu->id);
idtinit();
idtinit(); // load idt register
xchg(&cpu->booted, 1);
scheduler();
scheduler(); // start running processes
}
static void
......@@ -85,6 +86,7 @@ bootothers(void)
// placed the start of bootother.S there.
code = (uchar *) 0x7000;
memmove(code, _binary_bootother_start, (uint)_binary_bootother_size);
for(c = cpus; c < cpus+ncpu; c++){
if(c == cpus+cpunum()) // We've started already.
continue;
......@@ -95,7 +97,7 @@ bootothers(void)
*(void**)(code-8) = mpmain;
lapicstartap(c->id, (uint)code);
// Wait for cpu to get through bootstrap.
// Wait for cpu to finish mpmain()
while(c->booted == 0)
;
}
......
proc.h
浏览文件 @ 1afc9d3f
......@@ -3,8 +3,8 @@
#define SEG_KCODE 1 // kernel code
#define SEG_KDATA 2 // kernel data+stack
#define SEG_KCPU 3 // kernel per-cpu data
#define SEG_UCODE 4
#define SEG_UDATA 5
#define SEG_UCODE 4 // user code
#define SEG_UDATA 5 // user data+stack
#define SEG_TSS 6 // this process's task state
#define NSEGS 7
......
vm.c
浏览文件 @ 1afc9d3f
......@@ -93,12 +93,15 @@ ksegment(void)
{
struct cpu *c;
// Map once virtual addresses to linear addresses using identity map
// Map virtual addresses to linear addresses using identity map.
// Cannot share a CODE descriptor for both kernel and user
// because it would have to have DPL_USR, but the CPU forbids
// an interrupt from CPL=0 to DPL=3.
c = &cpus[cpunum()];
c->gdt[SEG_KCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, 0);
c->gdt[SEG_KDATA] = SEG(STA_W, 0, 0xffffffff, 0);
c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, 0x0, 0xffffffff, DPL_USER);
c->gdt[SEG_UDATA] = SEG(STA_W, 0x0, 0xffffffff, DPL_USER);
c->gdt[SEG_UCODE] = SEG(STA_X|STA_R, 0, 0xffffffff, DPL_USER);
c->gdt[SEG_UDATA] = SEG(STA_W, 0, 0xffffffff, DPL_USER);
// map cpu, and curproc
c->gdt[SEG_KCPU] = SEG(STA_W, &c->cpu, 8, 0);
......
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