x86-qemu mpe cleanup

am/arch/x86-qemu/img/boot/main.c

@@ -4,59 +4,65 @@
 
 void readseg(unsigned char *, int, int);
 
+struct boot_info {
+  int is_ap;
+  void (*entry)();
+};
+
 void
 bootmain(void) {
-    // multi-core boot hack, should use better ways.
-    if (*(unsigned short*)(0x7c00 + 510) == 0x55aa) {
-      ((void(*)(void))*(void**)0x7010)();
-    }
-    struct ELFHeader *elf;
-    struct ProgramHeader *ph, *eph;
-    unsigned char *pa, *i;
+  volatile struct boot_info *boot = (void*)0x7000;
+  if (boot->is_ap) {
+    boot->entry();
+  }
 
-    elf = (struct ELFHeader*)0x8000;
+  struct ELFHeader *elf;
+  struct ProgramHeader *ph, *eph;
+  unsigned char *pa, *i;
 
-    readseg((unsigned char*)elf, 4096, 0);
+  elf = (struct ELFHeader*)0x8000;
 
-    ph = (struct ProgramHeader*)((char *)elf + elf->phoff);
-    eph = ph + elf->phnum;
-    for(; ph < eph; ph ++) {
-        pa = (unsigned char*)(ph->paddr);
-        readseg(pa, ph->filesz, ph->off);
-        for (i = pa + ph->filesz; i < pa + ph->memsz; *i ++ = 0);
-    }
+  readseg((unsigned char*)elf, 4096, 0);
 
-    ((void(*)(void))elf->entry)();
+  ph = (struct ProgramHeader*)((char *)elf + elf->phoff);
+  eph = ph + elf->phnum;
+  for(; ph < eph; ph ++) {
+    pa = (unsigned char*)(ph->paddr);
+    readseg(pa, ph->filesz, ph->off);
+    for (i = pa + ph->filesz; i < pa + ph->memsz; *i ++ = 0);
+  }
+
+  ((void(*)(void))elf->entry)();
 }
 
 void
 waitdisk(void) {
-    while ((in_byte(0x1F7) & 0xC0) != 0x40);
+  while ((in_byte(0x1F7) & 0xC0) != 0x40);
 }
 
 void
 readsect(volatile void *dst, int offset) {
-    int i;
-    waitdisk();
-    out_byte(0x1F2, 1);
-    out_byte(0x1F3, offset);
-    out_byte(0x1F4, offset >> 8);
-    out_byte(0x1F5, offset >> 16);
-    out_byte(0x1F6, (offset >> 24) | 0xE0);
-    out_byte(0x1F7, 0x20);
+  int i;
+  waitdisk();
+  out_byte(0x1F2, 1);
+  out_byte(0x1F3, offset);
+  out_byte(0x1F4, offset >> 8);
+  out_byte(0x1F5, offset >> 16);
+  out_byte(0x1F6, (offset >> 24) | 0xE0);
+  out_byte(0x1F7, 0x20);
 
-    waitdisk();
-    for (i = 0; i < SECTSIZE / 4; i ++) {
-        ((int *)dst)[i] = in_long(0x1F0);
-    }
+  waitdisk();
+  for (i = 0; i < SECTSIZE / 4; i ++) {
+    ((int *)dst)[i] = in_long(0x1F0);
+  }
 }
 
 void
 readseg(unsigned char *pa, int count, int offset) {
-    unsigned char *epa;
-    epa = pa + count;
-    pa -= offset % SECTSIZE;
-    offset = (offset / SECTSIZE) + 1;
-    for(; pa < epa; pa += SECTSIZE, offset ++)
-        readsect(pa, offset);
+  unsigned char *epa;
+  epa = pa + count;
+  pa -= offset % SECTSIZE;
+  offset = (offset / SECTSIZE) + 1;
+  for(; pa < epa; pa += SECTSIZE, offset ++)
+    readsect(pa, offset);
 }

am/arch/x86-qemu/img/boot/start.S

@@ -10,14 +10,14 @@ _start:
   movw    %ax, %ss
 
 # Set a 640 x 480 x 32 video mode
-  mov $0x4f01, %ax
-  mov $0x0112, %cx
-  mov $0x4000, %di
-  int $0x10
+  mov     $0x4f01, %ax
+  mov     $0x0112, %cx
+  mov     $0x4000, %di
+  int     $0x10
 
-  mov $0x4f02, %ax
-  mov $0x4112, %bx
-  int $0x10
+  mov     $0x4f02, %ax
+  mov     $0x4112, %bx
+  int     $0x10
 
   lgdt    gdtdesc
   movl    %cr0, %eax
@@ -32,9 +32,7 @@ start32:
   movw    %ax, %es
   movw    %ax, %ss
 
-  movl    (0x7020), %esp # multi-core hack
-                         # M[0x7020] is the core's bootstrap stack offset
-  addl    $0x2000, %esp
+  movl    $0x7000, %esp
   call    bootmain
 
 # GDT
@@ -46,4 +44,4 @@ gdt:
 
 gdtdesc:
   .word   (gdtdesc - gdt - 1)
-  .long   gdt
+  .long   gdt

am/arch/x86-qemu/src/mpe.c

@@ -5,15 +5,14 @@ static void (* volatile user_entry)();
 static intptr_t apboot_done = 0;
 
 static void mp_entry();
-
-static uint8_t cpu_stk[MAX_CPU][4096];
-static void call_switch_stk(void (*entry)());
+static void stack_switch(void (*entry)());
 
 int _mpe_init(void (*entry)()) {
   user_entry = entry;
-
-  call_switch_stk(mp_entry);
-  return 0; // never reaches here
+  stack_switch(mp_entry); // switch stack, and the bootstrap stack at
+                          // 0x7000 can be reused by an ap's bootloader
+  panic("mp_init should not return");
+  return 1;
 }
 
 int _cpu(void) {
@@ -26,12 +25,17 @@ int _ncpu() {
 
 intptr_t _atomic_xchg(volatile intptr_t *addr, intptr_t newval) {
   intptr_t result;
-  asm volatile("lock; xchgl %0, %1":
+  asm volatile("lock xchgl %0, %1":
     "+m"(*addr), "=a"(result): "1"(newval): "cc");
   return result;
 }
 
-void ap_init() {
+struct boot_info {
+  int is_ap;
+  void (*entry)();
+};
+
+static void ap_entry() {
   cpu_initgdt();
   lapic_init();
   ioapic_enable(IRQ_KBD, _cpu());
@@ -40,27 +44,26 @@ void ap_init() {
   user_entry();
 }
 
-#include <klib.h>
+static void stack_switch(void (*entry)()) {
+  static uint8_t cpu_stk[MAX_CPU][4096]; // each cpu gets a 4KB stack
+  asm volatile(
+    "movl %0, %%esp;"
+    "call *%1" : : "r"(&cpu_stk[_cpu() + 1][0]), "r"(entry));
+}
 
-static void mp_entry() {
+static void mp_entry() { // all cpus execute mp_entry()
   if (_cpu() != 0) {
-    call_switch_stk(ap_init);
+    // init an ap
+    stack_switch(ap_entry);
   } else {
+    // stack already swithced, boot all aps
+    volatile struct boot_info *boot = (void *)0x7000;
     for (int cpu = 1; cpu < ncpu; cpu ++) {
-      *(uint16_t*)(0x7c00 + 510) = 0x55aa;
-      *(uint32_t*)(0x7000) = 0x007c00ea;  // code for ljmp
-      *(uint32_t*)(0x7004) = 0x00000000;
-      *(void**)(0x7010) = (void*)mp_entry;
-      *(uint32_t*)(0x7020) = 0x4000; // 1KB bootstrap stack
-      lapic_bootap(cpu, 0x7000);
+      boot->is_ap = 1;
+      boot->entry = mp_entry;
+      lapic_bootap(cpu, 0x7c00);
       while (_atomic_xchg(&apboot_done, 0) != 1);
     }
     user_entry();
   }
 }
-
-static void call_switch_stk(void (*entry)()) {
-  asm volatile (
-    "movl %0, %%esp;"
-    "call *%1" : : "r"(&cpu_stk[_cpu() + 1][0]), "r"(entry));
-}