main.c

#include "types.h"
#include "defs.h"
#include "param.h"
#include "memlayout.h"
#include "mmu.h"
#include "proc.h"
#include "x86.h"

static void startothers(void);

static void mpmain(void)  __attribute__((noreturn));

extern pde_t *kpgdir;
extern char end[]; // first address after kernel loaded from ELF file

// Bootstrap processor starts running C code here.
// Allocate a real stack and switch to it, first
// doing some setup required for memory allocator to work.
int
main(void) {
    kinit1(end, P2V(4 * 1024 * 1024)); // phys page allocator
    kvmalloc();      // kernel page table
    mpinit();        // collect info about this machine
    lapicinit();
    seginit();       // set up segments
    cprintf("\ncpu%d: starting xv6\n\n", cpu->id);
    picinit();       // interrupt controller
    ioapicinit();    // another interrupt controller
    consoleinit();   // I/O devices & their interrupts
    uartinit();      // serial port
    pinit();         // process table
    tvinit();        // trap vectors
    binit();         // buffer cache
    fileinit();      // file table
    ideinit();       // disk
    if (!ismp)
        timerinit();   // uniprocessor timer
    startothers();   // start other processors
    kinit2(P2V(4 * 1024 * 1024), P2V(PHYSTOP)); // must come after startothers()
    userinit();      // first user process
    // Finish setting up this processor in mpmain.
    mpmain();
}

// Other CPUs jump here from entryother.S.
static void
mpenter(void) {
    switchkvm();
    seginit();
    lapicinit();
    mpmain();
}

// Common CPU setup code.
static void
mpmain(void) {
    cprintf("cpu%d: starting\n", cpu->id);
    idtinit();       // load idt register
    xchg(&cpu->started, 1); // tell startothers() we're up
    scheduler();     // start running processes
}

pde_t entrypgdir[];  // For entry.S

// Start the non-boot (AP) processors.
static void
startothers(void) {
    extern uchar _binary_entryother_start[], _binary_entryother_size[];
    uchar *code;
    struct cpu *c;
    char *stack;

    // Write entry code to unused memory at 0x7000.
    // The linker has placed the image of entryother.S in
    // _binary_entryother_start.
    code = p2v(0x7000);
    memmove(code, _binary_entryother_start, (uint) _binary_entryother_size);

    for (c = cpus; c < cpus + ncpu; c++) {
        if (c == cpus + cpunum())  // We've started already.
            continue;

        // Tell entryother.S what stack to use, where to enter, and what
        // pgdir to use. We cannot use kpgdir yet, because the AP processor
        // is running in low  memory, so we use entrypgdir for the APs too.
        stack = kalloc();
        *(void **) (code - 4) = stack + KSTACKSIZE;
        *(void **) (code - 8) = mpenter;
        *(int **) (code - 12) = (void *) v2p(entrypgdir);

        lapicstartap(c->id, v2p(code));

        // wait for cpu to finish mpmain()
        while (c->started == 0);
    }
}

// Boot page table used in entry.S and entryother.S.
// Page directories (and page tables), must start on a page boundary,
// hence the "__aligned__" attribute.  
// Use PTE_PS in page directory entry to enable 4Mbyte pages.
__attribute__((__aligned__(PGSIZE)))
pde_t entrypgdir[NPDENTRIES] = {
        // Map VA's [0, 4MB) to PA's [0, 4MB)
        [0] = (0) | PTE_P | PTE_W | PTE_PS,
        // Map VA's [KERNBASE, KERNBASE+4MB) to PA's [0, 4MB)
        [KERNBASE >> PDXSHIFT] = (0) | PTE_P | PTE_W | PTE_PS,
};

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