求看過(guò)4.4bsd代碼的大蝦指點(diǎn)

yizhengming

下面代碼來(lái)自4.4BSD-Lite2/usr/src/sys/hp300/hp300/locore.s
百思不得其解 a1 ＋ (sp - kstack ) 代表什么地址？

1. ENTRY(savectx)
   
2.     movl    sp@(4),a1
   
3.     movw    sr,a1@(PCB_PS)
   
4.     movl    usp,a0          | grab USP
   
5.     movl    a0,a1@(PCB_USP)     | and save it
   
6.     moveml  #0xFCFC,a1@(PCB_REGS)   | save non-scratch registers
   
7. 
   
8.     tstl    sp@(8)          | altreturn?
   
9.     jeq Lsavedone
   
10.     movl    sp,d0           | relocate current sp relative to a1
    
11.     subl    #_kstack,d0     |   (sp is relative to kstack):
    
12.     addl    d0,a1           |   a1 += sp - kstack
    
13.    movl    sp@,a1@         | write return pc at (relocated) sp@
    
14. Lsavedone:
    
15.     moveq   #0,d0           | return 0
    
16.     rts  
    

復(fù)制代碼

pitonas

no  看過(guò)  

yizhengming

換句話說(shuō)  我想知道內(nèi)核棧位于哪個(gè)位置，它和user里的pcb的聯(lián)系

gvim

回復(fù) 1# yizhengming

要看接近原始4.4BSD的就看看freebsd1 或者netbsd1 吧，4.4的好像體系都太難找，hp300。。。

gvim

回復(fù) 3# yizhengming


    棧是運(yùn)行期結(jié)構(gòu)，pcb是一堆數(shù)據(jù)描述一個(gè)進(jìn)程，出入棧信息可以放在pcb里面。

yizhengming

回復(fù) 6# gvim


    謝謝了   這個(gè)內(nèi)核棧的位置搞清楚了   還有個(gè)疑點(diǎn) sp(內(nèi)核堆棧指針) － kstack  代表什么？


cpu_fork(p1, p2)
    register struct proc *p1, *p2;
{
    register struct user *up = p2->p_addr;
    int offset;
    extern caddr_t getsp();
    extern char kstack[];

    p2->p_md.md_regs = p1->p_md.md_regs;
    p2->p_md.md_flags = (p1->p_md.md_flags & ~(MDP_AST|MDP_HPUXTRACE));

    /*  
     * Copy pcb and stack from proc p1 to p2.
     * We do this as cheaply as possible, copying only the active
     * part of the stack.  The stack and pcb need to agree;
     * this is tricky, as the final pcb is constructed by savectx,
     * but its frame isn't yet on the stack when the stack is copied.
     * switch compensates for this when the child eventually runs.
     * This should be done differently, with a single call
     * that copies and updates the pcb+stack,
     * replacing the bcopy and savectx.
     */
    p2->p_addr->u_pcb = p1->p_addr->u_pcb;
    offset = getsp() - kstack;
    bcopy((caddr_t)kstack + offset, (caddr_t)p2->p_addr + offset,
        (unsigned) ctob(UPAGES) - offset);

    PMAP_ACTIVATE(&p2->p_vmspace->vm_pmap, &up->u_pcb, 0);

    /*  
     * Arrange for a non-local goto when the new process
     * is started, to resume here, returning nonzero from setjmp.
     */
    if (savectx(up, 1)) {
        /*
         * Return 1 in child.
         */
        return (1);
    }
    return (0);
}

gvim

回復(fù) 7# yizhengming


    體系太偏了，不理解就不好說(shuō)。