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Annotation of 3BSD/cmd/lisp/vfork.s, revision 1.1.1.1

1.1       root        1: # C library -- vfork
                      2: 
                      3: # pid = vfork();
                      4: #
                      5: # r1 == 0 in parent process, r1 == 1 in child process.
                      6: # r0 == pid of child in parent, r0 == pid of parent in child.
                      7: #
                      8: # trickery here, due to keith sklower, uses ret to clear the stack,
                      9: # and then returns with a jump indirect, since only one person can return
                     10: # with a ret off this stack... we do the ret before we vfork!
                     11: # 
                     12: 
                     13:        .set    vfork,66
                     14: .globl _fork
                     15: 
                     16: _fork:
                     17:        .word   0x0000
                     18:        movl    16(fp),r2
                     19:        movab   here,16(fp)
                     20:        ret
                     21: here:
                     22:        chmk    $vfork
                     23:        tstl    r1              # child process ?
                     24:        bneq    child   # yes
                     25:        bcc     parent          # if c-bit not set, fork ok
                     26: .globl _errno
                     27:        movl    r0,_errno
                     28:        mnegl   $1,r0
                     29:        jmp     (r2)
                     30: child:
                     31:        clrl    r0
                     32: parent:
                     33:        jmp     (r2)

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