- next three pages from Hellwig

pages/e01-04

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+	bne	3f / no
+	asr	r2 / yes, it is a parent
+	cmpb	p.stat-1(r2),$3 / is the child of this dying process a
+		                / zombie
+	bne	2f / no
+	clrb	p.stat-1(r2) / yes, free the child process
+2:
+	asl	r2
+3: / search the process name table for the dying process's parent
+	cmp	p.pid-2(r2),r4 / found it?
+	bne	3f / no
+	mov	r2,r5 / yes, put index to p.pid table (parents
+		      / process # x2) in r5
+3:
+	cmp	r2,$nproc+nproc / has whole table been searched?
+	blt	1b / no, go back
+	mov	r5,r1 / yes, r1 now has parents process # x2
+	beq	2f / no parent has been found. The process just dies
+	asr	r1 / set up index to p.stat
+	movb	p.stat-1(r1),r2 / move status of parent to r2
+	beq	2f / if its been freed, 2f
+	cmp	r2,$3 / is parent a zombie?
+	beq	2f / yes, 2f
+	movb	u.uno,r3 / move dying process's number to r3
+	movb	$3,p.stat-1(r3) / make the process a zombie
+	cmp	r2,$2 / is the parent waiting for this child to die
+	bne	2f / yes, notify parent not to wait any more
+	decb	p.stat-1(r1) / awaken it by putting it (parent)
+	mov	$runq+4,r2 / on the runq
+	jsr	r0, putlu
+2: / the process dies
+	clrb	u.uno / put zero as the process number, so "swap" will
+	jsr	r0,swap / overwrite process with another process
+	0	/ and thereby kill it; halt?
+
+intract: / interrupt action
+	cmp	*(sp),$rti / are you in a clock interrupt?
+	bne	1f / no, 1f
+	cmp	(sp)+,(sp)+ / pop clock pointer
+1: / now in user area
+	mov	r1,-(sp) / save r1
+	mov	u.ttyp,r1 / pointer to tty buffer in control to r1
+	cmpb	6(r1),$177 / is the interrupt char equal to "del"
+	beq	1f / yes, 1f
+	clrb	6(r1) / no, clear the byte (must be a quit character)
+	mov	(sp)+,r1 / restore r1
+	clr	u.quit / clear quit flag
+	bis	$20,2(sp) / set trace for quit (sets t bit of ps-trace trap)
+	rti	          / return from interrupt
+1: / interrupt char = del
+	clrb	6(r1) / clear the interrupt byte in the buffer
+	mov	(sp)+,r1 / restore r1
+	cmp	u.intr,$core / should control be transferred to loc core?
+	blo	1f
+	jmp	*u.intr / user to do rti yes, transfer to loc core
+1:

pages/e01-05

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+	sys	1 / exit
+
+syswait: / wait for a process to die
+	movb	u.uno,r1 / put parents process number in r1
+	asl	r1 / x2 to get index into p.pid table
+	mov	p.pid-2(r1),r1 / get the name of this process
+	clr	r2
+	clr	r3 / initialize reg 3
+1:
+	add	$2,r2 / use r2 for index into p.ppid table / search table
+		      / of parent processes for this process name
+	cmp	p.ppid-2(r2),r1 / r2 will contain the childs process number
+	bne	3f / branch if no match of parent process name
+	inc	r3 / yes, a match, r3 indicates number of children
+	asr	r2 / r2/2 to get index to p.stat table
+	cmpb	p.stat-1(r2),$3 / is the child process a zombie?
+	bne	2f / no, skip it
+	clrb	p.stat-1(r2) / yes, free it
+	asl	r2 / r2x2 to get index into p.pid table
+	mov	p.pid-2(r2),*u.r0 / put childs process name in (u.r0)
+	br	sysret1 / return cause child is dead
+2:
+	asl	r2 / r2x2 to get index into p.ppid table
+3:
+	cmp	r2,$nproc+nproc / have all processes been checked?
+	blt	1b / no, continue search
+	tst	r3 / one gets here if there are no children or children
+		   / that are still active
+	beq	error1 / there are no children, error
+	movb	u.uno,r1 / there are children so put parent process number
+		         / in r1
+	incb	p.stat-1(r1) / it is waiting for other children to die
+	jsr	r0,swap / swap it out, because it's waiting
+	br	syswait / wait on next process
+
+error1:
+	jmp	error / see 'error' routine
+sysret1:
+	jmp	sysret / see 'sysret' routine
+
+sysfork: / create a new process
+	clr	r1
+1: / search p.stat table for unused process number
+	inc	r1
+	tstb	p.stat-1(r1) / is process active, unused, dead
+	beq	1f / it's unused so branch
+	cmp	r1,$nproc / all processes checked
+	blt	1b / no, branch back
+	add	$2,18.(sp) / add 2 to pc when trap occured, points
+		           / to old process return
+	br	error1 / no room for a new process
+1:
+	movb	u.uno,-(sp) / save parent process number
+	movb	r1,u.uno / set child process number to r1
+	incb	p.stat-1(r1) / set p.stat entry for child process to
+		             / active status

pages/e01-06

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+	mov	u.ttyp,r2 / put pointer to parent process' control tty
+		          / buffer in r2
+	beq	2f / branch, if no such tty assigned
+	clrb	6(r2) / clear interrupt character in tty buffer
+2:
+	mov	$runq+4,r2
+	jsr	r0,putlu / put child process on lowest priority run queue
+	asl	r1 / multiply r1 by 2 to get index into p.pid table
+	inc	mpid / increment m.pid; get a new process name
+	mov	mpid,p.pid-2(r1) / put new process name in child process'
+		                 / name slot
+	movb	(sp),r2 / put parent process number in r2
+	asl	r2 / multiply by 2 to get index into below tables
+	mov	p.pid-2(r2),r2 / get process name of parent process
+	mov	r2,p.ppid-2(r1) / put parent process name in parent
+		                / process slot for child
+	mov	r2,*u.r0 / put parent process name on stack at location
+		         / where r0 was saved
+	mov	$sysret1,-(sp) /
+	mov	sp,u.usp / contents of sp at the time when user is
+		         / swapped out
+	mov	$sstack,sp / point sp to swapping stack space
+	jsr	r0,wswap / put child process out on drum
+	jsr	r0,unpack / unpack user stack
+	mov	u.usp,sp / restore user stack pointer
+	tst	(sp)+ / bump stack pointer
+	movb	(sp)+,u.uno / put parent process number in u.uno
+	mov	mpid,*u.r0 / put child process name on stack where r0
+		           / was saved
+	add	$2,18.(sp) / add 2 to pc on stack; gives parent
+		           / process return
+	clr	r1
+1: / search u.fp list to find the files opened by the parent process
+	movb	u.fp(r1),r2 / get an open file for this process
+	beq	2f / file has not been opened by parent, so branch
+	asl	r2 / multiply by 8
+	asl	r2 / to get index into fsp table
+	asl	r2
+	incb	fsp-2(r2) / increment number of processes using file,
+		          / because child will now be using this file
+2:
+	inc	r1 / get next open file
+	cmp	r1,$10. / 10. files is the maximum number which can be
+		        / opened
+	blt	1b / check next entry
+	br	sysret1
+
+sysread:
+	jsr	r0,rw1 / get i-number of file to be read into r1
+	tst	r1 / negative i—number?
+	ble	error1 / yes, error 1 to read it should be positive
+	jsr	r0,readi / read data into core
+	br	1f
+
+syswrite:
+	jsr	r0,rw1 / get i-number in r1 of file to write