Commit graph

8 commits

Author SHA1 Message Date
Frans Kaashoek 40889627ba Initial version of single-cpu xv6 with page tables 2010-07-02 14:51:53 -04:00
Russ Cox 2c5f7aba38 initproc, usegment, swtch tweaks 2009-07-11 19:28:29 -07:00
kolya c100d9ee2d cleaner swtch.S 2008-10-15 05:14:10 +00:00
rsc c95bde8163 yank out stack overflow checking ugliness 2007-09-27 20:38:53 +00:00
rsc 39c3fb1b15 overkill: use segments to catch stack overflow (delete before next year) 2007-09-27 19:39:10 +00:00
rsc 818fc0125e replace setjmp/longjmp with swtch 2007-08-28 12:48:33 +00:00
rsc 6b765c480f rename swtch.S to setjmp.S 2006-07-16 15:40:51 +00:00
rsc 5ce9751cab Changes to allow use of native x86 ELF compilers, which on my
Linux 2.4 box using gcc 3.4.6 don't seem to follow the same
conventions as the i386-jos-elf-gcc compilers.
Can run make 'TOOLPREFIX=' or edit the Makefile.

curproc[cpu()] can now be NULL, indicating that no proc is running.
This seemed safer to me than having curproc[0] and curproc[1]
both pointing at proc[0] potentially.

The old implementation of swtch depended on the stack frame layout
used inside swtch being okay to return from on the other stack
(exactly the V6 you are not expected to understand this).
It also could be called in two contexts: at boot time, to schedule
the very first process, and later, on behalf of a process, to sleep
or schedule some other process.

I split this into two functions: scheduler and swtch.

The scheduler is now a separate never-returning function, invoked
by each cpu once set up.  The scheduler looks like:

	scheduler() {
		setjmp(cpu.context);

		pick proc to schedule
		blah blah blah

		longjmp(proc.context)
	}

The new swtch is intended to be called only when curproc[cpu()] is not NULL,
that is, only on behalf of a user proc.  It does:

	swtch() {
		if(setjmp(proc.context) == 0)
			longjmp(cpu.context)
	}

to save the current proc context and then jump over to the scheduler,
running on the cpu stack.

Similarly the system call stubs are now in assembly in usys.S to avoid
needing to know the details of stack frame layout used by the compiler.

Also various changes in the debugging prints.
2006-07-11 01:07:40 +00:00