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Diffstat (limited to 'i386/pc/rv86/rv86_real_int.c')
| -rw-r--r-- | i386/pc/rv86/rv86_real_int.c | 276 |
1 files changed, 0 insertions, 276 deletions
diff --git a/i386/pc/rv86/rv86_real_int.c b/i386/pc/rv86/rv86_real_int.c deleted file mode 100644 index d9c35b6..0000000 --- a/i386/pc/rv86/rv86_real_int.c +++ /dev/null @@ -1,276 +0,0 @@ -/* - * Copyright (c) 1995-1994 The University of Utah and - * the Computer Systems Laboratory at the University of Utah (CSL). - * All rights reserved. - * - * Permission to use, copy, modify and distribute this software is hereby - * granted provided that (1) source code retains these copyright, permission, - * and disclaimer notices, and (2) redistributions including binaries - * reproduce the notices in supporting documentation, and (3) all advertising - * materials mentioning features or use of this software display the following - * acknowledgement: ``This product includes software developed by the - * Computer Systems Laboratory at the University of Utah.'' - * - * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS - * IS" CONDITION. THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF - * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE. - * - * CSL requests users of this software to return to csl-dist@cs.utah.edu any - * improvements that they make and grant CSL redistribution rights. - * - * Author: Bryan Ford, University of Utah CSL - */ - -#include <mach/machine/seg.h> -#include <mach/machine/proc_reg.h> -#include <mach/machine/far_ptr.h> -#include <mach/machine/eflags.h> - -#include "vm_param.h" -#include "real.h" -#include "real_tss.h" -#include "cpu.h" -#include "debug.h" - - -/* - - There seem to be three main ways to handle v86 mode: - - * The v86 environment is just an extension of the normal kernel environment: - you can switch to and from v86 mode just as you can change any other processor state. - You always keep running on the separate "logical" stack, - which is the kernel stack when running in protected mode, - or the user stack when running in v86 mode. - When in v86 mode, the "actual" kernel stack is just a stub - big enough to switch back to the "normal" kernel stack, - which was being used as the user stack while running in v86 mode. - Thus, v86 and protected-mode "segments" of stack data - can be interleaved together on the same logical stack. - - - To make a real int call from kernel pmode, - switch to v86 mode and execute an int instruction, - then switch back to protected mode. - - - To reflect an interrupt to v86 mode: - - > If the processor was running in v86 mode, - just adjust the kernel and user stacks - to emulate a real-mode interrupt, and return. - - > If the processor was running in pmode, - switch to v86 mode and re-trigger the interrupt - with a software int instruction. - - - To handle an interrupt in pmode: - - > If the processor was running in v86 mode, - switch from the stub stack to the user stack that was in use - (could be different from the stack we set originally, - because BIOS/DOS code might have switched stacks!), - call the interrupt handler, switch back, and return. - - > If the processor was running in pmode, - just call the interrupt handler and return. - - This method only works if the whole "kernel" is <64KB - and generally compatible with real-mode execution. - This is the model my DOS extender currently uses. - - One major disadvantage of this method - is that interrupt handlers can't run "general" protected-mode code, - such as typical code compiled by GCC. - This is because, if an interrupt occurs while in v86 mode, - the v86-mode ss:sp may point basically anywhere in the low 1MB, - and it therefore it can't be used directly as a pmode stack; - and the only other stack available is the miniscule stub stack. - Since "general" protected-mode code expects a full-size stack - with an SS equal to the normal protected-mode DS, - neither of these available stacks will suffice. - It is impossible to switch back to the original kernel stack - because arbitrary DOS or BIOS code might have switched from it - to a different stack somewhere else in the low 1MB, - and we have no way of telling where the SP was when that happened. - The upshot is that interrupt handlers must be extremely simple; - in MOSS, all they do is post a signal to "the process," - and return immediately without actually handling the interrupt. - - * The v86 environment is a separate "task" with its own user and kernel stacks; - you switch back and forth as if between multiple ordinary tasks, - the tasks can preempt each other, go idle waiting for events, etc. - - - To make a real int call from kernel pmode, - the task making the call essentially does a synchronous IPC to the v86 task. - If the v86 task is busy with another request or a reflected interrupt, - the calling task will go idle until the v86 task is available. - - - Reflecting an interrupt to v86 mode - basically amounts to sending a Unix-like "signal" to the v86 task: - - > If the processor was running in the v86 task, - just adjust the kernel and user stacks - to emulate a real-mode interrupt, and return. - - > If the processor was running in a protected-mode task - (or another v86-mode task), - post a signal to the v86 task, wake it up if it's asleep, - and invoke the scheduler to switch to the v86 task - if it has a higher priority than the currently running task. - - - To handle an interrupt in pmode, - just call the interrupt handler and return. - It doesn't matter whether the interrupt was from v86 or pmode, - because the kernel stacks look the same in either case. - - One big problem with this method is that if interrupts are to be handled in v86 mode, - all the typical problems of handling interrupts in user-mode tasks pop up. - In particular, an interrupt can now cause preemption, - so this will break an interruptible but nonpreemptible environment. - (The problem is not that the interrupted task is "preempted" - to switch temporarily to the v86 task to handle the interrupt; - the problem is that when the v86 task is done handling the interrupt, - the scheduler will be invoked and some task other than the interrupted task may be run.) - - Of course, this is undoubtedly the right solution - if that's the interrupt model the OS is using anyway - (i.e. if the OS already supports user-level protected-mode interrupts). - - * A bastardization of the two above approaches: - treat the v86 environment as a separate "task", - but a special one that doesn't behave at all like other tasks. - The v86 "task" in this case is more of an "interrupt co-stack" - that grows and shrinks alongside the normal interrupt stack - (or the current kernel stack, if interrupts are handled on the kernel stack). - Interrupts and real calls can cause switches between these two interrupt stacks, - but they can't cause preemption in the normal sense. - The route taken while building the stacks is exactly the opposite - the route taken while tearing it down. - - Now two "kernel stack pointers" have to be maintained all the time instead of one. - When running in protected mode: - - - The ESP register contains the pmode stack pointer. - - Some global variable contains the v86 stack pointer. - - When running in v86 mode: - - - The ESP register contains the v86 stack pointer. - (Note that BIOS/DOS code can switch stacks, - so at any given time it may point practically anywhere!) - - The current tss's esp0 contains the pmode stack pointer. - - Whenever a switch is made, a stack frame is placed on the new co-stack - indicating that the switch was performed. - - - To make a real int call from kernel pmode, - build a real-mode interrupt stack frame on the v86 interrupt stack, - build a v86-mode trap stack frame on the pmode stack, - set the tss's esp0 to point to the end of that stack frame, - and iret from it. - Then when the magic "done-with-real-call" int instruction is hit, - the pmode interrupt handler will see it - and know to simply destroy the v86 trap stack on the pmode stack. - - - Handling an interrupt can always be thought of as going "through" pmode: - switching from the v86 stack to the pmode stack - if the processor was in v86 mode when the interrupt was taken, - and switching from the pmode stack back to the v86 stack as described above - if the interrupt is to be reflected to v86 mode. - - Of course, optimized paths are possible: - - - To reflect an interrupt to v86 mode: - - > If the processor was running in v86 mode, - just adjust the kernel and user stack frames and return. - - > If the processor was running in pmode, - do as described above for explicit real int calls. - - - To handle an interrupt in pmode: - - > If the processor was running in v86 mode, - switch to the pmode stack, - stash the old v86 stack pointer variable on the pmode stack, - and set the v86 stack pointer variable to the new location. - Call the interrupt handler, - then tear down everything and return to v86 mode. - - Observation: - In the first and third models, - explicit real int calls are entirely symmetrical - to hardware interrupts from pmode to v86 mode. - This is valid because of the interruptible but nonpreemptible model: - no scheduling is involved, and the stack(s) will always be torn down - in exactly the opposite order in which they were built up. - In the second model, - explicit real calls are quite different, - because the BIOS is interruptible but nonpreemptible: - you can reflect an interrupt into the v86 task at any time, - but you can only make an explicit request to that task when it's ready - (i.e. no other requests or interrupts are outstanding). - -*/ - - - -#define RV86_USTACK_SIZE 1024 - -vm_offset_t rv86_ustack_pa; -vm_offset_t rv86_return_int_pa; -struct far_pointer_32 rv86_usp; -struct far_pointer_16 rv86_rp; - -void rv86_real_int(int intnum, struct real_call_data *rcd) -{ - unsigned short old_tr; - unsigned int old_eflags; - - /* If this is the first time this routine is being called, - initialize the kernel stack. */ - if (!rv86_ustack_pa) - { - rv86_ustack_pa = 0xa0000 - RV86_USTACK_SIZE; /* XXX */ - - assert(rv86_ustack_pa < 0x100000); - - /* Use the top two bytes of the ustack for an 'int $0xff' instruction. */ - rv86_return_int_pa = rv86_ustack_pa + RV86_USTACK_SIZE - 2; - *(short*)phystokv(rv86_return_int_pa) = 0xffcd; - - /* Set up the v86 stack pointer. */ - rv86_usp.seg = rv86_rp.seg = rv86_ustack_pa >> 4; - rv86_usp.ofs = rv86_rp.ofs = (rv86_ustack_pa & 0xf) + RV86_USTACK_SIZE - 2; - - /* Pre-allocate a real-mode interrupt stack frame. */ - rv86_usp.ofs -= 6; - } - - /* Make sure interrupts are disabled. */ - old_eflags = get_eflags(); - - /* Switch to the TSS to use in v86 mode. */ - old_tr = get_tr(); - cpu[0].tables.gdt[REAL_TSS_IDX].access &= ~ACC_TSS_BUSY; - set_tr(REAL_TSS); - - asm volatile(" - pushl %%ebp - pushl %%eax - call rv86_real_int_asm - popl %%eax - popl %%ebp - " : - : "a" (rcd), "S" (intnum) - : "eax", "ebx", "ecx", "edx", "esi", "edi"); - - /* Switch to the original TSS. */ - cpu[0].tables.gdt[old_tr/8].access &= ~ACC_TSS_BUSY; - set_tr(old_tr); - - /* Restore the original processor flags. */ - set_eflags(old_eflags); -} - -void (*real_int)(int intnum, struct real_call_data *rcd) = rv86_real_int; - |