/*    NetWinder Floating Point Emulator    (c) Rebel.COM, 1998    (c) 1998, 1999 Philip Blundell    Direct questions, comments to Scott Bambrough <scottb@netwinder.org>    This program is free software; you can redistribute it and/or modify    it under the terms of the GNU General Public License as published by    the Free Software Foundation; either version 2 of the License, or    (at your option) any later version.    This program is distributed in the hope that it will be useful,    but WITHOUT ANY WARRANTY; without even the implied warranty of    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the    GNU General Public License for more details.    You should have received a copy of the GNU General Public License    along with this program; if not, write to the Free Software    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.*//* This is the kernel's entry point into the floating point emulator.It is called from the kernel with code similar to this:	sub	r4, r5, #4	ldrt	r0, [r4]			@ r0  = instruction	adrsvc	al, r9, ret_from_exception	@ r9  = normal FP return	adrsvc	al, lr, fpundefinstr		@ lr  = undefined instr return	get_current_task r10	mov	r8, #1	strb	r8, [r10, #TSK_USED_MATH]	@ set current->used_math	add	r10, r10, #TSS_FPESAVE		@ r10 = workspace	ldr	r4, .LC2	ldr	pc, [r4]			@ Call FP emulator entry pointThe kernel expects the emulator to return via one of two possiblepoints of return it passes to the emulator.  The emulator, ifsuccessful in its emulation, jumps to ret_from_exception (passed inr9) and the kernel takes care of returning control from the trap tothe user code.  If the emulator is unable to emulate the instruction,it returns via _fpundefinstr (passed via lr) and the kernel halts theuser program with a core dump.On entry to the emulator r10 points to an area of private FP workspacereserved in the thread structure for this process.  This is where theemulator saves its registers across calls.  The first word of this areais used as a flag to detect the first time a process uses floating point,so that the emulator startup cost can be avoided for tasks that don'twant it.This routine does three things:1) The kernel has created a struct pt_regs on the stack and saved theuser registers into it.  See /usr/include/asm/proc/ptrace.h for details.2) It calls EmulateAll to emulate a floating point instruction.EmulateAll returns 1 if the emulation was successful, or 0 if not.3) If an instruction has been emulated successfully, it looks ahead atthe next instruction.  If it is a floating point instruction, itexecutes the instruction, without returning to user space.  In thisway it repeatedly looks ahead and executes floating point instructionsuntil it encounters a non floating point instruction, at which time itreturns via _fpreturn.This is done to reduce the effect of the trap overhead on eachfloating point instructions.  GCC attempts to group floating pointinstructions to allow the emulator to spread the cost of the trap overseveral floating point instructions.  */	.globl	nwfpe_enternwfpe_enter:	mov	r4, lr			@ save the failure-return addresses	mov	sl, sp			@ we access the registers via 'sl'	ldr	r5, [sp, #60]		@ get contents of PC;emulate:	bl	EmulateAll		@ emulate the instruction	cmp	r0, #0			@ was emulation successful	moveq	pc, r4			@ no, return failurenext:.Lx1:	ldrt	r6, [r5], #4		@ get the next instruction and					@ increment PC	and	r2, r6, #0x0F000000	@ test for FP insns	teq	r2, #0x0C000000	teqne	r2, #0x0D000000	teqne	r2, #0x0E000000	movne	pc, r9			@ return ok if not a fp insn	str	r5, [sp, #60]		@ update PC copy in regs	mov	r0, r6			@ save a copy	ldr	r1, [sp, #64]		@ fetch the condition codes	bl	checkCondition		@ check the condition	cmp	r0, #0			@ r0 = 0 ==> condition failed	@ if condition code failed to match, next insn	beq	next			@ get the next instruction;	mov	r0, r6			@ prepare for EmulateAll()	b	emulate			@ if r0 != 0, goto EmulateAll	@ We need to be prepared for the instructions at .Lx1 and .Lx2 	@ to fault.  Emit the appropriate exception gunk to fix things up.	@ ??? For some reason, faults can happen at .Lx2 even with a	@ plain LDR instruction.  Weird, but it seems harmless.	.section .fixup,"ax"	.align	2.Lfix:	mov	pc, r9			@ let the user eat segfaults	.previous	.section __ex_table,"a"	.align	3	.long	.Lx1, .Lfix	.previous