linux/arch/arm26/nwfpe/entry.S

/*
    NetWinder Floating Point Emulator
    (c) Rebel.COM, 1998
    (c) Philip Blundell 1998-1999

    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.
*/

#include <asm/asm-offsets.h>

/* This is the kernel's entry point into the floating point emulator.
It is called from the kernel with code similar to this:

	mov	fp, #0
	teqp	pc, #PSR_I_BIT | MODE_SVC
	ldr	r4, .LC2
	ldr	pc, [r4]		@ Call FP module USR entry point

The kernel expects the emulator to return via one of two possible
points of return it passes to the emulator.  The emulator, if
successful in its emulation, jumps to ret_from_exception and the
kernel takes care of returning control from the trap to the user code.
If the emulator is unable to emulate the instruction, it returns to
fpundefinstr and the kernel halts the user program with a core dump.

This routine does four things:

1) It saves SP into a variable called userRegisters.  The kernel has
created a struct pt_regs on the stack and saved the user registers
into it.  See /usr/include/asm/proc/ptrace.h for details.  The
emulator code uses userRegisters as the base of an array of words from
which the contents of the registers can be extracted.

2) It locates the FP emulator work area within the TSS structure and
points `fpa11' to it.

3) It calls EmulateAll to emulate a floating point instruction.
EmulateAll returns 1 if the emulation was successful, or 0 if not.

4) If an instruction has been emulated successfully, it looks ahead at
the next instruction.  If it is a floating point instruction, it
executes the instruction, without returning to user space.  In this
way it repeatedly looks ahead and executes floating point instructions
until it encounters a non floating point instruction, at which time it
returns via _fpreturn.

This is done to reduce the effect of the trap overhead on each
floating point instructions.  GCC attempts to group floating point
instructions to allow the emulator to spread the cost of the trap over
several floating point instructions.  */

	.globl	nwfpe_enter
nwfpe_enter:
	mov	sl, sp
	bl	FPA11_CheckInit		@ check to see if we are initialised

	ldr	r5, [sp, #60]		@ get contents of PC
	bic	r5, r5, #0xfc000003
	ldr	r0, [r5, #-4]		@ get actual instruction into r0
	bl	EmulateAll		@ emulate the instruction
1:	cmp	r0, #0			@ was emulation successful
	beq	fpundefinstr		@ no, return failure

next:
.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
	bne	ret_from_exception	@ return ok if not a fp insn

	ldr	r9, [sp, #60]		@ get new condition codes
	and	r9, r9, #0xfc000003
	orr	r7, r5, r9
	str	r7, [sp, #60]		@ update PC copy in regs

	mov	r0, r6			@ save a copy
	mov	r1, r9			@ 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()
	adr	lr, 1b
	orr	lr, lr, #3
	b	EmulateAll		@ if r0 != 0, goto EmulateAll

.Lret:	b	ret_from_exception	@ let the user eat segfaults
	
	@ We need to be prepared for the instruction at .Lx1 to fault.
	@ Emit the appropriate exception gunk to fix things up.
	.section __ex_table,"a"
	.align	3
	.long	.Lx1
	ldr	lr, [lr, $(.Lret - .Lx1)/4]
	.previous