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+ 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
+ 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/constants.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
+ mov sl, sp
+ 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
+.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