1/* 2 NetWinder Floating Point Emulator 3 (c) Rebel.COM, 1998 4 (c) Philip Blundell 1998-1999 5 6 Direct questions, comments to Scott Bambrough <scottb@netwinder.org> 7 8 This program is free software; you can redistribute it and/or modify 9 it under the terms of the GNU General Public License as published by 10 the Free Software Foundation; either version 2 of the License, or 11 (at your option) any later version. 12 13 This program is distributed in the hope that it will be useful, 14 but WITHOUT ANY WARRANTY; without even the implied warranty of 15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 16 GNU General Public License for more details. 17 18 You should have received a copy of the GNU General Public License 19 along with this program; if not, write to the Free Software 20 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. 21*/ 22 23#include <asm/constants.h> 24 25/* This is the kernel's entry point into the floating point emulator. 26It is called from the kernel with code similar to this: 27 28 mov fp, #0 29 teqp pc, #I_BIT | MODE_SVC 30 ldr r4, .LC2 31 ldr pc, [r4] @ Call FP module USR entry point 32 33The kernel expects the emulator to return via one of two possible 34points of return it passes to the emulator. The emulator, if 35successful in its emulation, jumps to ret_from_exception and the 36kernel takes care of returning control from the trap to the user code. 37If the emulator is unable to emulate the instruction, it returns to 38fpundefinstr and the kernel halts the user program with a core dump. 39 40This routine does four things: 41 421) It saves SP into a variable called userRegisters. The kernel has 43created a struct pt_regs on the stack and saved the user registers 44into it. See /usr/include/asm/proc/ptrace.h for details. The 45emulator code uses userRegisters as the base of an array of words from 46which the contents of the registers can be extracted. 47 482) It locates the FP emulator work area within the TSS structure and 49points `fpa11' to it. 50 513) It calls EmulateAll to emulate a floating point instruction. 52EmulateAll returns 1 if the emulation was successful, or 0 if not. 53 544) If an instruction has been emulated successfully, it looks ahead at 55the next instruction. If it is a floating point instruction, it 56executes the instruction, without returning to user space. In this 57way it repeatedly looks ahead and executes floating point instructions 58until it encounters a non floating point instruction, at which time it 59returns via _fpreturn. 60 61This is done to reduce the effect of the trap overhead on each 62floating point instructions. GCC attempts to group floating point 63instructions to allow the emulator to spread the cost of the trap over 64several floating point instructions. */ 65 66 .globl nwfpe_enter 67nwfpe_enter: 68 mov sl, sp 69 ldr r5, [sp, #60] @ get contents of PC 70 bic r5, r5, #0xfc000003 71 ldr r0, [r5, #-4] @ get actual instruction into r0 72 bl EmulateAll @ emulate the instruction 731: cmp r0, #0 @ was emulation successful 74 beq fpundefinstr @ no, return failure 75 76next: 77.Lx1: ldrt r6, [r5], #4 @ get the next instruction and 78 @ increment PC 79 80 and r2, r6, #0x0F000000 @ test for FP insns 81 teq r2, #0x0C000000 82 teqne r2, #0x0D000000 83 teqne r2, #0x0E000000 84 bne ret_from_exception @ return ok if not a fp insn 85 86 ldr r9, [sp, #60] @ get new condition codes 87 and r9, r9, #0xfc000003 88 orr r7, r5, r9 89 str r7, [sp, #60] @ update PC copy in regs 90 91 mov r0, r6 @ save a copy 92 mov r1, r9 @ fetch the condition codes 93 bl checkCondition @ check the condition 94 cmp r0, #0 @ r0 = 0 ==> condition failed 95 96 @ if condition code failed to match, next insn 97 beq next @ get the next instruction; 98 99 mov r0, r6 @ prepare for EmulateAll() 100 adr lr, 1b 101 orr lr, lr, #3 102 b EmulateAll @ if r0 != 0, goto EmulateAll 103 104.Lret: b ret_from_exception @ let the user eat segfaults 105 106 @ We need to be prepared for the instruction at .Lx1 to fault. 107 @ Emit the appropriate exception gunk to fix things up. 108 .section __ex_table,"a" 109 .align 3 110 .long .Lx1 111 ldr lr, [lr, $(.Lret - .Lx1)/4] 112 .previous 113