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1da177e4 LT |
1 | /* |
2 | NetWinder Floating Point Emulator | |
3 | (c) Rebel.COM, 1998 | |
4 | (c) 1998, 1999 Philip Blundell | |
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 | /* This is the kernel's entry point into the floating point emulator. | |
24 | It is called from the kernel with code similar to this: | |
25 | ||
26 | sub r4, r5, #4 | |
27 | ldrt r0, [r4] @ r0 = instruction | |
28 | adrsvc al, r9, ret_from_exception @ r9 = normal FP return | |
29 | adrsvc al, lr, fpundefinstr @ lr = undefined instr return | |
30 | ||
31 | get_current_task r10 | |
32 | mov r8, #1 | |
33 | strb r8, [r10, #TSK_USED_MATH] @ set current->used_math | |
34 | add r10, r10, #TSS_FPESAVE @ r10 = workspace | |
35 | ldr r4, .LC2 | |
36 | ldr pc, [r4] @ Call FP emulator entry point | |
37 | ||
38 | The kernel expects the emulator to return via one of two possible | |
39 | points of return it passes to the emulator. The emulator, if | |
40 | successful in its emulation, jumps to ret_from_exception (passed in | |
41 | r9) and the kernel takes care of returning control from the trap to | |
42 | the user code. If the emulator is unable to emulate the instruction, | |
43 | it returns via _fpundefinstr (passed via lr) and the kernel halts the | |
44 | user program with a core dump. | |
45 | ||
46 | On entry to the emulator r10 points to an area of private FP workspace | |
47 | reserved in the thread structure for this process. This is where the | |
48 | emulator saves its registers across calls. The first word of this area | |
49 | is used as a flag to detect the first time a process uses floating point, | |
50 | so that the emulator startup cost can be avoided for tasks that don't | |
51 | want it. | |
52 | ||
53 | This routine does three things: | |
54 | ||
55 | 1) The kernel has created a struct pt_regs on the stack and saved the | |
56 | user registers into it. See /usr/include/asm/proc/ptrace.h for details. | |
57 | ||
58 | 2) It calls EmulateAll to emulate a floating point instruction. | |
59 | EmulateAll returns 1 if the emulation was successful, or 0 if not. | |
60 | ||
61 | 3) If an instruction has been emulated successfully, it looks ahead at | |
62 | the next instruction. If it is a floating point instruction, it | |
63 | executes the instruction, without returning to user space. In this | |
64 | way it repeatedly looks ahead and executes floating point instructions | |
65 | until it encounters a non floating point instruction, at which time it | |
66 | returns via _fpreturn. | |
67 | ||
68 | This is done to reduce the effect of the trap overhead on each | |
69 | floating point instructions. GCC attempts to group floating point | |
70 | instructions to allow the emulator to spread the cost of the trap over | |
71 | several floating point instructions. */ | |
72 | ||
73 | .globl nwfpe_enter | |
74 | nwfpe_enter: | |
75 | mov r4, lr @ save the failure-return addresses | |
76 | mov sl, sp @ we access the registers via 'sl' | |
77 | ||
78 | ldr r5, [sp, #60] @ get contents of PC; | |
79 | emulate: | |
80 | bl EmulateAll @ emulate the instruction | |
81 | cmp r0, #0 @ was emulation successful | |
82 | moveq pc, r4 @ no, return failure | |
83 | ||
84 | next: | |
85 | .Lx1: ldrt r6, [r5], #4 @ get the next instruction and | |
86 | @ increment PC | |
87 | ||
88 | and r2, r6, #0x0F000000 @ test for FP insns | |
89 | teq r2, #0x0C000000 | |
90 | teqne r2, #0x0D000000 | |
91 | teqne r2, #0x0E000000 | |
92 | movne pc, r9 @ return ok if not a fp insn | |
93 | ||
94 | str r5, [sp, #60] @ update PC copy in regs | |
95 | ||
96 | mov r0, r6 @ save a copy | |
97 | ldr r1, [sp, #64] @ fetch the condition codes | |
98 | bl checkCondition @ check the condition | |
99 | cmp r0, #0 @ r0 = 0 ==> condition failed | |
100 | ||
101 | @ if condition code failed to match, next insn | |
102 | beq next @ get the next instruction; | |
103 | ||
104 | mov r0, r6 @ prepare for EmulateAll() | |
105 | b emulate @ if r0 != 0, goto EmulateAll | |
106 | ||
107 | @ We need to be prepared for the instructions at .Lx1 and .Lx2 | |
108 | @ to fault. Emit the appropriate exception gunk to fix things up. | |
109 | @ ??? For some reason, faults can happen at .Lx2 even with a | |
110 | @ plain LDR instruction. Weird, but it seems harmless. | |
111 | .section .fixup,"ax" | |
112 | .align 2 | |
113 | .Lfix: mov pc, r9 @ let the user eat segfaults | |
114 | .previous | |
115 | ||
116 | .section __ex_table,"a" | |
117 | .align 3 | |
118 | .long .Lx1, .Lfix | |
119 | .previous |