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Diffstat (limited to 'arch/arm/nwfpe/entry.S')
-rw-r--r-- | arch/arm/nwfpe/entry.S | 119 |
1 files changed, 119 insertions, 0 deletions
diff --git a/arch/arm/nwfpe/entry.S b/arch/arm/nwfpe/entry.S new file mode 100644 index 000000000000..1dc13bc6d810 --- /dev/null +++ b/arch/arm/nwfpe/entry.S | |||
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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 | ||