120 lines
4.3 KiB
ArmAsm
120 lines
4.3 KiB
ArmAsm
|
/*
|
||
|
|
NetWinder Floating Point Emulator
|
||
|
|
(c) Rebel.COM, 1998
|
||
|
|
(c) 1998, 1999 Philip Blundell
|
||
|
|
|
||
|
|
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.
|
||
|
|
*/
|
||
|
|
|
||
|
|
/* This is the kernel's entry point into the floating point emulator.
|
||
|
|
It is called from the kernel with code similar to this:
|
||
|
|
|
||
|
|
sub r4, r5, #4
|
||
|
|
ldrt r0, [r4] @ r0 = instruction
|
||
|
|
adrsvc al, r9, ret_from_exception @ r9 = normal FP return
|
||
|
|
adrsvc al, lr, fpundefinstr @ lr = undefined instr return
|
||
|
|
|
||
|
|
get_current_task r10
|
||
|
|
mov r8, #1
|
||
|
|
strb r8, [r10, #TSK_USED_MATH] @ set current->used_math
|
||
|
|
add r10, r10, #TSS_FPESAVE @ r10 = workspace
|
||
|
|
ldr r4, .LC2
|
||
|
|
ldr pc, [r4] @ Call FP emulator 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 (passed in
|
||
|
|
r9) 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 via _fpundefinstr (passed via lr) and the kernel halts the
|
||
|
|
user program with a core dump.
|
||
|
|
|
||
|
|
On entry to the emulator r10 points to an area of private FP workspace
|
||
|
|
reserved in the thread structure for this process. This is where the
|
||
|
|
emulator saves its registers across calls. The first word of this area
|
||
|
|
is used as a flag to detect the first time a process uses floating point,
|
||
|
|
so that the emulator startup cost can be avoided for tasks that don't
|
||
|
|
want it.
|
||
|
|
|
||
|
|
This routine does three things:
|
||
|
|
|
||
|
|
1) 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.
|
||
|
|
|
||
|
|
2) It calls EmulateAll to emulate a floating point instruction.
|
||
|
|
EmulateAll returns 1 if the emulation was successful, or 0 if not.
|
||
|
|
|
||
|
|
3) 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 r4, lr @ save the failure-return addresses
|
||
|
|
mov sl, sp @ we access the registers via 'sl'
|
||
|
|
|
||
|
|
ldr r5, [sp, #60] @ get contents of PC;
|
||
|
|
emulate:
|
||
|
|
bl EmulateAll @ emulate the instruction
|
||
|
|
cmp r0, #0 @ was emulation successful
|
||
|
|
moveq pc, r4 @ 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
|
||
|
|
movne pc, r9 @ return ok if not a fp insn
|
||
|
|
|
||
|
|
str r5, [sp, #60] @ update PC copy in regs
|
||
|
|
|
||
|
|
mov r0, r6 @ save a copy
|
||
|
|
ldr r1, [sp, #64] @ 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()
|
||
|
|
b emulate @ if r0 != 0, goto EmulateAll
|
||
|
|
|
||
|
|
@ We need to be prepared for the instructions at .Lx1 and .Lx2
|
||
|
|
@ to fault. Emit the appropriate exception gunk to fix things up.
|
||
|
|
@ ??? For some reason, faults can happen at .Lx2 even with a
|
||
|
|
@ plain LDR instruction. Weird, but it seems harmless.
|
||
|
|
.section .fixup,"ax"
|
||
|
|
.align 2
|
||
|
|
.Lfix: mov pc, r9 @ let the user eat segfaults
|
||
|
|
.previous
|
||
|
|
|
||
|
|
.section __ex_table,"a"
|
||
|
|
.align 3
|
||
|
|
.long .Lx1, .Lfix
|
||
|
|
.previous
|