forked from Qortal/Brooklyn
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
113 lines
3.9 KiB
113 lines
3.9 KiB
/* SPDX-License-Identifier: GPL-2.0-or-later */ |
|
/* |
|
NetWinder Floating Point Emulator |
|
(c) Rebel.COM, 1998 |
|
(c) 1998, 1999 Philip Blundell |
|
|
|
Direct questions, comments to Scott Bambrough <scottb@netwinder.org> |
|
|
|
*/ |
|
#include <asm/assembler.h> |
|
#include <asm/opcodes.h> |
|
|
|
/* 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. */ |
|
|
|
#include <asm/asm-offsets.h> |
|
|
|
.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, #S_PC] @ get contents of PC; |
|
mov r6, r0 @ save the opcode |
|
emulate: |
|
ldr r1, [sp, #S_PSR] @ fetch the PSR |
|
bl arm_check_condition @ check the condition |
|
cmp r0, #ARM_OPCODE_CONDTEST_PASS @ condition passed? |
|
|
|
@ if condition code failed to match, next insn |
|
bne next @ get the next instruction; |
|
|
|
mov r0, r6 @ prepare for EmulateAll() |
|
bl EmulateAll @ emulate the instruction |
|
cmp r0, #0 @ was emulation successful |
|
reteq r4 @ no, return failure |
|
|
|
next: |
|
uaccess_enable r3 |
|
.Lx1: ldrt r6, [r5], #4 @ get the next instruction and |
|
@ increment PC |
|
uaccess_disable r3 |
|
and r2, r6, #0x0F000000 @ test for FP insns |
|
teq r2, #0x0C000000 |
|
teqne r2, #0x0D000000 |
|
teqne r2, #0x0E000000 |
|
retne r9 @ return ok if not a fp insn |
|
|
|
str r5, [sp, #S_PC] @ update PC copy in regs |
|
|
|
mov r0, r6 @ save a copy |
|
b emulate @ check condition and emulate |
|
|
|
@ 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. |
|
.pushsection .text.fixup,"ax" |
|
.align 2 |
|
.Lfix: ret r9 @ let the user eat segfaults |
|
.popsection |
|
|
|
.pushsection __ex_table,"a" |
|
.align 3 |
|
.long .Lx1, .Lfix |
|
.popsection
|
|
|