1/* SPDX-License-Identifier: GPL-2.0-or-later */
  2/*
  3    NetWinder Floating Point Emulator
  4    (c) Rebel.COM, 1998
  5    (c) 1998, 1999 Philip Blundell
  6
  7    Direct questions, comments to Scott Bambrough <scottb@netwinder.org>
  8
  9*/
 10#include <asm/assembler.h>
 11#include <asm/opcodes.h>
 12
 13/* This is the kernel's entry point into the floating point emulator.
 14It is called from the kernel with code similar to this:
 15
 16	sub	r4, r5, #4
 17	ldrt	r0, [r4]			@ r0  = instruction
 18	adrsvc	al, r9, ret_from_exception	@ r9  = normal FP return
 19	adrsvc	al, lr, fpundefinstr		@ lr  = undefined instr return
 20
 21	get_current_task r10
 22	mov	r8, #1
 23	strb	r8, [r10, #TSK_USED_MATH]	@ set current->used_math
 24	add	r10, r10, #TSS_FPESAVE		@ r10 = workspace
 25	ldr	r4, .LC2
 26	ldr	pc, [r4]			@ Call FP emulator entry point
 27
 28The kernel expects the emulator to return via one of two possible
 29points of return it passes to the emulator.  The emulator, if
 30successful in its emulation, jumps to ret_from_exception (passed in
 31r9) and the kernel takes care of returning control from the trap to
 32the user code.  If the emulator is unable to emulate the instruction,
 33it returns via _fpundefinstr (passed via lr) and the kernel halts the
 34user program with a core dump.
 35
 36On entry to the emulator r10 points to an area of private FP workspace
 37reserved in the thread structure for this process.  This is where the
 38emulator saves its registers across calls.  The first word of this area
 39is used as a flag to detect the first time a process uses floating point,
 40so that the emulator startup cost can be avoided for tasks that don't
 41want it.
 42
 43This routine does three things:
 44
 451) The kernel has created a struct pt_regs on the stack and saved the
 46user registers into it.  See /usr/include/asm/proc/ptrace.h for details.
 47
 482) It calls EmulateAll to emulate a floating point instruction.
 49EmulateAll returns 1 if the emulation was successful, or 0 if not.
 50
 513) If an instruction has been emulated successfully, it looks ahead at
 52the next instruction.  If it is a floating point instruction, it
 53executes the instruction, without returning to user space.  In this
 54way it repeatedly looks ahead and executes floating point instructions
 55until it encounters a non floating point instruction, at which time it
 56returns via _fpreturn.
 57
 58This is done to reduce the effect of the trap overhead on each
 59floating point instructions.  GCC attempts to group floating point
 60instructions to allow the emulator to spread the cost of the trap over
 61several floating point instructions.  */
 62
 63#include <asm/asm-offsets.h>
 64
 65	.globl	nwfpe_enter
 66nwfpe_enter:
 67	mov	r4, lr			@ save the failure-return addresses
 68	mov	sl, sp			@ we access the registers via 'sl'
 69
 70	ldr	r5, [sp, #S_PC]		@ get contents of PC;
 71	mov	r6, r0			@ save the opcode
 72emulate:
 73	ldr	r1, [sp, #S_PSR]	@ fetch the PSR
 74	bl	arm_check_condition	@ check the condition
 75	cmp	r0, #ARM_OPCODE_CONDTEST_PASS	@ condition passed?
 76
 77	@ if condition code failed to match, next insn
 78	bne	next			@ get the next instruction;
 79
 80	mov	r0, r6			@ prepare for EmulateAll()
 81	bl	EmulateAll		@ emulate the instruction
 82	cmp	r0, #0			@ was emulation successful
 83	reteq	r4			@ no, return failure
 84
 85next:
 86	uaccess_enable r3
 87.Lx1:	ldrt	r6, [r5], #4		@ get the next instruction and
 88					@ increment PC
 89	uaccess_disable r3
 90	and	r2, r6, #0x0F000000	@ test for FP insns
 91	teq	r2, #0x0C000000
 92	teqne	r2, #0x0D000000
 93	teqne	r2, #0x0E000000
 94	retne	r9			@ return ok if not a fp insn
 95
 96	str	r5, [sp, #S_PC]		@ update PC copy in regs
 97
 98	mov	r0, r6			@ save a copy
 99	b	emulate			@ check condition and emulate
100
101	@ We need to be prepared for the instructions at .Lx1 and .Lx2 
102	@ to fault.  Emit the appropriate exception gunk to fix things up.
103	@ ??? For some reason, faults can happen at .Lx2 even with a
104	@ plain LDR instruction.  Weird, but it seems harmless.
105	.pushsection .text.fixup,"ax"
106	.align	2
107.Lfix:	ret	r9			@ let the user eat segfaults
108	.popsection
109
110	.pushsection __ex_table,"a"
111	.align	3
112	.long	.Lx1, .Lfix
113	.popsection