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Diffstat (limited to 'arch/arm/nwfpe/entry26.S')
| -rw-r--r-- | arch/arm/nwfpe/entry26.S | 112 |
1 files changed, 112 insertions, 0 deletions
diff --git a/arch/arm/nwfpe/entry26.S b/arch/arm/nwfpe/entry26.S new file mode 100644 index 0000000..0ed38b0 --- /dev/null +++ b/arch/arm/nwfpe/entry26.S @@ -0,0 +1,112 @@ +/* + NetWinder Floating Point Emulator + (c) Rebel.COM, 1998 + (c) Philip Blundell 1998-1999 + + 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. +*/ + +#include <asm/constants.h> + +/* This is the kernel's entry point into the floating point emulator. +It is called from the kernel with code similar to this: + + mov fp, #0 + teqp pc, #PSR_I_BIT | MODE_SVC + ldr r4, .LC2 + ldr pc, [r4] @ Call FP module USR 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 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 to +fpundefinstr and the kernel halts the user program with a core dump. + +This routine does four things: + +1) It saves SP into a variable called userRegisters. 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. The +emulator code uses userRegisters as the base of an array of words from +which the contents of the registers can be extracted. + +2) It locates the FP emulator work area within the TSS structure and +points `fpa11' to it. + +3) It calls EmulateAll to emulate a floating point instruction. +EmulateAll returns 1 if the emulation was successful, or 0 if not. + +4) 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 sl, sp + ldr r5, [sp, #60] @ get contents of PC + bic r5, r5, #0xfc000003 + ldr r0, [r5, #-4] @ get actual instruction into r0 + bl EmulateAll @ emulate the instruction +1: cmp r0, #0 @ was emulation successful + beq fpundefinstr @ 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 + bne ret_from_exception @ return ok if not a fp insn + + ldr r9, [sp, #60] @ get new condition codes + and r9, r9, #0xfc000003 + orr r7, r5, r9 + str r7, [sp, #60] @ update PC copy in regs + + mov r0, r6 @ save a copy + mov r1, r9 @ 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() + adr lr, 1b + orr lr, lr, #3 + b EmulateAll @ if r0 != 0, goto EmulateAll + +.Lret: b ret_from_exception @ let the user eat segfaults + + @ We need to be prepared for the instruction at .Lx1 to fault. + @ Emit the appropriate exception gunk to fix things up. + .section __ex_table,"a" + .align 3 + .long .Lx1 + ldr lr, [lr, $(.Lret - .Lx1)/4] + .previous |