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linux/arch/arc/kernel/entry.S
Vineet Gupta 98edfab4c1 ARC: add some more comments to ret_from_fork 
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
2015-02-02 17:08:37 +05:30

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/*
* Low Level Interrupts/Traps/Exceptions(non-TLB) Handling for ARC
*
* Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* vineetg: May 2011
* -Userspace unaligned access emulation
*
* vineetg: Feb 2011 (ptrace low level code fixes)
* -traced syscall return code (r0) was not saved into pt_regs for restoring
* into user reg-file when traded task rets to user space.
* -syscalls needing arch-wrappers (mainly for passing sp as pt_regs)
* were not invoking post-syscall trace hook (jumping directly into
* ret_from_system_call)
*
* vineetg: Nov 2010:
* -Vector table jumps (@8 bytes) converted into branches (@4 bytes)
* -To maintain the slot size of 8 bytes/vector, added nop, which is
* not executed at runtime.
*
* vineetg: Nov 2009 (Everything needed for TIF_RESTORE_SIGMASK)
* -do_signal()invoked upon TIF_RESTORE_SIGMASK as well
* -Wrappers for sys_{,rt_}sigsuspend() nolonger needed as they don't
* need ptregs anymore
*
* Vineetg: Oct 2009
* -In a rare scenario, Process gets a Priv-V exception and gets scheduled
* out. Since we don't do FAKE RTIE for Priv-V, CPU excpetion state remains
* active (AE bit enabled). This causes a double fault for a subseq valid
* exception. Thus FAKE RTIE needed in low level Priv-Violation handler.
* Instr Error could also cause similar scenario, so same there as well.
*
* Vineetg: March 2009 (Supporting 2 levels of Interrupts)
*
* Vineetg: Aug 28th 2008: Bug #94984
* -Zero Overhead Loop Context shd be cleared when entering IRQ/EXcp/Trap
* Normally CPU does this automatically, however when doing FAKE rtie,
* we need to explicitly do this. The problem in macros
* FAKE_RET_FROM_EXCPN and FAKE_RET_FROM_EXCPN_LOCK_IRQ was that this bit
* was being "CLEARED" rather then "SET". Since it is Loop INHIBIT Bit,
* setting it and not clearing it clears ZOL context
*
* Vineetg: May 16th, 2008
* - r25 now contains the Current Task when in kernel
*
* Vineetg: Dec 22, 2007
* Minor Surgery of Low Level ISR to make it SMP safe
* - MMU_SCRATCH0 Reg used for freeing up r9 in Level 1 ISR
* - _current_task is made an array of NR_CPUS
* - Access of _current_task wrapped inside a macro so that if hardware
* team agrees for a dedicated reg, no other code is touched
*
* Amit Bhor, Rahul Trivedi, Kanika Nema, Sameer Dhavale : Codito Tech 2004
*/
/*------------------------------------------------------------------
* Function ABI
*------------------------------------------------------------------
*
* Arguments r0 - r7
* Caller Saved Registers r0 - r12
* Callee Saved Registers r13- r25
* Global Pointer (gp) r26
* Frame Pointer (fp) r27
* Stack Pointer (sp) r28
* Interrupt link register (ilink1) r29
* Interrupt link register (ilink2) r30
* Branch link register (blink) r31
*------------------------------------------------------------------
*/
.cpu A7
;############################ Vector Table #################################
.macro VECTOR lbl
#if 1 /* Just in case, build breaks */
j \lbl
#else
b \lbl
nop
#endif
.endm
.section .vector, "ax",@progbits
.align 4
/* Each entry in the vector table must occupy 2 words. Since it is a jump
* across sections (.vector to .text) we are gauranteed that 'j somewhere'
* will use the 'j limm' form of the intrsuction as long as somewhere is in
* a section other than .vector.
*/
; ********* Critical System Events **********************
VECTOR res_service ; 0x0, Restart Vector (0x0)
VECTOR mem_service ; 0x8, Mem exception (0x1)
VECTOR instr_service ; 0x10, Instrn Error (0x2)
; ******************** Device ISRs **********************
#ifdef CONFIG_ARC_IRQ3_LV2
VECTOR handle_interrupt_level2
#else
VECTOR handle_interrupt_level1
#endif
VECTOR handle_interrupt_level1
#ifdef CONFIG_ARC_IRQ5_LV2
VECTOR handle_interrupt_level2
#else
VECTOR handle_interrupt_level1
#endif
#ifdef CONFIG_ARC_IRQ6_LV2
VECTOR handle_interrupt_level2
#else
VECTOR handle_interrupt_level1
#endif
.rept 25
VECTOR handle_interrupt_level1 ; Other devices
.endr
/* FOR ARC600: timer = 0x3, uart = 0x8, emac = 0x10 */
; ******************** Exceptions **********************
VECTOR EV_MachineCheck ; 0x100, Fatal Machine check (0x20)
VECTOR EV_TLBMissI ; 0x108, Intruction TLB miss (0x21)
VECTOR EV_TLBMissD ; 0x110, Data TLB miss (0x22)
VECTOR EV_TLBProtV ; 0x118, Protection Violation (0x23)
; or Misaligned Access
VECTOR EV_PrivilegeV ; 0x120, Privilege Violation (0x24)
VECTOR EV_Trap ; 0x128, Trap exception (0x25)
VECTOR EV_Extension ; 0x130, Extn Intruction Excp (0x26)
.rept 24
VECTOR reserved ; Reserved Exceptions
.endr
#include <linux/linkage.h> /* {EXTRY,EXIT} */
#include <asm/entry.h> /* SAVE_ALL_{INT1,INT2,SYS...} */
#include <asm/errno.h>
#include <asm/arcregs.h>
#include <asm/irqflags.h>
;##################### Scratch Mem for IRQ stack switching #############
ARCFP_DATA int1_saved_reg
.align 32
.type int1_saved_reg, @object
.size int1_saved_reg, 4
int1_saved_reg:
.zero 4
/* Each Interrupt level needs its own scratch */
#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
ARCFP_DATA int2_saved_reg
.type int2_saved_reg, @object
.size int2_saved_reg, 4
int2_saved_reg:
.zero 4
#endif
; ---------------------------------------------
.section .text, "ax",@progbits
res_service: ; processor restart
flag 0x1 ; not implemented
nop
nop
reserved: ; processor restart
rtie ; jump to processor initializations
;##################### Interrupt Handling ##############################
#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
; ---------------------------------------------
; Level 2 ISR: Can interrupt a Level 1 ISR
; ---------------------------------------------
ENTRY(handle_interrupt_level2)
; TODO-vineetg for SMP this wont work
; free up r9 as scratchpad
st r9, [@int2_saved_reg]
;Which mode (user/kernel) was the system in when intr occured
lr r9, [status32_l2]
SWITCH_TO_KERNEL_STK
SAVE_ALL_INT2
;------------------------------------------------------
; if L2 IRQ interrupted a L1 ISR, disable preemption
;------------------------------------------------------
ld r9, [sp, PT_status32] ; get statu32_l2 (saved in pt_regs)
bbit0 r9, STATUS_A1_BIT, 1f ; L1 not active when L2 IRQ, so normal
; A1 is set in status32_l2
; bump thread_info->preempt_count (Disable preemption)
GET_CURR_THR_INFO_FROM_SP r10
ld r9, [r10, THREAD_INFO_PREEMPT_COUNT]
add r9, r9, 1
st r9, [r10, THREAD_INFO_PREEMPT_COUNT]
1:
;------------------------------------------------------
; setup params for Linux common ISR and invoke it
;------------------------------------------------------
lr r0, [icause2]
and r0, r0, 0x1f
bl.d @arch_do_IRQ
mov r1, sp
mov r8,0x2
sr r8, [AUX_IRQ_LV12] ; clear bit in Sticky Status Reg
b ret_from_exception
END(handle_interrupt_level2)
#endif
; ---------------------------------------------
; Level 1 ISR
; ---------------------------------------------
ENTRY(handle_interrupt_level1)
/* free up r9 as scratchpad */
#ifdef CONFIG_SMP
sr r9, [ARC_REG_SCRATCH_DATA0]
#else
st r9, [@int1_saved_reg]
#endif
;Which mode (user/kernel) was the system in when intr occured
lr r9, [status32_l1]
SWITCH_TO_KERNEL_STK
SAVE_ALL_INT1
lr r0, [icause1]
and r0, r0, 0x1f
#ifdef CONFIG_TRACE_IRQFLAGS
; icause1 needs to be read early, before calling tracing, which
; can clobber scratch regs, hence use of stack to stash it
push r0
TRACE_ASM_IRQ_DISABLE
pop r0
#endif
bl.d @arch_do_IRQ
mov r1, sp
mov r8,0x1
sr r8, [AUX_IRQ_LV12] ; clear bit in Sticky Status Reg
b ret_from_exception
END(handle_interrupt_level1)
;################### Non TLB Exception Handling #############################
; ---------------------------------------------
; Instruction Error Exception Handler
; ---------------------------------------------
ENTRY(instr_service)
EXCEPTION_PROLOGUE
lr r0, [efa]
mov r1, sp
FAKE_RET_FROM_EXCPN r9
bl do_insterror_or_kprobe
b ret_from_exception
END(instr_service)
; ---------------------------------------------
; Memory Error Exception Handler
; ---------------------------------------------
ENTRY(mem_service)
EXCEPTION_PROLOGUE
lr r0, [efa]
mov r1, sp
FAKE_RET_FROM_EXCPN r9
bl do_memory_error
b ret_from_exception
END(mem_service)
; ---------------------------------------------
; Machine Check Exception Handler
; ---------------------------------------------
ENTRY(EV_MachineCheck)
EXCEPTION_PROLOGUE
lr r2, [ecr]
lr r0, [efa]
mov r1, sp
lsr r3, r2, 8
bmsk r3, r3, 7
brne r3, ECR_C_MCHK_DUP_TLB, 1f
bl do_tlb_overlap_fault
b ret_from_exception
1:
; DEAD END: can't do much, display Regs and HALT
SAVE_CALLEE_SAVED_USER
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r10
st sp, [r10, THREAD_CALLEE_REG]
j do_machine_check_fault
END(EV_MachineCheck)
; ---------------------------------------------
; Protection Violation Exception Handler
; ---------------------------------------------
ENTRY(EV_TLBProtV)
EXCEPTION_PROLOGUE
;---------(3) Save some more regs-----------------
; vineetg: Mar 6th: Random Seg Fault issue #1
; ecr and efa were not saved in case an Intr sneaks in
; after fake rtie
lr r2, [ecr]
lr r0, [efa] ; Faulting Data address
; --------(4) Return from CPU Exception Mode ---------
; Fake a rtie, but rtie to next label
; That way, subsequently, do_page_fault ( ) executes in pure kernel
; mode with further Exceptions enabled
FAKE_RET_FROM_EXCPN r9
mov r1, sp
;------ (5) Type of Protection Violation? ----------
;
; ProtV Hardware Exception is triggered for Access Faults of 2 types
; -Access Violaton : 00_23_(00|01|02|03)_00
; x r w r+w
; -Unaligned Access : 00_23_04_00
;
bbit1 r2, ECR_C_BIT_PROTV_MISALIG_DATA, 4f
;========= (6a) Access Violation Processing ========
bl do_page_fault
b ret_from_exception
;========== (6b) Non aligned access ============
4:
SAVE_CALLEE_SAVED_USER
mov r2, sp ; callee_regs
bl do_misaligned_access
; TBD: optimize - do this only if a callee reg was involved
; either a dst of emulated LD/ST or src with address-writeback
RESTORE_CALLEE_SAVED_USER
b ret_from_exception
END(EV_TLBProtV)
; ---------------------------------------------
; Privilege Violation Exception Handler
; ---------------------------------------------
ENTRY(EV_PrivilegeV)
EXCEPTION_PROLOGUE
lr r0, [efa]
mov r1, sp
FAKE_RET_FROM_EXCPN r9
bl do_privilege_fault
b ret_from_exception
END(EV_PrivilegeV)
; ---------------------------------------------
; Extension Instruction Exception Handler
; ---------------------------------------------
ENTRY(EV_Extension)
EXCEPTION_PROLOGUE
lr r0, [efa]
mov r1, sp
FAKE_RET_FROM_EXCPN r9
bl do_extension_fault
b ret_from_exception
END(EV_Extension)
;######################### System Call Tracing #########################
tracesys:
; save EFA in case tracer wants the PC of traced task
; using ERET won't work since next-PC has already committed
lr r12, [efa]
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r11
st r12, [r11, THREAD_FAULT_ADDR] ; thread.fault_address
; PRE Sys Call Ptrace hook
mov r0, sp ; pt_regs needed
bl @syscall_trace_entry
; Tracing code now returns the syscall num (orig or modif)
mov r8, r0
; Do the Sys Call as we normally would.
; Validate the Sys Call number
cmp r8, NR_syscalls
mov.hi r0, -ENOSYS
bhi tracesys_exit
; Restore the sys-call args. Mere invocation of the hook abv could have
; clobbered them (since they are in scratch regs). The tracer could also
; have deliberately changed the syscall args: r0-r7
ld r0, [sp, PT_r0]
ld r1, [sp, PT_r1]
ld r2, [sp, PT_r2]
ld r3, [sp, PT_r3]
ld r4, [sp, PT_r4]
ld r5, [sp, PT_r5]
ld r6, [sp, PT_r6]
ld r7, [sp, PT_r7]
ld.as r9, [sys_call_table, r8]
jl [r9] ; Entry into Sys Call Handler
tracesys_exit:
st r0, [sp, PT_r0] ; sys call return value in pt_regs
;POST Sys Call Ptrace Hook
bl @syscall_trace_exit
b ret_from_exception ; NOT ret_from_system_call at is saves r0 which
; we'd done before calling post hook above
;################### Break Point TRAP ##########################
; ======= (5b) Trap is due to Break-Point =========
trap_with_param:
; stop_pc info by gdb needs this info
lr r0, [efa]
mov r1, sp
; Now that we have read EFA, it is safe to do "fake" rtie
; and get out of CPU exception mode
FAKE_RET_FROM_EXCPN r11
; Save callee regs in case gdb wants to have a look
; SP will grow up by size of CALLEE Reg-File
; NOTE: clobbers r12
SAVE_CALLEE_SAVED_USER
; save location of saved Callee Regs @ thread_struct->pc
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r10
st sp, [r10, THREAD_CALLEE_REG]
; Call the trap handler
bl do_non_swi_trap
; unwind stack to discard Callee saved Regs
DISCARD_CALLEE_SAVED_USER
b ret_from_exception
;##################### Trap Handling ##############################
;
; EV_Trap caused by TRAP_S and TRAP0 instructions.
;------------------------------------------------------------------
; (1) System Calls
; :parameters in r0-r7.
; :r8 has the system call number
; (2) Break Points
;------------------------------------------------------------------
ENTRY(EV_Trap)
EXCEPTION_PROLOGUE
;------- (4) What caused the Trap --------------
lr r12, [ecr]
bmsk.f 0, r12, 7
bnz trap_with_param
; ======= (5a) Trap is due to System Call ========
; Before doing anything, return from CPU Exception Mode
FAKE_RET_FROM_EXCPN r11
; If syscall tracing ongoing, invoke pre-pos-hooks
GET_CURR_THR_INFO_FLAGS r10
btst r10, TIF_SYSCALL_TRACE
bnz tracesys ; this never comes back
;============ This is normal System Call case ==========
; Sys-call num shd not exceed the total system calls avail
cmp r8, NR_syscalls
mov.hi r0, -ENOSYS
bhi ret_from_system_call
; Offset into the syscall_table and call handler
ld.as r9,[sys_call_table, r8]
jl [r9] ; Entry into Sys Call Handler
; fall through to ret_from_system_call
END(EV_Trap)
ENTRY(ret_from_system_call)
st r0, [sp, PT_r0] ; sys call return value in pt_regs
; fall through yet again to ret_from_exception
;############# Return from Intr/Excp/Trap (Linux Specifics) ##############
;
; If ret to user mode do we need to handle signals, schedule() et al.
ENTRY(ret_from_exception)
; Pre-{IRQ,Trap,Exception} K/U mode from pt_regs->status32
ld r8, [sp, PT_status32] ; returning to User/Kernel Mode
bbit0 r8, STATUS_U_BIT, resume_kernel_mode
; Before returning to User mode check-for-and-complete any pending work
; such as rescheduling/signal-delivery etc.
resume_user_mode_begin:
; Disable IRQs to ensures that chk for pending work itself is atomic
; (and we don't end up missing a NEED_RESCHED/SIGPENDING due to an
; interim IRQ).
IRQ_DISABLE r10
; Fast Path return to user mode if no pending work
GET_CURR_THR_INFO_FLAGS r9
and.f 0, r9, _TIF_WORK_MASK
bz restore_regs
; --- (Slow Path #1) task preemption ---
bbit0 r9, TIF_NEED_RESCHED, .Lchk_pend_signals
mov blink, resume_user_mode_begin ; tail-call to U mode ret chks
b @schedule ; BTST+Bnz causes relo error in link
.Lchk_pend_signals:
IRQ_ENABLE r10
; --- (Slow Path #2) pending signal ---
mov r0, sp ; pt_regs for arg to do_signal()/do_notify_resume()
GET_CURR_THR_INFO_FLAGS r9
bbit0 r9, TIF_SIGPENDING, .Lchk_notify_resume
; Normal Trap/IRQ entry only saves Scratch (caller-saved) regs
; in pt_reg since the "C" ABI (kernel code) will automatically
; save/restore callee-saved regs.
;
; However, here we need to explicitly save callee regs because
; (i) If this signal causes coredump - full regfile needed
; (ii) If signal is SIGTRAP/SIGSTOP, task is being traced thus
; tracer might call PEEKUSR(CALLEE reg)
;
; NOTE: SP will grow up by size of CALLEE Reg-File
SAVE_CALLEE_SAVED_USER ; clobbers r12
; save location of saved Callee Regs @ thread_struct->callee
GET_CURR_TASK_FIELD_PTR TASK_THREAD, r10
st sp, [r10, THREAD_CALLEE_REG]
bl @do_signal
; Ideally we want to discard the Callee reg above, however if this was
; a tracing signal, tracer could have done a POKEUSR(CALLEE reg)
RESTORE_CALLEE_SAVED_USER
b resume_user_mode_begin ; loop back to start of U mode ret
; --- (Slow Path #3) notify_resume ---
.Lchk_notify_resume:
btst r9, TIF_NOTIFY_RESUME
blnz @do_notify_resume
b resume_user_mode_begin ; unconditionally back to U mode ret chks
; for single exit point from this block
resume_kernel_mode:
; Disable Interrupts from this point on
; CONFIG_PREEMPT: This is a must for preempt_schedule_irq()
; !CONFIG_PREEMPT: To ensure restore_regs is intr safe
IRQ_DISABLE r9
#ifdef CONFIG_PREEMPT
; Can't preempt if preemption disabled
GET_CURR_THR_INFO_FROM_SP r10
ld r8, [r10, THREAD_INFO_PREEMPT_COUNT]
brne r8, 0, restore_regs
; check if this task's NEED_RESCHED flag set
ld r9, [r10, THREAD_INFO_FLAGS]
bbit0 r9, TIF_NEED_RESCHED, restore_regs
; Invoke PREEMPTION
bl preempt_schedule_irq
; preempt_schedule_irq() always returns with IRQ disabled
#endif
; fall through
;############# Return from Intr/Excp/Trap (ARC Specifics) ##############
;
; Restore the saved sys context (common exit-path for EXCPN/IRQ/Trap)
; IRQ shd definitely not happen between now and rtie
; All 2 entry points to here already disable interrupts
restore_regs :
TRACE_ASM_IRQ_ENABLE
lr r10, [status32]
; Restore REG File. In case multiple Events outstanding,
; use the same priorty as rtie: EXCPN, L2 IRQ, L1 IRQ, None
; Note that we use realtime STATUS32 (not pt_regs->status32) to
; decide that.
; if Returning from Exception
bbit0 r10, STATUS_AE_BIT, not_exception
RESTORE_ALL_SYS
rtie
; Not Exception so maybe Interrupts (Level 1 or 2)
not_exception:
#ifdef CONFIG_ARC_COMPACT_IRQ_LEVELS
; Level 2 interrupt return Path - from hardware standpoint
bbit0 r10, STATUS_A2_BIT, not_level2_interrupt
;------------------------------------------------------------------
; However the context returning might not have taken L2 intr itself
; e.g. Task'A' user-code -> L2 intr -> schedule -> 'B' user-code ret
; Special considerations needed for the context which took L2 intr
ld r9, [sp, PT_event] ; Ensure this is L2 intr context
brne r9, event_IRQ2, 149f
;------------------------------------------------------------------
; if L2 IRQ interrupted an L1 ISR, we'd disabled preemption earlier
; so that sched doesn't move to new task, causing L1 to be delayed
; undeterministically. Now that we've achieved that, let's reset
; things to what they were, before returning from L2 context
;----------------------------------------------------------------
ld r9, [sp, PT_status32] ; get statu32_l2 (saved in pt_regs)
bbit0 r9, STATUS_A1_BIT, 149f ; L1 not active when L2 IRQ, so normal
; decrement thread_info->preempt_count (re-enable preemption)
GET_CURR_THR_INFO_FROM_SP r10
ld r9, [r10, THREAD_INFO_PREEMPT_COUNT]
; paranoid check, given A1 was active when A2 happened, preempt count
; must not be 0 because we would have incremented it.
; If this does happen we simply HALT as it means a BUG !!!
cmp r9, 0
bnz 2f
flag 1
2:
sub r9, r9, 1
st r9, [r10, THREAD_INFO_PREEMPT_COUNT]
149:
;return from level 2
RESTORE_ALL_INT2
debug_marker_l2:
rtie
not_level2_interrupt:
#endif
bbit0 r10, STATUS_A1_BIT, not_level1_interrupt
;return from level 1
RESTORE_ALL_INT1
debug_marker_l1:
rtie
not_level1_interrupt:
;this case is for syscalls or Exceptions (with fake rtie)
RESTORE_ALL_SYS
debug_marker_syscall:
rtie
END(ret_from_exception)
ENTRY(ret_from_fork)
; when the forked child comes here from the __switch_to function
; r0 has the last task pointer.
; put last task in scheduler queue
bl @schedule_tail
ld r9, [sp, PT_status32]
brne r9, 0, 1f
jl.d [r14] ; kernel thread entry point
mov r0, r13 ; (see PF_KTHREAD block in copy_thread)
1:
; Return to user space
; 1. Any forked task (Reach here via BRne above)
; 2. First ever init task (Reach here via return from JL above)
; This is the historic "kernel_execve" use-case, to return to init
; user mode, in a round about way since that is always done from
; a kernel thread which is executed via JL above but always returns
; out whenever kernel_execve (now inline do_fork()) is involved
b ret_from_exception
END(ret_from_fork)
;################### Special Sys Call Wrappers ##########################
ENTRY(sys_clone_wrapper)
SAVE_CALLEE_SAVED_USER
bl @sys_clone
DISCARD_CALLEE_SAVED_USER
GET_CURR_THR_INFO_FLAGS r10
btst r10, TIF_SYSCALL_TRACE
bnz tracesys_exit
b ret_from_system_call
END(sys_clone_wrapper)
#ifdef CONFIG_ARC_DW2_UNWIND
; Workaround for bug 94179 (STAR ):
; Despite -fasynchronous-unwind-tables, linker is not making dwarf2 unwinder
; section (.debug_frame) as loadable. So we force it here.
; This also fixes STAR 9000487933 where the prev-workaround (objcopy --setflag)
; would not work after a clean build due to kernel build system dependencies.
.section .debug_frame, "wa",@progbits
#endif
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