/* 
 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
 * 
 * System call entry code / Linux gateway page
 * Copyright (c) Matthew Wilcox 1999 <willy@infradead.org>
 * Licensed under the GNU GPL.
 * thanks to Philipp Rumpf, Mike Shaver and various others
 * sorry about the wall, puffin..
 */

/*
How does the Linux gateway page on PA-RISC work?
------------------------------------------------
The Linux gateway page on PA-RISC is "special".
It actually has PAGE_GATEWAY bits set (this is linux terminology; in parisc
terminology it's Execute, promote to PL0) in the page map.  So anything
executing on this page executes with kernel level privilege (there's more to it
than that: to have this happen, you also have to use a branch with a ,gate
completer to activate the privilege promotion).  The upshot is that everything
that runs on the gateway page runs at kernel privilege but with the current
user process address space (although you have access to kernel space via %sr2).
For the 0x100 syscall entry, we redo the space registers to point to the kernel
address space (preserving the user address space in %sr3), move to wide mode if
required, save the user registers and branch into the kernel syscall entry
point.  For all the other functions, we execute at kernel privilege but don't
flip address spaces. The basic upshot of this is that these code snippets are
executed atomically (because the kernel can't be pre-empted) and they may
perform architecturally forbidden (to PL3) operations (like setting control
registers).
*/


#include <asm/asm-offsets.h>
#include <asm/unistd.h>
#include <asm/errno.h>
#include <asm/page.h>
#include <asm/psw.h>
#include <asm/thread_info.h>
#include <asm/assembly.h>
#include <asm/processor.h>
#include <asm/cache.h>
#include <asm/spinlock_types.h>

#include <linux/linkage.h>

        /* We fill the empty parts of the gateway page with
         * something that will kill the kernel or a
         * userspace application.
         */
#define KILL_INSN       break   0,0

        .level          PA_ASM_LEVEL

        .macro  lws_pagefault_disable reg1,reg2
        mfctl   %cr30, \reg2
        ldo     TASK_PAGEFAULT_DISABLED(\reg2), \reg2
        ldw     0(%sr2,\reg2), \reg1
        ldo     1(\reg1), \reg1
        stw     \reg1, 0(%sr2,\reg2)
        .endm

        .macro  lws_pagefault_enable reg1,reg2
        mfctl   %cr30, \reg2
        ldo     TASK_PAGEFAULT_DISABLED(\reg2), \reg2
        ldw     0(%sr2,\reg2), \reg1
        ldo     -1(\reg1), \reg1
        stw     \reg1, 0(%sr2,\reg2)
        .endm

        /* raise exception if spinlock content is not zero or
         * __ARCH_SPIN_LOCK_UNLOCKED_VAL */
        .macro  spinlock_check spin_val,tmpreg
#ifdef CONFIG_LIGHTWEIGHT_SPINLOCK_CHECK
        ldi     __ARCH_SPIN_LOCK_UNLOCKED_VAL, \tmpreg
        andcm,= \spin_val, \tmpreg, %r0
        .word   SPINLOCK_BREAK_INSN
#endif
        .endm

        .text

        .import syscall_exit,code
        .import syscall_exit_rfi,code

        /* Linux gateway page is aliased to virtual page 0 in the kernel
         * address space. Since it is a gateway page it cannot be
         * dereferenced, so null pointers will still fault. We start
         * the actual entry point at 0x100. We put break instructions
         * at the beginning of the page to trap null indirect function
         * pointers.
         */

        .align PAGE_SIZE
ENTRY(linux_gateway_page)

        /* ADDRESS 0x00 to 0xb0 = 176 bytes / 4 bytes per insn = 44 insns */
        .rept 44
        KILL_INSN
        .endr

        /* ADDRESS 0xb0 to 0xb8, lws uses two insns for entry */
        /* Light-weight-syscall entry must always be located at 0xb0 */
        /* WARNING: Keep this number updated with table size changes */
#define __NR_lws_entries (5)

lws_entry:
        gate    lws_start, %r0          /* increase privilege */
        depi    PRIV_USER, 31, 2, %r31  /* Ensure we return into user mode. */

        /* Fill from 0xb8 to 0xe0 */
        .rept 10
        KILL_INSN
        .endr

        /* This function MUST be located at 0xe0 for glibc's threading 
        mechanism to work. DO NOT MOVE THIS CODE EVER! */
set_thread_pointer:
        gate    .+8, %r0                /* increase privilege */
        depi    PRIV_USER, 31, 2, %r31  /* Ensure we return into user mode. */
        be      0(%sr7,%r31)            /* return to user space */
        mtctl   %r26, %cr27             /* move arg0 to the control register */

        /* Increase the chance of trapping if random jumps occur to this
        address, fill from 0xf0 to 0x100 */
        .rept 4
        KILL_INSN
        .endr

/* This address must remain fixed at 0x100 for glibc's syscalls to work */
        .align LINUX_GATEWAY_ADDR
linux_gateway_entry:
        gate    .+8, %r0                        /* become privileged */
        mtsp    %r0,%sr4                        /* get kernel space into sr4 */
        mtsp    %r0,%sr5                        /* get kernel space into sr5 */
        mtsp    %r0,%sr6                        /* get kernel space into sr6 */

#ifdef CONFIG_64BIT
        /* Store W bit on entry to the syscall in case it's a wide userland
         * process. */
        ssm     PSW_SM_W, %r1
        extrd,u %r1,PSW_W_BIT,1,%r1
        /* sp must be aligned on 4, so deposit the W bit setting into
         * the bottom of sp temporarily */
        or,ev   %r1,%r30,%r30
        b,n     1f
        /* The top halves of argument registers must be cleared on syscall
         * entry from narrow executable.
         */
        depdi   0, 31, 32, %r26
        depdi   0, 31, 32, %r25
        depdi   0, 31, 32, %r24
        depdi   0, 31, 32, %r23
        depdi   0, 31, 32, %r22
        depdi   0, 31, 32, %r21
1:      
#endif

        /* We use a rsm/ssm pair to prevent sr3 from being clobbered
         * by external interrupts.
         */
        mfsp    %sr7,%r1                        /* save user sr7 */
        rsm     PSW_SM_I, %r0                   /* disable interrupts */
        mtsp    %r1,%sr3                        /* and store it in sr3 */

        mfctl   %cr30,%r1
        xor     %r1,%r30,%r30                   /* ye olde xor trick */
        xor     %r1,%r30,%r1
        xor     %r1,%r30,%r30

        LDREG   TASK_STACK(%r30),%r30           /* set up kernel stack */
        ldo     FRAME_SIZE(%r30),%r30
        /* N.B.: It is critical that we don't set sr7 to 0 until r30
         *       contains a valid kernel stack pointer. It is also
         *       critical that we don't start using the kernel stack
         *       until after sr7 has been set to 0.
         */

        mtsp    %r0,%sr7                        /* get kernel space into sr7 */
        ssm     PSW_SM_I, %r0                   /* enable interrupts */
        STREGM  %r1,FRAME_SIZE(%r30)            /* save r1 (usp) here for now */
        mfctl   %cr30,%r1                       /* get task ptr in %r1 */

        /* Save some registers for sigcontext and potential task
           switch (see entry.S for the details of which ones are
           saved/restored).  TASK_PT_PSW is zeroed so we can see whether
           a process is on a syscall or not.  For an interrupt the real
           PSW value is stored.  This is needed for gdb and sys_ptrace. */
        STREG   %r0,  TASK_PT_PSW(%r1)
        STREG   %r2,  TASK_PT_GR2(%r1)          /* preserve rp */
        STREG   %r19, TASK_PT_GR19(%r1)

        LDREGM  -FRAME_SIZE(%r30), %r2          /* get users sp back */
#ifdef CONFIG_64BIT
        extrd,u %r2,63,1,%r19                   /* W hidden in bottom bit */
#if 0
        xor     %r19,%r2,%r2                    /* clear bottom bit */
        depd,z  %r19,1,1,%r19
        std     %r19,TASK_PT_PSW(%r1)
#endif
#endif
        STREG   %r2,  TASK_PT_GR30(%r1)         /* ... and save it */
        
        STREG   %r20, TASK_PT_GR20(%r1)         /* Syscall number */
        STREG   %r21, TASK_PT_GR21(%r1)
        STREG   %r22, TASK_PT_GR22(%r1)
        STREG   %r23, TASK_PT_GR23(%r1)         /* 4th argument */
        STREG   %r24, TASK_PT_GR24(%r1)         /* 3rd argument */
        STREG   %r25, TASK_PT_GR25(%r1)         /* 2nd argument */
        STREG   %r26, TASK_PT_GR26(%r1)         /* 1st argument */
        STREG   %r27, TASK_PT_GR27(%r1)         /* user dp */
        STREG   %r28, TASK_PT_GR28(%r1)         /* return value 0 */
        STREG   %r0, TASK_PT_ORIG_R28(%r1)      /* don't prohibit restarts */
        STREG   %r29, TASK_PT_GR29(%r1)         /* return value 1 */
        STREG   %r31, TASK_PT_GR31(%r1)         /* preserve syscall return ptr */
        
        ldo     TASK_PT_FR0(%r1), %r27          /* save fpregs from the kernel */
        save_fp %r27                            /* or potential task switch  */

        mfctl   %cr11, %r27                     /* i.e. SAR */
        STREG   %r27, TASK_PT_SAR(%r1)

        loadgp

#ifdef CONFIG_64BIT
        ldo     -16(%r30),%r29                  /* Reference param save area */
        copy    %r19,%r2                        /* W bit back to r2 */
#else
        /* no need to save these on stack in wide mode because the first 8
         * args are passed in registers */
        stw     %r22, -52(%r30)                 /* 5th argument */
        stw     %r21, -56(%r30)                 /* 6th argument */
#endif

        /* Are we being ptraced? */
        mfctl   %cr30, %r1
        LDREG   TASK_TI_FLAGS(%r1),%r1
        ldi     _TIF_SYSCALL_TRACE_MASK, %r19
        and,COND(=) %r1, %r19, %r0
        b,n     .Ltracesys
        
        /* Note!  We cannot use the syscall table that is mapped
        nearby since the gateway page is mapped execute-only. */

#ifdef CONFIG_64BIT
        ldil    L%sys_call_table, %r1
        or,ev   %r2,%r2,%r2
        ldil    L%sys_call_table64, %r1
        ldo     R%sys_call_table(%r1), %r19
        or,ev   %r2,%r2,%r2
        ldo     R%sys_call_table64(%r1), %r19
#else
        load32  sys_call_table, %r19
#endif  
        comiclr,>>      __NR_Linux_syscalls, %r20, %r0
        b,n     .Lsyscall_nosys
        
        LDREGX  %r20(%r19), %r19

        /* If this is a sys_rt_sigreturn call, and the signal was received
         * when not in_syscall, then we want to return via syscall_exit_rfi,
         * not syscall_exit.  Signal no. in r20, in_syscall in r25 (see
         * trampoline code in signal.c).
         */
        ldi     __NR_rt_sigreturn,%r2
        comb,=  %r2,%r20,.Lrt_sigreturn
.Lin_syscall:
        ldil    L%syscall_exit,%r2
        be      0(%sr7,%r19)
        ldo     R%syscall_exit(%r2),%r2
.Lrt_sigreturn:
        comib,<> 0,%r25,.Lin_syscall
        ldil    L%syscall_exit_rfi,%r2
        be      0(%sr7,%r19)
        ldo     R%syscall_exit_rfi(%r2),%r2

        /* Note!  Because we are not running where we were linked, any
        calls to functions external to this file must be indirect.  To
        be safe, we apply the opposite rule to functions within this
        file, with local labels given to them to ensure correctness. */
        
.Lsyscall_nosys:
syscall_nosys:
        ldil    L%syscall_exit,%r1
        be      R%syscall_exit(%sr7,%r1)
        ldo     -ENOSYS(%r0),%r28                  /* set errno */


/* Warning! This trace code is a virtual duplicate of the code above so be
 * sure to maintain both! */
.Ltracesys:
tracesys:
        /* Need to save more registers so the debugger can see where we
         * are.  This saves only the lower 8 bits of PSW, so that the C
         * bit is still clear on syscalls, and the D bit is set if this
         * full register save path has been executed.  We check the D
         * bit on syscall_return_rfi to determine which registers to
         * restore.  An interrupt results in a full PSW saved with the
         * C bit set, a non-straced syscall entry results in C and D clear
         * in the saved PSW.
         */
        mfctl   %cr30,%r1                       /* get task ptr */
        ssm     0,%r2
        STREG   %r2,TASK_PT_PSW(%r1)            /* Lower 8 bits only!! */
        mfsp    %sr0,%r2
        STREG   %r2,TASK_PT_SR0(%r1)
        mfsp    %sr1,%r2
        STREG   %r2,TASK_PT_SR1(%r1)
        mfsp    %sr2,%r2
        STREG   %r2,TASK_PT_SR2(%r1)
        mfsp    %sr3,%r2
        STREG   %r2,TASK_PT_SR3(%r1)
        STREG   %r2,TASK_PT_SR4(%r1)
        STREG   %r2,TASK_PT_SR5(%r1)
        STREG   %r2,TASK_PT_SR6(%r1)
        STREG   %r2,TASK_PT_SR7(%r1)
        STREG   %r2,TASK_PT_IASQ0(%r1)
        STREG   %r2,TASK_PT_IASQ1(%r1)
        LDREG   TASK_PT_GR31(%r1),%r2
        STREG   %r2,TASK_PT_IAOQ0(%r1)
        ldo     4(%r2),%r2
        STREG   %r2,TASK_PT_IAOQ1(%r1)
        ldo     TASK_REGS(%r1),%r2
        /* reg_save %r2 */
        STREG   %r3,PT_GR3(%r2)
        STREG   %r4,PT_GR4(%r2)
        STREG   %r5,PT_GR5(%r2)
        STREG   %r6,PT_GR6(%r2)
        STREG   %r7,PT_GR7(%r2)
        STREG   %r8,PT_GR8(%r2)
        STREG   %r9,PT_GR9(%r2)
        STREG   %r10,PT_GR10(%r2)
        STREG   %r11,PT_GR11(%r2)
        STREG   %r12,PT_GR12(%r2)
        STREG   %r13,PT_GR13(%r2)
        STREG   %r14,PT_GR14(%r2)
        STREG   %r15,PT_GR15(%r2)
        STREG   %r16,PT_GR16(%r2)
        STREG   %r17,PT_GR17(%r2)
        STREG   %r18,PT_GR18(%r2)
        /* Finished saving things for the debugger */

        copy    %r2,%r26
        ldil    L%do_syscall_trace_enter,%r1
        ldil    L%tracesys_next,%r2
        be      R%do_syscall_trace_enter(%sr7,%r1)
        ldo     R%tracesys_next(%r2),%r2
        
tracesys_next:
        /* do_syscall_trace_enter either returned the syscallno, or -1L,
         *  so we skip restoring the PT_GR20 below, since we pulled it from
         *  task->thread.regs.gr[20] above.
         */
        copy    %ret0,%r20

        mfctl   %cr30,%r1                       /* get task ptr */
        LDREG   TASK_PT_GR28(%r1), %r28         /* Restore return value */
        LDREG   TASK_PT_GR26(%r1), %r26         /* Restore the users args */
        LDREG   TASK_PT_GR25(%r1), %r25
        LDREG   TASK_PT_GR24(%r1), %r24
        LDREG   TASK_PT_GR23(%r1), %r23
        LDREG   TASK_PT_GR22(%r1), %r22
        LDREG   TASK_PT_GR21(%r1), %r21
#ifdef CONFIG_64BIT
        ldo     -16(%r30),%r29                  /* Reference param save area */
#else
        stw     %r22, -52(%r30)                 /* 5th argument */
        stw     %r21, -56(%r30)                 /* 6th argument */
#endif

        cmpib,COND(=),n -1,%r20,tracesys_exit /* seccomp may have returned -1 */
        comiclr,>>      __NR_Linux_syscalls, %r20, %r0
        b,n     .Ltracesys_nosys

        /* Note!  We cannot use the syscall table that is mapped
        nearby since the gateway page is mapped execute-only. */

#ifdef CONFIG_64BIT
        LDREG   TASK_PT_GR30(%r1), %r19         /* get users sp back */
        extrd,u %r19,63,1,%r2                   /* W hidden in bottom bit */

        ldil    L%sys_call_table, %r1
        or,ev   %r2,%r2,%r2
        ldil    L%sys_call_table64, %r1
        ldo     R%sys_call_table(%r1), %r19
        or,ev   %r2,%r2,%r2
        ldo     R%sys_call_table64(%r1), %r19
#else
        load32  sys_call_table, %r19
#endif

        LDREGX  %r20(%r19), %r19

        /* If this is a sys_rt_sigreturn call, and the signal was received
         * when not in_syscall, then we want to return via syscall_exit_rfi,
         * not syscall_exit.  Signal no. in r20, in_syscall in r25 (see
         * trampoline code in signal.c).
         */
        ldi     __NR_rt_sigreturn,%r2
        comb,=  %r2,%r20,.Ltrace_rt_sigreturn
.Ltrace_in_syscall:
        ldil    L%tracesys_exit,%r2
        be      0(%sr7,%r19)
        ldo     R%tracesys_exit(%r2),%r2

.Ltracesys_nosys:
        ldo     -ENOSYS(%r0),%r28               /* set errno */

        /* Do *not* call this function on the gateway page, because it
        makes a direct call to syscall_trace. */
        
tracesys_exit:
        mfctl   %cr30,%r1                       /* get task ptr */
#ifdef CONFIG_64BIT
        ldo     -16(%r30),%r29                  /* Reference param save area */
#endif
        ldo     TASK_REGS(%r1),%r26
        BL      do_syscall_trace_exit,%r2
        STREG   %r28,TASK_PT_GR28(%r1)          /* save return value now */
        mfctl   %cr30,%r1                       /* get task ptr */
        LDREG   TASK_PT_GR28(%r1), %r28         /* Restore return val. */

        ldil    L%syscall_exit,%r1
        be,n    R%syscall_exit(%sr7,%r1)

.Ltrace_rt_sigreturn:
        comib,<> 0,%r25,.Ltrace_in_syscall
        ldil    L%tracesys_sigexit,%r2
        be      0(%sr7,%r19)
        ldo     R%tracesys_sigexit(%r2),%r2

tracesys_sigexit:
        mfctl   %cr30,%r1                       /* get task ptr */
#ifdef CONFIG_64BIT
        ldo     -16(%r30),%r29                  /* Reference param save area */
#endif
        BL      do_syscall_trace_exit,%r2
        ldo     TASK_REGS(%r1),%r26

        ldil    L%syscall_exit_rfi,%r1
        be,n    R%syscall_exit_rfi(%sr7,%r1)


        /*********************************************************
                32/64-bit Light-Weight-Syscall ABI

                * - Indicates a hint for userspace inline asm
                implementations.

                Syscall number (caller-saves)
                - %r20
                * In asm clobber.

                Argument registers (caller-saves)
                - %r26, %r25, %r24, %r23, %r22
                * In asm input.

                Return registers (caller-saves)
                - %r28 (return), %r21 (errno)
                * In asm output.

                Caller-saves registers
                - %r1, %r27, %r29
                - %r2 (return pointer)
                - %r31 (ble link register)
                * In asm clobber.

                Callee-saves registers
                - %r3-%r18
                - %r30 (stack pointer)
                * Not in asm clobber.

                If userspace is 32-bit:
                Callee-saves registers
                - %r19 (32-bit PIC register)

                Differences from 32-bit calling convention:
                - Syscall number in %r20
                - Additional argument register %r22 (arg4)
                - Callee-saves %r19.

                If userspace is 64-bit:
                Callee-saves registers
                - %r27 (64-bit PIC register)

                Differences from 64-bit calling convention:
                - Syscall number in %r20
                - Additional argument register %r22 (arg4)
                - Callee-saves %r27.

                Error codes returned by entry path:

                ENOSYS - r20 was an invalid LWS number.

        *********************************************************/
lws_start:

#ifdef CONFIG_64BIT
        ssm     PSW_SM_W, %r1
        extrd,u %r1,PSW_W_BIT,1,%r1
        /* sp must be aligned on 4, so deposit the W bit setting into
         * the bottom of sp temporarily */
        or,od   %r1,%r30,%r30

        /* Clip LWS number to a 32-bit value for 32-bit processes */
        depdi   0, 31, 32, %r20
#endif  

        /* Is the lws entry number valid? */
        comiclr,>>      __NR_lws_entries, %r20, %r0
        b,n     lws_exit_nosys

        /* Load table start */
        ldil    L%lws_table, %r1
        ldo     R%lws_table(%r1), %r28  /* Scratch use of r28 */
        LDREGX  %r20(%sr2,r28), %r21    /* Scratch use of r21 */

        /* Jump to lws, lws table pointers already relocated */
        be,n    0(%sr2,%r21)

lws_exit_noerror:
        lws_pagefault_enable    %r1,%r21
        ldi     __ARCH_SPIN_LOCK_UNLOCKED_VAL, %r21
        stw,ma  %r21, 0(%sr2,%r20)
        ssm     PSW_SM_I, %r0
        b       lws_exit
        copy    %r0, %r21

lws_wouldblock:
        ssm     PSW_SM_I, %r0
        ldo     2(%r0), %r28
        b       lws_exit
        ldo     -EAGAIN(%r0), %r21

lws_pagefault:
        lws_pagefault_enable    %r1,%r21
        ldi     __ARCH_SPIN_LOCK_UNLOCKED_VAL, %r21
        stw,ma  %r21, 0(%sr2,%r20)
        ssm     PSW_SM_I, %r0
        ldo     3(%r0),%r28
        b       lws_exit
        ldo     -EAGAIN(%r0),%r21

lws_fault:
        ldo     1(%r0),%r28
        b       lws_exit
        ldo     -EFAULT(%r0),%r21

lws_exit_nosys:
        ldo     -ENOSYS(%r0),%r21
        /* Fall through: Return to userspace */

lws_exit:
#ifdef CONFIG_64BIT
        /* decide whether to reset the wide mode bit
         *
         * For a syscall, the W bit is stored in the lowest bit
         * of sp.  Extract it and reset W if it is zero */
        extrd,u,*<>     %r30,63,1,%r1
        rsm     PSW_SM_W, %r0
        /* now reset the lowest bit of sp if it was set */
        xor     %r30,%r1,%r30
#endif
        be,n    0(%sr7, %r31)


        
        /***************************************************
                Implementing 32bit CAS as an atomic operation:

                %r26 - Address to examine
                %r25 - Old value to check (old)
                %r24 - New value to set (new)
                %r28 - Return prev through this register.
                %r21 - Kernel error code

                %r21 returns the following error codes:
                EAGAIN - CAS is busy, ldcw failed, try again.
                EFAULT - Read or write failed.          

                If EAGAIN is returned, %r28 indicates the busy reason:
                r28 == 1 - CAS is busy. lock contended.
                r28 == 2 - CAS is busy. ldcw failed.
                r28 == 3 - CAS is busy. page fault.

                Scratch: r20, r28, r1

        ****************************************************/

        /* ELF64 Process entry path */
lws_compare_and_swap64:
#ifdef CONFIG_64BIT
        b,n     lws_compare_and_swap
#else
        /* If we are not a 64-bit kernel, then we don't
         * have 64-bit input registers, and calling
         * the 64-bit LWS CAS returns ENOSYS.
         */
        b,n     lws_exit_nosys
#endif

        /* ELF32/ELF64 Process entry path */
lws_compare_and_swap32:
#ifdef CONFIG_64BIT
        /* Wide mode user process? */
        bb,<,n  %sp, 31, lws_compare_and_swap

        /* Clip all the input registers for 32-bit processes */
        depdi   0, 31, 32, %r26
        depdi   0, 31, 32, %r25
        depdi   0, 31, 32, %r24
#endif

lws_compare_and_swap:
        /* Trigger memory reference interruptions without writing to memory */
1:      ldw     0(%r26), %r28
        proberi (%r26), PRIV_USER, %r28
        comb,=,n        %r28, %r0, lws_fault /* backwards, likely not taken */
        nop
2:      stbys,e %r0, 0(%r26)

        /* Calculate 8-bit hash index from virtual address */
        extru_safe      %r26, 27, 8, %r20

        /* Load start of lock table */
        ldil    L%lws_lock_start, %r28
        ldo     R%lws_lock_start(%r28), %r28

        /* Find lock to use, the hash index is one of 0 to
           255, multiplied by 16 (keep it 16-byte aligned)
           and add to the lock table offset. */
        shlw    %r20, 4, %r20
        add     %r20, %r28, %r20

        rsm     PSW_SM_I, %r0                           /* Disable interrupts */

        /* Try to acquire the lock */
        LDCW    0(%sr2,%r20), %r28
        spinlock_check  %r28, %r21
        comclr,<>       %r0, %r28, %r0
        b,n     lws_wouldblock

        /* Disable page faults to prevent sleeping in critical region */
        lws_pagefault_disable   %r21,%r28

        /*
                prev = *addr;
                if ( prev == old )
                  *addr = new;
                return prev;
        */

        /* NOTES:
                This all works because intr_do_signal
                and schedule both check the return iasq
                and see that we are on the kernel page
                so this process is never scheduled off
                or is ever sent any signal of any sort,
                thus it is wholly atomic from usrspace's
                perspective
        */
        /* The load and store could fail */
3:      ldw     0(%r26), %r28
        sub,<>  %r28, %r25, %r0
4:      stw     %r24, 0(%r26)
        b,n     lws_exit_noerror

        /* A fault occurred on load or stbys,e store */
5:      b,n     lws_fault
        ASM_EXCEPTIONTABLE_ENTRY(1b-linux_gateway_page, 5b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(2b-linux_gateway_page, 5b-linux_gateway_page)

        /* A page fault occurred in critical region */
6:      b,n     lws_pagefault
        ASM_EXCEPTIONTABLE_ENTRY(3b-linux_gateway_page, 6b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(4b-linux_gateway_page, 6b-linux_gateway_page)


        /***************************************************
                New CAS implementation which uses pointers and variable size
                information. The value pointed by old and new MUST NOT change
                while performing CAS. The lock only protects the value at %r26.

                %r26 - Address to examine
                %r25 - Pointer to the value to check (old)
                %r24 - Pointer to the value to set (new)
                %r23 - Size of the variable (0/1/2/3 for 8/16/32/64 bit)
                %r28 - Return non-zero on failure
                %r21 - Kernel error code

                %r21 returns the following error codes:
                EAGAIN - CAS is busy, ldcw failed, try again.
                EFAULT - Read or write failed.

                If EAGAIN is returned, %r28 indicates the busy reason:
                r28 == 1 - CAS is busy. lock contended.
                r28 == 2 - CAS is busy. ldcw failed.
                r28 == 3 - CAS is busy. page fault.

                Scratch: r20, r22, r28, r29, r1, fr4 (32bit for 64bit CAS only)

        ****************************************************/

lws_compare_and_swap_2:
#ifdef CONFIG_64BIT
        /* Wide mode user process? */
        bb,<,n  %sp, 31, cas2_begin

        /* Clip the input registers for 32-bit processes. We don't
           need to clip %r23 as we only use it for word operations */
        depdi   0, 31, 32, %r26
        depdi   0, 31, 32, %r25
        depdi   0, 31, 32, %r24
#endif

cas2_begin:
        /* Check the validity of the size pointer */
        subi,>>= 3, %r23, %r0
        b,n     lws_exit_nosys

        /* Jump to the functions which will load the old and new values into
           registers depending on the their size */
        shlw    %r23, 2, %r29
        blr     %r29, %r0
        nop

        /* 8-bit load */
1:      ldb     0(%r25), %r25
        b       cas2_lock_start
2:      ldb     0(%r24), %r24
        nop
        nop
        nop
        nop
        nop

        /* 16-bit load */
3:      ldh     0(%r25), %r25
        b       cas2_lock_start
4:      ldh     0(%r24), %r24
        nop
        nop
        nop
        nop
        nop

        /* 32-bit load */
5:      ldw     0(%r25), %r25
        b       cas2_lock_start
6:      ldw     0(%r24), %r24
        nop
        nop
        nop
        nop
        nop

        /* 64-bit load */
#ifdef CONFIG_64BIT
7:      ldd     0(%r25), %r25
8:      ldd     0(%r24), %r24
#else
        /* Load old value into r22/r23 - high/low */
7:      ldw     0(%r25), %r22
8:      ldw     4(%r25), %r23
        /* Load new value into fr4 for atomic store later */
9:      flddx   0(%r24), %fr4
#endif

cas2_lock_start:
        /* Trigger memory reference interruptions without writing to memory */
        copy    %r26, %r28
        depi_safe       0, 31, 2, %r28
10:     ldw     0(%r28), %r1
        proberi (%r28), PRIV_USER, %r1
        comb,=,n        %r1, %r0, lws_fault /* backwards, likely not taken */
        nop
11:     stbys,e %r0, 0(%r28)

        /* Calculate 8-bit hash index from virtual address */
        extru_safe      %r26, 27, 8, %r20

        /* Load start of lock table */
        ldil    L%lws_lock_start, %r28
        ldo     R%lws_lock_start(%r28), %r28

        /* Find lock to use, the hash index is one of 0 to
           255, multiplied by 16 (keep it 16-byte aligned)
           and add to the lock table offset. */
        shlw    %r20, 4, %r20
        add     %r20, %r28, %r20

        rsm     PSW_SM_I, %r0                   /* Disable interrupts */

        /* Try to acquire the lock */
        LDCW    0(%sr2,%r20), %r28
        spinlock_check  %r28, %r21
        comclr,<>       %r0, %r28, %r0
        b,n     lws_wouldblock

        /* Disable page faults to prevent sleeping in critical region */
        lws_pagefault_disable   %r21,%r28

        /*
                prev = *addr;
                if ( prev == old )
                  *addr = new;
                return prev;
        */

        /* NOTES:
                This all works because intr_do_signal
                and schedule both check the return iasq
                and see that we are on the kernel page
                so this process is never scheduled off
                or is ever sent any signal of any sort,
                thus it is wholly atomic from usrspace's
                perspective
        */

        /* Jump to the correct function */
        blr     %r29, %r0
        /* Set %r28 as non-zero for now */
        ldo     1(%r0),%r28

        /* 8-bit CAS */
12:     ldb     0(%r26), %r29
        sub,=   %r29, %r25, %r0
        b,n     lws_exit_noerror
13:     stb     %r24, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28
        nop
        nop

        /* 16-bit CAS */
14:     ldh     0(%r26), %r29
        sub,=   %r29, %r25, %r0
        b,n     lws_exit_noerror
15:     sth     %r24, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28
        nop
        nop

        /* 32-bit CAS */
16:     ldw     0(%r26), %r29
        sub,=   %r29, %r25, %r0
        b,n     lws_exit_noerror
17:     stw     %r24, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28
        nop
        nop

        /* 64-bit CAS */
#ifdef CONFIG_64BIT
18:     ldd     0(%r26), %r29
        sub,*=  %r29, %r25, %r0
        b,n     lws_exit_noerror
19:     std     %r24, 0(%r26)
        copy    %r0, %r28
#else
        /* Compare first word */
18:     ldw     0(%r26), %r29
        sub,=   %r29, %r22, %r0
        b,n     lws_exit_noerror
        /* Compare second word */
19:     ldw     4(%r26), %r29
        sub,=   %r29, %r23, %r0
        b,n     lws_exit_noerror
        /* Perform the store */
20:     fstdx   %fr4, 0(%r26)
        copy    %r0, %r28
#endif
        b       lws_exit_noerror
        copy    %r0, %r28

        /* A fault occurred on load or stbys,e store */
30:     b,n     lws_fault
        ASM_EXCEPTIONTABLE_ENTRY(1b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(2b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(3b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(4b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(5b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(6b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(7b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(8b-linux_gateway_page, 30b-linux_gateway_page)
#ifndef CONFIG_64BIT
        ASM_EXCEPTIONTABLE_ENTRY(9b-linux_gateway_page, 30b-linux_gateway_page)
#endif

        ASM_EXCEPTIONTABLE_ENTRY(10b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(11b-linux_gateway_page, 30b-linux_gateway_page)

        /* A page fault occurred in critical region */
31:     b,n     lws_pagefault
        ASM_EXCEPTIONTABLE_ENTRY(12b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(13b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(14b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(15b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(16b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(17b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(18b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(19b-linux_gateway_page, 31b-linux_gateway_page)
#ifndef CONFIG_64BIT
        ASM_EXCEPTIONTABLE_ENTRY(20b-linux_gateway_page, 31b-linux_gateway_page)
#endif


        /***************************************************
                LWS atomic exchange.

                %r26 - Exchange address
                %r25 - Size of the variable (0/1/2/3 for 8/16/32/64 bit)
                %r24 - Address of new value
                %r23 - Address of old value
                %r28 - Return non-zero on failure
                %r21 - Kernel error code

                %r21 returns the following error codes:
                EAGAIN - CAS is busy, ldcw failed, try again.
                EFAULT - Read or write failed.

                If EAGAIN is returned, %r28 indicates the busy reason:
                r28 == 1 - CAS is busy. lock contended.
                r28 == 2 - CAS is busy. ldcw failed.
                r28 == 3 - CAS is busy. page fault.

                Scratch: r20, r1

        ****************************************************/

lws_atomic_xchg:
#ifdef CONFIG_64BIT
        /* Wide mode user process? */
        bb,<,n  %sp, 31, atomic_xchg_begin

        /* Clip the input registers for 32-bit processes. We don't
           need to clip %r23 as we only use it for word operations */
        depdi   0, 31, 32, %r26
        depdi   0, 31, 32, %r25
        depdi   0, 31, 32, %r24
        depdi   0, 31, 32, %r23
#endif

atomic_xchg_begin:
        /* Check the validity of the size pointer */
        subi,>>= 3, %r25, %r0
        b,n     lws_exit_nosys

        /* Jump to the functions which will load the old and new values into
           registers depending on the their size */
        shlw    %r25, 2, %r1
        blr     %r1, %r0
        nop

        /* Perform exception checks */

        /* 8-bit exchange */
1:      ldb     0(%r24), %r20
        proberi (%r24), PRIV_USER, %r20
        comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
        nop
        copy    %r23, %r20
        depi_safe       0, 31, 2, %r20
        b       atomic_xchg_start
2:      stbys,e %r0, 0(%r20)

        /* 16-bit exchange */
3:      ldh     0(%r24), %r20
        proberi (%r24), PRIV_USER, %r20
        comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
        nop
        copy    %r23, %r20
        depi_safe       0, 31, 2, %r20
        b       atomic_xchg_start
4:      stbys,e %r0, 0(%r20)

        /* 32-bit exchange */
5:      ldw     0(%r24), %r20
        proberi (%r24), PRIV_USER, %r20
        comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
        nop
        b       atomic_xchg_start
6:      stbys,e %r0, 0(%r23)
        nop
        nop

        /* 64-bit exchange */
#ifdef CONFIG_64BIT
7:      ldd     0(%r24), %r20
        proberi (%r24), PRIV_USER, %r20
        comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
        nop
8:      stdby,e %r0, 0(%r23)
#else
7:      ldw     0(%r24), %r20
8:      ldw     4(%r24), %r20
        proberi (%r24), PRIV_USER, %r20
        comb,=,n        %r20, %r0, lws_fault /* backwards, likely not taken */
        nop
        copy    %r23, %r20
        depi_safe       0, 31, 2, %r20
9:      stbys,e %r0, 0(%r20)
10:     stbys,e %r0, 4(%r20)
#endif

atomic_xchg_start:
        /* Trigger memory reference interruptions without writing to memory */
        copy    %r26, %r28
        depi_safe       0, 31, 2, %r28
11:     ldw     0(%r28), %r1
12:     stbys,e %r0, 0(%r28)

        /* Calculate 8-bit hash index from virtual address */
        extru_safe  %r26, 27, 8, %r20

        /* Load start of lock table */
        ldil    L%lws_lock_start, %r28
        ldo     R%lws_lock_start(%r28), %r28

        /* Find lock to use, the hash index is one of 0 to
           255, multiplied by 16 (keep it 16-byte aligned)
           and add to the lock table offset. */
        shlw    %r20, 4, %r20
        add     %r20, %r28, %r20

        rsm     PSW_SM_I, %r0                   /* Disable interrupts */

        /* Try to acquire the lock */
        LDCW    0(%sr2,%r20), %r28
        spinlock_check  %r28, %r21
        comclr,<>       %r0, %r28, %r0
        b,n     lws_wouldblock

        /* Disable page faults to prevent sleeping in critical region */
        lws_pagefault_disable   %r21,%r28

        /* NOTES:
                This all works because intr_do_signal
                and schedule both check the return iasq
                and see that we are on the kernel page
                so this process is never scheduled off
                or is ever sent any signal of any sort,
                thus it is wholly atomic from userspace's
                perspective
        */

        /* Jump to the correct function */
        blr     %r1, %r0
        /* Set %r28 as non-zero for now */
        ldo     1(%r0),%r28

        /* 8-bit exchange */
14:     ldb     0(%r26), %r1
15:     stb     %r1, 0(%r23)
15:     ldb     0(%r24), %r1
17:     stb     %r1, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28
        nop
        nop

        /* 16-bit exchange */
18:     ldh     0(%r26), %r1
19:     sth     %r1, 0(%r23)
20:     ldh     0(%r24), %r1
21:     sth     %r1, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28
        nop
        nop

        /* 32-bit exchange */
22:     ldw     0(%r26), %r1
23:     stw     %r1, 0(%r23)
24:     ldw     0(%r24), %r1
25:     stw     %r1, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28
        nop
        nop

        /* 64-bit exchange */
#ifdef CONFIG_64BIT
26:     ldd     0(%r26), %r1
27:     std     %r1, 0(%r23)
28:     ldd     0(%r24), %r1
29:     std     %r1, 0(%r26)
#else
26:     flddx   0(%r26), %fr4
27:     fstdx   %fr4, 0(%r23)
28:     flddx   0(%r24), %fr4
29:     fstdx   %fr4, 0(%r26)
#endif
        b       lws_exit_noerror
        copy    %r0, %r28

        /* A fault occurred on load or stbys,e store */
30:     b,n     lws_fault
        ASM_EXCEPTIONTABLE_ENTRY(1b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(2b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(3b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(4b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(5b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(6b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(7b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(8b-linux_gateway_page, 30b-linux_gateway_page)
#ifndef CONFIG_64BIT
        ASM_EXCEPTIONTABLE_ENTRY(9b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(10b-linux_gateway_page, 30b-linux_gateway_page)
#endif

        ASM_EXCEPTIONTABLE_ENTRY(11b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(12b-linux_gateway_page, 30b-linux_gateway_page)

        /* A page fault occurred in critical region */
31:     b,n     lws_pagefault
        ASM_EXCEPTIONTABLE_ENTRY(14b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(15b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(16b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(17b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(18b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(19b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(20b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(21b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(22b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(23b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(24b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(25b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(26b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(27b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(28b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(29b-linux_gateway_page, 31b-linux_gateway_page)

        /***************************************************
                LWS atomic store.

                %r26 - Address to store
                %r25 - Size of the variable (0/1/2/3 for 8/16/32/64 bit)
                %r24 - Address of value to store
                %r28 - Return non-zero on failure
                %r21 - Kernel error code

                %r21 returns the following error codes:
                EAGAIN - CAS is busy, ldcw failed, try again.
                EFAULT - Read or write failed.

                If EAGAIN is returned, %r28 indicates the busy reason:
                r28 == 1 - CAS is busy. lock contended.
                r28 == 2 - CAS is busy. ldcw failed.
                r28 == 3 - CAS is busy. page fault.

                Scratch: r20, r1

        ****************************************************/

lws_atomic_store:
#ifdef CONFIG_64BIT
        /* Wide mode user process? */
        bb,<,n  %sp, 31, atomic_store_begin

        /* Clip the input registers for 32-bit processes. We don't
           need to clip %r23 as we only use it for word operations */
        depdi   0, 31, 32, %r26
        depdi   0, 31, 32, %r25
        depdi   0, 31, 32, %r24
#endif

atomic_store_begin:
        /* Check the validity of the size pointer */
        subi,>>= 3, %r25, %r0
        b,n     lws_exit_nosys

        shlw    %r25, 1, %r1
        blr     %r1, %r0
        nop

        /* Perform exception checks */

        /* 8-bit store */
1:      ldb     0(%r24), %r20
        b,n     atomic_store_start
        nop
        nop

        /* 16-bit store */
2:      ldh     0(%r24), %r20
        b,n     atomic_store_start
        nop
        nop

        /* 32-bit store */
3:      ldw     0(%r24), %r20
        b,n     atomic_store_start
        nop
        nop

        /* 64-bit store */
#ifdef CONFIG_64BIT
4:      ldd     0(%r24), %r20
#else
4:      ldw     0(%r24), %r20
5:      ldw     4(%r24), %r20
#endif

atomic_store_start:
        /* Trigger memory reference interruptions without writing to memory */
        copy    %r26, %r28
        depi_safe       0, 31, 2, %r28
6:      ldw     0(%r28), %r1
7:      stbys,e %r0, 0(%r28)

        /* Calculate 8-bit hash index from virtual address */
        extru_safe  %r26, 27, 8, %r20

        /* Load start of lock table */
        ldil    L%lws_lock_start, %r28
        ldo     R%lws_lock_start(%r28), %r28

        /* Find lock to use, the hash index is one of 0 to
           255, multiplied by 16 (keep it 16-byte aligned)
           and add to the lock table offset. */
        shlw    %r20, 4, %r20
        add     %r20, %r28, %r20

        rsm     PSW_SM_I, %r0                   /* Disable interrupts */

        /* Try to acquire the lock */
        LDCW    0(%sr2,%r20), %r28
        spinlock_check  %r28, %r21
        comclr,<>       %r0, %r28, %r0
        b,n     lws_wouldblock

        /* Disable page faults to prevent sleeping in critical region */
        lws_pagefault_disable   %r21,%r28

        /* NOTES:
                This all works because intr_do_signal
                and schedule both check the return iasq
                and see that we are on the kernel page
                so this process is never scheduled off
                or is ever sent any signal of any sort,
                thus it is wholly atomic from userspace's
                perspective
        */

        /* Jump to the correct function */
        blr     %r1, %r0
        /* Set %r28 as non-zero for now */
        ldo     1(%r0),%r28

        /* 8-bit store */
9:      ldb     0(%r24), %r1
10:     stb     %r1, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28

        /* 16-bit store */
11:     ldh     0(%r24), %r1
12:     sth     %r1, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28

        /* 32-bit store */
13:     ldw     0(%r24), %r1
14:     stw     %r1, 0(%r26)
        b       lws_exit_noerror
        copy    %r0, %r28

        /* 64-bit store */
#ifdef CONFIG_64BIT
15:     ldd     0(%r24), %r1
16:     std     %r1, 0(%r26)
#else
15:     flddx   0(%r24), %fr4
16:     fstdx   %fr4, 0(%r26)
#endif
        b       lws_exit_noerror
        copy    %r0, %r28

        /* A fault occurred on load or stbys,e store */
30:     b,n     lws_fault
        ASM_EXCEPTIONTABLE_ENTRY(1b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(2b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(3b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(4b-linux_gateway_page, 30b-linux_gateway_page)
#ifndef CONFIG_64BIT
        ASM_EXCEPTIONTABLE_ENTRY(5b-linux_gateway_page, 30b-linux_gateway_page)
#endif

        ASM_EXCEPTIONTABLE_ENTRY(6b-linux_gateway_page, 30b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(7b-linux_gateway_page, 30b-linux_gateway_page)

        /* A page fault occurred in critical region */
31:     b,n     lws_pagefault
        ASM_EXCEPTIONTABLE_ENTRY(9b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(10b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(11b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(12b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(13b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(14b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(15b-linux_gateway_page, 31b-linux_gateway_page)
        ASM_EXCEPTIONTABLE_ENTRY(16b-linux_gateway_page, 31b-linux_gateway_page)

        /* Make sure nothing else is placed on this page */
        .align PAGE_SIZE
END(linux_gateway_page)
ENTRY(end_linux_gateway_page)

        /* Relocate symbols assuming linux_gateway_page is mapped
           to virtual address 0x0 */

#define LWS_ENTRY(_name_) ASM_ULONG_INSN (lws_##_name_ - linux_gateway_page)

        .section .rodata,"a"

        .align 8
        /* Light-weight-syscall table */
        /* Start of lws table. */
ENTRY(lws_table)
        LWS_ENTRY(compare_and_swap32)           /* 0 - ELF32 Atomic 32bit CAS */
        LWS_ENTRY(compare_and_swap64)           /* 1 - ELF64 Atomic 32bit CAS */
        LWS_ENTRY(compare_and_swap_2)           /* 2 - Atomic 64bit CAS */
        LWS_ENTRY(atomic_xchg)                  /* 3 - Atomic Exchange */
        LWS_ENTRY(atomic_store)                 /* 4 - Atomic Store */
END(lws_table)
        /* End of lws table */

#ifdef CONFIG_64BIT
#define __SYSCALL_WITH_COMPAT(nr, native, compat)       __SYSCALL(nr, compat)
#else
#define __SYSCALL_WITH_COMPAT(nr, native, compat)       __SYSCALL(nr, native)
#endif
#define __SYSCALL(nr, entry)    ASM_ULONG_INSN entry
        .align 8
ENTRY(sys_call_table)
        .export sys_call_table,data
#include <asm/syscall_table_32.h>    /* 32-bit syscalls */
END(sys_call_table)

#ifdef CONFIG_64BIT
#undef __SYSCALL_WITH_COMPAT
#define __SYSCALL_WITH_COMPAT(nr, native, compat)       __SYSCALL(nr, native)
        .align 8
ENTRY(sys_call_table64)
#include <asm/syscall_table_64.h>    /* 64-bit syscalls */
END(sys_call_table64)
#endif

        /*
                All light-weight-syscall atomic operations 
                will use this set of locks 

                NOTE: The lws_lock_start symbol must be
                at least 16-byte aligned for safe use
                with ldcw.
        */
        .section .data
        .align  L1_CACHE_BYTES
ENTRY(lws_lock_start)
        /* lws locks */
        .rept 256
        /* Keep locks aligned at 16-bytes */
        .word __ARCH_SPIN_LOCK_UNLOCKED_VAL
        .word 0 
        .word 0
        .word 0
        .endr
END(lws_lock_start)
        .previous

.end