arch/parisc/kernel/syscall.S

   1 /*
   2  * Linux/PA-RISC Project (http://www.parisc-linux.org/)
   3  *
   4  * System call entry code Copyright (c) Matthew Wilcox 1999 <willy@bofh.ai>
   5  * Licensed under the GNU GPL.
   6  * thanks to Philipp Rumpf, Mike Shaver and various others
   7  * sorry about the wall, puffin..
   8  */
   9
  10 #include <asm/asm-offsets.h>
  11 #include <asm/unistd.h>
  12 #include <asm/errno.h>
  13 #include <asm/page.h>
  14 #include <asm/psw.h>
  15 #include <asm/thread_info.h>
  16 #include <asm/assembly.h>
  17 #include <asm/processor.h>
  18
  19 #include <linux/linkage.h>
  20
  21         /* We fill the empty parts of the gateway page with
  22          * something that will kill the kernel or a
  23          * userspace application.
  24          */
  25 #define KILL_INSN       break   0,0
  26
  27         .level          LEVEL
  28
  29         .text
  30
  31         .import syscall_exit,code
  32         .import syscall_exit_rfi,code
  33
  34         /* Linux gateway page is aliased to virtual page 0 in the kernel
  35          * address space. Since it is a gateway page it cannot be
  36          * dereferenced, so null pointers will still fault. We start
  37          * the actual entry point at 0x100. We put break instructions
  38          * at the beginning of the page to trap null indirect function
  39          * pointers.
  40          */
  41
  42         .align PAGE_SIZE
  43 ENTRY(linux_gateway_page)
  44
  45         /* ADDRESS 0x00 to 0xb0 = 176 bytes / 4 bytes per insn = 44 insns */
  46         .rept 44
  47         KILL_INSN
  48         .endr
  49
  50         /* ADDRESS 0xb0 to 0xb8, lws uses two insns for entry */
  51         /* Light-weight-syscall entry must always be located at 0xb0 */
  52         /* WARNING: Keep this number updated with table size changes */
  53 #define __NR_lws_entries (2)
  54
  55 lws_entry:
  56         gate    lws_start, %r0          /* increase privilege */
  57         depi    3, 31, 2, %r31          /* Ensure we return into user mode. */
  58
  59         /* Fill from 0xb8 to 0xe0 */
  60         .rept 10
  61         KILL_INSN
  62         .endr
  63
  64         /* This function MUST be located at 0xe0 for glibc's threading
  65         mechanism to work. DO NOT MOVE THIS CODE EVER! */
  66 set_thread_pointer:
  67         gate    .+8, %r0                /* increase privilege */
  68         depi    3, 31, 2, %r31          /* Ensure we return into user mode. */
  69         be      0(%sr7,%r31)            /* return to user space */
  70         mtctl   %r26, %cr27             /* move arg0 to the control register */
  71
  72         /* Increase the chance of trapping if random jumps occur to this
  73         address, fill from 0xf0 to 0x100 */
  74         .rept 4
  75         KILL_INSN
  76         .endr
  77
  78 /* This address must remain fixed at 0x100 for glibc's syscalls to work */
  79         .align 256
  80 linux_gateway_entry:
  81         gate    .+8, %r0                        /* become privileged */
  82         mtsp    %r0,%sr4                        /* get kernel space into sr4 */
  83         mtsp    %r0,%sr5                        /* get kernel space into sr5 */
  84         mtsp    %r0,%sr6                        /* get kernel space into sr6 */
  85         mfsp    %sr7,%r1                        /* save user sr7 */
  86         mtsp    %r1,%sr3                        /* and store it in sr3 */
  87
  88 #ifdef CONFIG_64BIT
  89         /* for now we can *always* set the W bit on entry to the syscall
  90          * since we don't support wide userland processes.  We could
  91          * also save the current SM other than in r0 and restore it on
  92          * exit from the syscall, and also use that value to know
  93          * whether to do narrow or wide syscalls. -PB
  94          */
  95         ssm     PSW_SM_W, %r1
  96         extrd,u %r1,PSW_W_BIT,1,%r1
  97         /* sp must be aligned on 4, so deposit the W bit setting into
  98          * the bottom of sp temporarily */
  99         or,ev   %r1,%r30,%r30
 100         b,n     1f
 101         /* The top halves of argument registers must be cleared on syscall
 102          * entry from narrow executable.
 103          */
 104         depdi   0, 31, 32, %r26
 105         depdi   0, 31, 32, %r25
 106         depdi   0, 31, 32, %r24
 107         depdi   0, 31, 32, %r23
 108         depdi   0, 31, 32, %r22
 109         depdi   0, 31, 32, %r21
 110 1:
 111 #endif
 112         mfctl   %cr30,%r1
 113         xor     %r1,%r30,%r30                   /* ye olde xor trick */
 114         xor     %r1,%r30,%r1
 115         xor     %r1,%r30,%r30
 116
 117         ldo     THREAD_SZ_ALGN+FRAME_SIZE(%r30),%r30  /* set up kernel stack */
 118
 119         /* N.B.: It is critical that we don't set sr7 to 0 until r30
 120          *       contains a valid kernel stack pointer. It is also
 121          *       critical that we don't start using the kernel stack
 122          *       until after sr7 has been set to 0.
 123          */
 124
 125         mtsp    %r0,%sr7                        /* get kernel space into sr7 */
 126         STREGM  %r1,FRAME_SIZE(%r30)            /* save r1 (usp) here for now */
 127         mfctl   %cr30,%r1                       /* get task ptr in %r1 */
 128         LDREG   TI_TASK(%r1),%r1
 129
 130         /* Save some registers for sigcontext and potential task
 131            switch (see entry.S for the details of which ones are
 132            saved/restored).  TASK_PT_PSW is zeroed so we can see whether
 133            a process is on a syscall or not.  For an interrupt the real
 134            PSW value is stored.  This is needed for gdb and sys_ptrace. */
 135         STREG   %r0,  TASK_PT_PSW(%r1)
 136         STREG   %r2,  TASK_PT_GR2(%r1)          /* preserve rp */
 137         STREG   %r19, TASK_PT_GR19(%r1)
 138
 139         LDREGM  -FRAME_SIZE(%r30), %r2          /* get users sp back */
 140 #ifdef CONFIG_64BIT
 141         extrd,u %r2,63,1,%r19                   /* W hidden in bottom bit */
 142 #if 0
 143         xor     %r19,%r2,%r2                    /* clear bottom bit */
 144         depd,z  %r19,1,1,%r19
 145         std     %r19,TASK_PT_PSW(%r1)
 146 #endif
 147 #endif
 148         STREG   %r2,  TASK_PT_GR30(%r1)         /* ... and save it */
 149
 150         STREG   %r20, TASK_PT_GR20(%r1)         /* Syscall number */
 151         STREG   %r21, TASK_PT_GR21(%r1)
 152         STREG   %r22, TASK_PT_GR22(%r1)
 153         STREG   %r23, TASK_PT_GR23(%r1)         /* 4th argument */
 154         STREG   %r24, TASK_PT_GR24(%r1)         /* 3rd argument */
 155         STREG   %r25, TASK_PT_GR25(%r1)         /* 2nd argument */
 156         STREG   %r26, TASK_PT_GR26(%r1)         /* 1st argument */
 157         STREG   %r27, TASK_PT_GR27(%r1)         /* user dp */
 158         STREG   %r28, TASK_PT_GR28(%r1)         /* return value 0 */
 159         STREG   %r28, TASK_PT_ORIG_R28(%r1)     /* return value 0 (saved for signals) */
 160         STREG   %r29, TASK_PT_GR29(%r1)         /* return value 1 */
 161         STREG   %r31, TASK_PT_GR31(%r1)         /* preserve syscall return ptr */
 162
 163         ldo     TASK_PT_FR0(%r1), %r27          /* save fpregs from the kernel */
 164         save_fp %r27                            /* or potential task switch  */
 165
 166         mfctl   %cr11, %r27                     /* i.e. SAR */
 167         STREG   %r27, TASK_PT_SAR(%r1)
 168
 169         loadgp
 170
 171 #ifdef CONFIG_64BIT
 172         ldo     -16(%r30),%r29                  /* Reference param save area */
 173         copy    %r19,%r2                        /* W bit back to r2 */
 174 #else
 175         /* no need to save these on stack in wide mode because the first 8
 176          * args are passed in registers */
 177         stw     %r22, -52(%r30)                 /* 5th argument */
 178         stw     %r21, -56(%r30)                 /* 6th argument */
 179 #endif
 180
 181         /* Are we being ptraced? */
 182         mfctl   %cr30, %r1
 183         LDREG   TI_TASK(%r1),%r1
 184         ldw     TASK_PTRACE(%r1), %r1
 185         bb,<,n  %r1,31,.Ltracesys
 186
 187         /* Note!  We cannot use the syscall table that is mapped
 188         nearby since the gateway page is mapped execute-only. */
 189
 190 #ifdef CONFIG_64BIT
 191         ldil    L%sys_call_table, %r1
 192         or,=    %r2,%r2,%r2
 193         addil   L%(sys_call_table64-sys_call_table), %r1
 194         ldo     R%sys_call_table(%r1), %r19
 195         or,=    %r2,%r2,%r2
 196         ldo     R%sys_call_table64(%r1), %r19
 197 #else
 198         ldil    L%sys_call_table, %r1
 199         ldo     R%sys_call_table(%r1), %r19
 200 #endif
 201         comiclr,>>      __NR_Linux_syscalls, %r20, %r0
 202         b,n     .Lsyscall_nosys
 203
 204         LDREGX  %r20(%r19), %r19
 205
 206         /* If this is a sys_rt_sigreturn call, and the signal was received
 207          * when not in_syscall, then we want to return via syscall_exit_rfi,
 208          * not syscall_exit.  Signal no. in r20, in_syscall in r25 (see
 209          * trampoline code in signal.c).
 210          */
 211         ldi     __NR_rt_sigreturn,%r2
 212         comb,=  %r2,%r20,.Lrt_sigreturn
 213 .Lin_syscall:
 214         ldil    L%syscall_exit,%r2
 215         be      0(%sr7,%r19)
 216         ldo     R%syscall_exit(%r2),%r2
 217 .Lrt_sigreturn:
 218         comib,<> 0,%r25,.Lin_syscall
 219         ldil    L%syscall_exit_rfi,%r2
 220         be      0(%sr7,%r19)
 221         ldo     R%syscall_exit_rfi(%r2),%r2
 222
 223         /* Note!  Because we are not running where we were linked, any
 224         calls to functions external to this file must be indirect.  To
 225         be safe, we apply the opposite rule to functions within this
 226         file, with local labels given to them to ensure correctness. */
 227
 228 .Lsyscall_nosys:
 229 syscall_nosys:
 230         ldil    L%syscall_exit,%r1
 231         be      R%syscall_exit(%sr7,%r1)
 232         ldo     -ENOSYS(%r0),%r28                  /* set errno */
 233
 234
 235 /* Warning! This trace code is a virtual duplicate of the code above so be
 236  * sure to maintain both! */
 237 .Ltracesys:
 238 tracesys:
 239         /* Need to save more registers so the debugger can see where we
 240          * are.  This saves only the lower 8 bits of PSW, so that the C
 241          * bit is still clear on syscalls, and the D bit is set if this
 242          * full register save path has been executed.  We check the D
 243          * bit on syscall_return_rfi to determine which registers to
 244          * restore.  An interrupt results in a full PSW saved with the
 245          * C bit set, a non-straced syscall entry results in C and D clear
 246          * in the saved PSW.
 247          */
 248         ldo     -THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1      /* get task ptr */
 249         LDREG   TI_TASK(%r1), %r1
 250         ssm     0,%r2
 251         STREG   %r2,TASK_PT_PSW(%r1)            /* Lower 8 bits only!! */
 252         mfsp    %sr0,%r2
 253         STREG   %r2,TASK_PT_SR0(%r1)
 254         mfsp    %sr1,%r2
 255         STREG   %r2,TASK_PT_SR1(%r1)
 256         mfsp    %sr2,%r2
 257         STREG   %r2,TASK_PT_SR2(%r1)
 258         mfsp    %sr3,%r2
 259         STREG   %r2,TASK_PT_SR3(%r1)
 260         STREG   %r2,TASK_PT_SR4(%r1)
 261         STREG   %r2,TASK_PT_SR5(%r1)
 262         STREG   %r2,TASK_PT_SR6(%r1)
 263         STREG   %r2,TASK_PT_SR7(%r1)
 264         STREG   %r2,TASK_PT_IASQ0(%r1)
 265         STREG   %r2,TASK_PT_IASQ1(%r1)
 266         LDREG   TASK_PT_GR31(%r1),%r2
 267         STREG   %r2,TASK_PT_IAOQ0(%r1)
 268         ldo     4(%r2),%r2
 269         STREG   %r2,TASK_PT_IAOQ1(%r1)
 270         ldo     TASK_REGS(%r1),%r2
 271         /* reg_save %r2 */
 272         STREG   %r3,PT_GR3(%r2)
 273         STREG   %r4,PT_GR4(%r2)
 274         STREG   %r5,PT_GR5(%r2)
 275         STREG   %r6,PT_GR6(%r2)
 276         STREG   %r7,PT_GR7(%r2)
 277         STREG   %r8,PT_GR8(%r2)
 278         STREG   %r9,PT_GR9(%r2)
 279         STREG   %r10,PT_GR10(%r2)
 280         STREG   %r11,PT_GR11(%r2)
 281         STREG   %r12,PT_GR12(%r2)
 282         STREG   %r13,PT_GR13(%r2)
 283         STREG   %r14,PT_GR14(%r2)
 284         STREG   %r15,PT_GR15(%r2)
 285         STREG   %r16,PT_GR16(%r2)
 286         STREG   %r17,PT_GR17(%r2)
 287         STREG   %r18,PT_GR18(%r2)
 288         /* Finished saving things for the debugger */
 289
 290         copy    %r2,%r26
 291         ldil    L%do_syscall_trace_enter,%r1
 292         ldil    L%tracesys_next,%r2
 293         be      R%do_syscall_trace_enter(%sr7,%r1)
 294         ldo     R%tracesys_next(%r2),%r2
 295
 296 tracesys_next:
 297         /* do_syscall_trace_enter either returned the syscallno, or -1L,
 298          *  so we skip restoring the PT_GR20 below, since we pulled it from
 299          *  task->thread.regs.gr[20] above.
 300          */
 301         copy    %ret0,%r20
 302         ldil    L%sys_call_table,%r1
 303         ldo     R%sys_call_table(%r1), %r19
 304
 305         ldo     -THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1      /* get task ptr */
 306         LDREG   TI_TASK(%r1), %r1
 307         LDREG   TASK_PT_GR26(%r1), %r26         /* Restore the users args */
 308         LDREG   TASK_PT_GR25(%r1), %r25
 309         LDREG   TASK_PT_GR24(%r1), %r24
 310         LDREG   TASK_PT_GR23(%r1), %r23
 311 #ifdef CONFIG_64BIT
 312         LDREG   TASK_PT_GR22(%r1), %r22
 313         LDREG   TASK_PT_GR21(%r1), %r21
 314         ldo     -16(%r30),%r29                  /* Reference param save area */
 315 #endif
 316
 317         comiclr,>>=     __NR_Linux_syscalls, %r20, %r0
 318         b,n     .Lsyscall_nosys
 319
 320         LDREGX  %r20(%r19), %r19
 321
 322         /* If this is a sys_rt_sigreturn call, and the signal was received
 323          * when not in_syscall, then we want to return via syscall_exit_rfi,
 324          * not syscall_exit.  Signal no. in r20, in_syscall in r25 (see
 325          * trampoline code in signal.c).
 326          */
 327         ldi     __NR_rt_sigreturn,%r2
 328         comb,=  %r2,%r20,.Ltrace_rt_sigreturn
 329 .Ltrace_in_syscall:
 330         ldil    L%tracesys_exit,%r2
 331         be      0(%sr7,%r19)
 332         ldo     R%tracesys_exit(%r2),%r2
 333
 334         /* Do *not* call this function on the gateway page, because it
 335         makes a direct call to syscall_trace. */
 336
 337 tracesys_exit:
 338         ldo     -THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1      /* get task ptr */
 339         LDREG   TI_TASK(%r1), %r1
 340 #ifdef CONFIG_64BIT
 341         ldo     -16(%r30),%r29                  /* Reference param save area */
 342 #endif
 343         ldo     TASK_REGS(%r1),%r26
 344         bl      do_syscall_trace_exit,%r2
 345         STREG   %r28,TASK_PT_GR28(%r1)          /* save return value now */
 346         ldo     -THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1      /* get task ptr */
 347         LDREG   TI_TASK(%r1), %r1
 348         LDREG   TASK_PT_GR28(%r1), %r28         /* Restore return val. */
 349
 350         ldil    L%syscall_exit,%r1
 351         be,n    R%syscall_exit(%sr7,%r1)
 352
 353 .Ltrace_rt_sigreturn:
 354         comib,<> 0,%r25,.Ltrace_in_syscall
 355         ldil    L%tracesys_sigexit,%r2
 356         be      0(%sr7,%r19)
 357         ldo     R%tracesys_sigexit(%r2),%r2
 358
 359 tracesys_sigexit:
 360         ldo     -THREAD_SZ_ALGN-FRAME_SIZE(%r30),%r1      /* get task ptr */
 361         LDREG   TI_TASK(%r1), %r1
 362 #ifdef CONFIG_64BIT
 363         ldo     -16(%r30),%r29                  /* Reference param save area */
 364 #endif
 365         bl      do_syscall_trace_exit,%r2
 366         ldo     TASK_REGS(%r1),%r26
 367
 368         ldil    L%syscall_exit_rfi,%r1
 369         be,n    R%syscall_exit_rfi(%sr7,%r1)
 370
 371
 372         /*********************************************************
 373                 32/64-bit Light-Weight-Syscall ABI
 374
 375                 * - Indicates a hint for userspace inline asm
 376                 implementations.
 377
 378                 Syscall number (caller-saves)
 379                 - %r20
 380                 * In asm clobber.
 381
 382                 Argument registers (caller-saves)
 383                 - %r26, %r25, %r24, %r23, %r22
 384                 * In asm input.
 385
 386                 Return registers (caller-saves)
 387                 - %r28 (return), %r21 (errno)
 388                 * In asm output.
 389
 390                 Caller-saves registers
 391                 - %r1, %r27, %r29
 392                 - %r2 (return pointer)
 393                 - %r31 (ble link register)
 394                 * In asm clobber.
 395
 396                 Callee-saves registers
 397                 - %r3-%r18
 398                 - %r30 (stack pointer)
 399                 * Not in asm clobber.
 400
 401                 If userspace is 32-bit:
 402                 Callee-saves registers
 403                 - %r19 (32-bit PIC register)
 404
 405                 Differences from 32-bit calling convention:
 406                 - Syscall number in %r20
 407                 - Additional argument register %r22 (arg4)
 408                 - Callee-saves %r19.
 409
 410                 If userspace is 64-bit:
 411                 Callee-saves registers
 412                 - %r27 (64-bit PIC register)
 413
 414                 Differences from 64-bit calling convention:
 415                 - Syscall number in %r20
 416                 - Additional argument register %r22 (arg4)
 417                 - Callee-saves %r27.
 418
 419                 Error codes returned by entry path:
 420
 421                 ENOSYS - r20 was an invalid LWS number.
 422
 423         *********************************************************/
 424 lws_start:
 425
 426 #ifdef CONFIG_64BIT
 427         /* FIXME: If we are a 64-bit kernel just
 428          *        turn this on unconditionally.
 429          */
 430         ssm     PSW_SM_W, %r1
 431         extrd,u %r1,PSW_W_BIT,1,%r1
 432         /* sp must be aligned on 4, so deposit the W bit setting into
 433          * the bottom of sp temporarily */
 434         or,ev   %r1,%r30,%r30
 435
 436         /* Clip LWS number to a 32-bit value always */
 437         depdi   0, 31, 32, %r20
 438 #endif
 439
 440         /* Is the lws entry number valid? */
 441         comiclr,>>      __NR_lws_entries, %r20, %r0
 442         b,n     lws_exit_nosys
 443
 444         /* WARNING: Trashing sr2 and sr3 */
 445         mfsp    %sr7,%r1                        /* get userspace into sr3 */
 446         mtsp    %r1,%sr3
 447         mtsp    %r0,%sr2                        /* get kernel space into sr2 */
 448
 449         /* Load table start */
 450         ldil    L%lws_table, %r1
 451         ldo     R%lws_table(%r1), %r28  /* Scratch use of r28 */
 452         LDREGX  %r20(%sr2,r28), %r21    /* Scratch use of r21 */
 453
 454         /* Jump to lws, lws table pointers already relocated */
 455         be,n    0(%sr2,%r21)
 456
 457 lws_exit_nosys:
 458         ldo     -ENOSYS(%r0),%r21                  /* set errno */
 459         /* Fall through: Return to userspace */
 460
 461 lws_exit:
 462 #ifdef CONFIG_64BIT
 463         /* decide whether to reset the wide mode bit
 464          *
 465          * For a syscall, the W bit is stored in the lowest bit
 466          * of sp.  Extract it and reset W if it is zero */
 467         extrd,u,*<>     %r30,63,1,%r1
 468         rsm     PSW_SM_W, %r0
 469         /* now reset the lowest bit of sp if it was set */
 470         xor     %r30,%r1,%r30
 471 #endif
 472         be,n    0(%sr7, %r31)
 473
 474
 475
 476         /***************************************************
 477                 Implementing CAS as an atomic operation:
 478
 479                 %r26 - Address to examine
 480                 %r25 - Old value to check (old)
 481                 %r24 - New value to set (new)
 482                 %r28 - Return prev through this register.
 483                 %r21 - Kernel error code
 484
 485                 If debugging is DISabled:
 486
 487                 %r21 has the following meanings:
 488
 489                 EAGAIN - CAS is busy, ldcw failed, try again.
 490                 EFAULT - Read or write failed.
 491
 492                 If debugging is enabled:
 493
 494                 EDEADLOCK - CAS called recursively.
 495                 EAGAIN && r28 == 1 - CAS is busy. Lock contended.
 496                 EAGAIN && r28 == 2 - CAS is busy. ldcw failed.
 497                 EFAULT - Read or write failed.
 498
 499                 Scratch: r20, r28, r1
 500
 501         ****************************************************/
 502
 503         /* Do not enable LWS debugging */
 504 #define ENABLE_LWS_DEBUG 0
 505
 506         /* ELF64 Process entry path */
 507 lws_compare_and_swap64:
 508 #ifdef CONFIG_64BIT
 509         b,n     lws_compare_and_swap
 510 #else
 511         /* If we are not a 64-bit kernel, then we don't
 512          * have 64-bit input registers, and calling
 513          * the 64-bit LWS CAS returns ENOSYS.
 514          */
 515         b,n     lws_exit_nosys
 516 #endif
 517
 518         /* ELF32 Process entry path */
 519 lws_compare_and_swap32:
 520 #ifdef CONFIG_64BIT
 521         /* Clip all the input registers */
 522         depdi   0, 31, 32, %r26
 523         depdi   0, 31, 32, %r25
 524         depdi   0, 31, 32, %r24
 525 #endif
 526
 527 lws_compare_and_swap:
 528         /* Load start of lock table */
 529         ldil    L%lws_lock_start, %r20
 530         ldo     R%lws_lock_start(%r20), %r28
 531
 532         /* Extract four bits from r26 and hash lock (Bits 4-7) */
 533         extru  %r26, 27, 4, %r20
 534
 535         /* Find lock to use, the hash is either one of 0 to
 536            15, multiplied by 16 (keep it 16-byte aligned)
 537            and add to the lock table offset. */
 538         shlw    %r20, 4, %r20
 539         add     %r20, %r28, %r20
 540
 541 # if ENABLE_LWS_DEBUG
 542         /*
 543                 DEBUG, check for deadlock!
 544                 If the thread register values are the same
 545                 then we were the one that locked it last and
 546                 this is a recurisve call that will deadlock.
 547                 We *must* giveup this call and fail.
 548         */
 549         ldw     4(%sr2,%r20), %r28                      /* Load thread register */
 550         /* WARNING: If cr27 cycles to the same value we have problems */
 551         mfctl   %cr27, %r21                             /* Get current thread register */
 552         cmpb,<>,n       %r21, %r28, cas_lock            /* Called recursive? */
 553         b       lws_exit                                /* Return error! */
 554         ldo     -EDEADLOCK(%r0), %r21
 555 cas_lock:
 556         cmpb,=,n        %r0, %r28, cas_nocontend        /* Is nobody using it? */
 557         ldo     1(%r0), %r28                            /* 1st case */
 558         b       lws_exit                                /* Contended... */
 559         ldo     -EAGAIN(%r0), %r21                      /* Spin in userspace */
 560 cas_nocontend:
 561 # endif
 562 /* ENABLE_LWS_DEBUG */
 563
 564         LDCW    0(%sr2,%r20), %r28                      /* Try to acquire the lock */
 565         cmpb,<>,n       %r0, %r28, cas_action           /* Did we get it? */
 566 cas_wouldblock:
 567         ldo     2(%r0), %r28                            /* 2nd case */
 568         b       lws_exit                                /* Contended... */
 569         ldo     -EAGAIN(%r0), %r21                      /* Spin in userspace */
 570
 571         /*
 572                 prev = *addr;
 573                 if ( prev == old )
 574                   *addr = new;
 575                 return prev;
 576         */
 577
 578         /* NOTES:
 579                 This all works becuse intr_do_signal
 580                 and schedule both check the return iasq
 581                 and see that we are on the kernel page
 582                 so this process is never scheduled off
 583                 or is ever sent any signal of any sort,
 584                 thus it is wholly atomic from usrspaces
 585                 perspective
 586         */
 587 cas_action:
 588 #if defined CONFIG_SMP && ENABLE_LWS_DEBUG
 589         /* DEBUG */
 590         mfctl   %cr27, %r1
 591         stw     %r1, 4(%sr2,%r20)
 592 #endif
 593         /* The load and store could fail */
 594 1:      ldw     0(%sr3,%r26), %r28
 595         sub,<>  %r28, %r25, %r0
 596 2:      stw     %r24, 0(%sr3,%r26)
 597         /* Free lock */
 598         stw     %r20, 0(%sr2,%r20)
 599 #if ENABLE_LWS_DEBUG
 600         /* Clear thread register indicator */
 601         stw     %r0, 4(%sr2,%r20)
 602 #endif
 603         /* Return to userspace, set no error */
 604         b       lws_exit
 605         copy    %r0, %r21
 606
 607 3:
 608         /* Error occurred on load or store */
 609         /* Free lock */
 610         stw     %r20, 0(%sr2,%r20)
 611 #if ENABLE_LWS_DEBUG
 612         stw     %r0, 4(%sr2,%r20)
 613 #endif
 614         b       lws_exit
 615         ldo     -EFAULT(%r0),%r21       /* set errno */
 616         nop
 617         nop
 618         nop
 619         nop
 620
 621         /* Two exception table entries, one for the load,
 622            the other for the store. Either return -EFAULT.
 623            Each of the entries must be relocated. */
 624         .section __ex_table,"aw"
 625         ASM_ULONG_INSN (1b - linux_gateway_page), (3b - linux_gateway_page)
 626         ASM_ULONG_INSN (2b - linux_gateway_page), (3b - linux_gateway_page)
 627         .previous
 628
 629
 630         /* Make sure nothing else is placed on this page */
 631         .align PAGE_SIZE
 632 END(linux_gateway_page)
 633 ENTRY(end_linux_gateway_page)
 634
 635         /* Relocate symbols assuming linux_gateway_page is mapped
 636            to virtual address 0x0 */
 637
 638 #define LWS_ENTRY(_name_) ASM_ULONG_INSN (lws_##_name_ - linux_gateway_page)
 639
 640         .section .rodata,"a"
 641
 642         .align PAGE_SIZE
 643         /* Light-weight-syscall table */
 644         /* Start of lws table. */
 645 ENTRY(lws_table)
 646         LWS_ENTRY(compare_and_swap32)   /* 0 - ELF32 Atomic compare and swap */
 647         LWS_ENTRY(compare_and_swap64)   /* 1 - ELF64 Atomic compare and swap */
 648 END(lws_table)
 649         /* End of lws table */
 650
 651         .align PAGE_SIZE
 652 ENTRY(sys_call_table)
 653 #include "syscall_table.S"
 654 END(sys_call_table)
 655
 656 #ifdef CONFIG_64BIT
 657         .align PAGE_SIZE
 658 ENTRY(sys_call_table64)
 659 #define SYSCALL_TABLE_64BIT
 660 #include "syscall_table.S"
 661 END(sys_call_table64)
 662 #endif
 663
 664         /*
 665                 All light-weight-syscall atomic operations
 666                 will use this set of locks
 667
 668                 NOTE: The lws_lock_start symbol must be
 669                 at least 16-byte aligned for safe use
 670                 with ldcw.
 671         */
 672         .section .data
 673         .align  PAGE_SIZE
 674 ENTRY(lws_lock_start)
 675         /* lws locks */
 676         .rept 16
 677         /* Keep locks aligned at 16-bytes */
 678         .word 1
 679         .word 0
 680         .word 0
 681         .word 0
 682         .endr
 683 END(lws_lock_start)
 684         .previous
 685
 686 .end
 687
 688