+++ /dev/null
-/* exc-syscall-handler.S - XTOS syscall instruction handler */
-
-/*
- * Copyright (c) 1999-2010 Tensilica Inc.
- *
- * Permission is hereby granted, free of charge, to any person obtaining
- * a copy of this software and associated documentation files (the
- * "Software"), to deal in the Software without restriction, including
- * without limitation the rights to use, copy, modify, merge, publish,
- * distribute, sublicense, and/or sell copies of the Software, and to
- * permit persons to whom the Software is furnished to do so, subject to
- * the following conditions:
- *
- * The above copyright notice and this permission notice shall be included
- * in all copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
- * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
- * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
- * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
- * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
- * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
- * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
- */
-
-/*
- * The SYSCALL instruction is typically used to implement system calls.
- * By convention, register a2 identifies the requested system call.
- * Typically, other parameters are passed in registers a3 and up,
- * and results are returned in a2.
- *
- * The Xtensa windowed ABI reserves the value zero of register a2
- * as a request to force register windows to the stack. The call0 ABI,
- * which has no equivalent operation, reserves this value as a no-op.
- *
- * Generally, only code that traverses the stack in unusual ways needs
- * to force (spill) register windows to the stack. In generic C or C++,
- * there are four cases, and they all use the standard SYSCALL mechanism:
- *
- * 1. C++ exceptions
- * 2. setjmp and longjmp
- * 3. functions using the GNU extension "__builtin_return_address"
- * 4. functions using the GNU extension "nonlocal goto"
- *
- * NOTE: Specific operating systems often need to spill register windows
- * to the stack in other situations such as context-switching, passing
- * Unix-like signals to threads, displaying stack tracebacks, etc.
- * They may choose to use the SYSCALL mechanism to do so, or use other
- * means such as calling xthal_window_spill() or other methods.
- *
- * If you want to handle other system calls, you can modify this file, or
- * use the C version of it in exc-syscall-handler.c . The Xtensa ABIs only
- * define system call zero; the behavior of other system calls is up to you.
- */
-
-#include <xtensa/coreasm.h>
-#include "xtos-internal.h"
-
-
-#if XCHAL_HAVE_EXCEPTIONS
-
-//Vector:
-// addi a1, a1, -ESF_TOTALSIZE // allocate exception stack frame, etc.
-// s32i a2, a1, UEXC_a2
-// s32i a3, a1, UEXC_a3
-// movi a3, _xtos_exc_handler_table
-// rsr a2, EXCCAUSE
-// addx4 a2, a2, a3
-// l32i a2, a2, 0
-// s32i a4, a1, UEXC_a4
-// jx a2 // jump to cause-specific handler
-
- .global _need_user_vector_ // pull-in real user vector (tiny LSP)
-
-
- /*
- * The SYSCALL handler is entered when the processor
- * executes the SYSCALL instruction.
- * By convention, the system call to execute is specified in a2.
- */
- .text
- .align 4
- .global _xtos_syscall_handler
-_xtos_syscall_handler:
- // HERE: a2, a3, a4 have been saved to the exception stack frame allocated with a1 (sp).
- // We ignore that a4 was saved, we don't clobber it.
-
- rsr a3, EPC_1
-#if XCHAL_HAVE_LOOPS
- // If the SYSCALL instruction was the last instruction in the body of
- // a zero-overhead loop, and the loop will execute again, decrement
- // the loop count and resume execution at the head of the loop:
- //
- rsr a2, LEND
- addi a3, a3, 3 // increment EPC to skip the SYSCALL instruction
- bne a2, a3, 1f
- rsr a2, LCOUNT
- beqz a2, 1f
- addi a2, a2, -1
- wsr a2, LCOUNT
- rsr a3, LBEG
-1: l32i a2, a1, UEXC_a2 // get the system call number
-#else
- // No loop registers.
- l32i a2, a1, UEXC_a2 // get the system call number
- addi a3, a3, 3 // increment EPC to skip the SYSCALL instruction
-#endif
- wsr a3, EPC_1 // update EPC1 past SYSCALL
- l32i a3, a1, UEXC_a3 // restore a3
- // If you want to handle other system calls, check a2 here.
-
-#ifdef __XTENSA_WINDOWED_ABI__
- bnez a2, .Lnotzero // is syscall number zero?
-
- /* Spill register windows to the stack. */
-
- // Save a2 thru a5 in the nested-C-function area, where an interrupt
- // won't clobber them. The pseudo-CALL's ENTRY below clobbers a4 and a5.
- //s32i a2, a1, (ESF_TOTALSIZE - 32) + 0 // a2 is zero, no need to save
- s32i a3, a1, (ESF_TOTALSIZE - 32) + 4
- s32i a4, a1, (ESF_TOTALSIZE - 32) + 8
- s32i a5, a1, (ESF_TOTALSIZE - 32) + 12
-
- movi a3, PS_WOE|PS_CALLINC(1)|PS_UM|PS_INTLEVEL(XCHAL_EXCM_LEVEL) // CALL4 emulation
- rsr a2, PS // save PS in a2
- wsr a3, PS // PS.INTLEVEL=EXCMLEVEL (1 for XEA1)
- // HERE: window overflows enabled but NOT SAFE yet, touch only a0..a3 until it's safe.
- rsr a3, EPC_1 // save EPC1 in a3
- addi a1, a1, ESF_TOTALSIZE // restore sp (dealloc ESF) for sane stack again
- rsync // wait for WSR to PS to complete
- // HERE: Window overflows and interrupts are safe, we saved EPC1 and
- // restored a1, and a4-a15 are unmodified.
- // Pseudo-CALL: make it look as if the code that executed SYSCALL
- // made a CALL4 to here. See user exc. handler comments for details.
- // ENTRY cannot cause window overflow; touch a4 to ensure a4-a7
- // overflow if needed:
- movi a4, 0 // clears pseudo-CALL's return PC
- // NOTE: On XEA1 processors, return from window overflow re-enables
- // interrupts (by clearing PS.INTLEVEL). This is okay even though SP
- // is unallocated because we saved state safe from interrupt dispatch.
- .global _SyscallException
-_SyscallException: // label makes tracebacks look nicer
- _entry a1, 64 // as if after a CALL4 (PS.CALLINC==1)
- // Call deep enough to force spill of entire address register file.
- _call12 .Ldeep
-1: movi a14, 0x80000000 + .Ldelta_done
- add a0, a12, a14 // clear a0 msbit (per CALL4), offset
-3: retw // return from pseudo-CALL4
-
- // NOTE: a5 still contains the exception window's exception stack frame pointer.
-.LMdon: wsr a2, PS // for XEA2, this sets EXCM; for XEA1, this sets INTLEVEL to 1; ...
- movi a2, 0 // indicate successful SYSCALL (?)
- l32i a4, a5, 32 + 8
- rsync // complete WSR to PS for safe write to EPC1
- wsr a3, EPC_1
- l32i a3, a5, 32 + 4
- l32i a5, a5, 32 + 12
- rfe_rfue
-
- .set .Ldelta_retw, (3b - 1b)
- .set .Ldelta_done, (.LMdon - 1b)
-
- .align 4
-.Ldeep: entry a1, 48
-#if XCHAL_NUM_AREGS < 64
- mov a15, a15 // touch just far enough to overflow 32
-#else
- movi a12, .Ldelta_retw // use movi/add because of relocation
- add a12, a0, a12 // set return PC as per CALL12
- _entry a1, 48 // last call was call12 so PS.CALLINC==3
- mov a12, a0 // set return PC
- _entry a1, 48
- mov a12, a0 // set return PC
- _entry a1, 16
- mov a11, a11 // touch just far enough to overflow 64
-#endif
- retw
-
-#endif /* __XTENSA_WINDOWED_ABI__ */
-
-.Lnotzero:
- movi a2, -1 /*ENOSYS*/ // system call not supported
- addi a1, a1, ESF_TOTALSIZE
- rfe_rfue
-
- .size _xtos_syscall_handler, . - _xtos_syscall_handler
-
-
-#endif /* XCHAL_HAVE_EXCEPTIONS */
-
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