Kbuild: Assembly code extension.

This commit set back .S as the assembly code extension for Kbuild.

Change-Id: Ib0119876bd0bed6617bbfbad2ca6a44e172ab042
Signed-off-by: Juan Manuel Cruz <juan.m.cruz.alcaraz@linux.intel.com>

arch/arm/core/exc_exit.S

@@ -0,0 +1,128 @@
+/* exc_exit.S - ARM CORTEX-M3 exception/interrupt exit API */
+
+/*
+ * Copyright (c) 2013-2014 Wind River Systems, Inc.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1) Redistributions of source code must retain the above copyright notice,
+ * this list of conditions and the following disclaimer.
+ *
+ * 2) Redistributions in binary form must reproduce the above copyright notice,
+ * this list of conditions and the following disclaimer in the documentation
+ * and/or other materials provided with the distribution.
+ *
+ * 3) Neither the name of Wind River Systems nor the names of its contributors
+ * may be used to endorse or promote products derived from this software without
+ * specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/*
+DESCRIPTION
+
+Provides functions for performing kernel handling when exiting exceptions or
+interrupts that are installed directly in the vector table (i.e. that are not
+wrapped around by _isr_wrapper()).
+*/
+
+#define _ASMLANGUAGE
+
+#include <nanok.h>
+#include <offsets.h>
+#include <toolchain.h>
+#include <arch/cpu.h>
+
+_ASM_FILE_PROLOGUE
+
+GTEXT(_ExcExit)
+GTEXT(_IntExit)
+GDATA(_nanokernel)
+
+#if CONFIG_GDB_INFO
+  #define _EXIT_EXC_IF_FIBER_PREEMPTED beq _ExcExitWithGdbStub
+#else
+  _EXIT_EXC_IF_FIBER_PREEMPTED:      .macro
+                                     it eq
+                                     bxeq lr
+                                     .endm
+#endif
+#define _EXIT_EXC_IF_FIBER_NOT_READY _EXIT_EXC_IF_FIBER_PREEMPTED
+
+/*******************************************************************************
+*
+* _IntExit - kernel housekeeping when exiting interrupt handler installed
+*            directly in vector table
+*
+* Kernel allows installing interrupt handlers (ISRs) directly into the vector
+* table to get the lowest interrupt latency possible. This allows the ISR to be
+* invoked directly without going through a software interrupt table. However,
+* upon exiting the ISR, some kernel work must still be performed, namely
+* possible context switching. While ISRs connected in the software interrupt
+* table do this automatically via a wrapper, ISRs connected directly in the
+* vector table must invoke _IntExit() as the *very last* action before
+* returning.
+*
+* e.g.
+*
+* void myISR(void)
+*     {
+*     printk("in %s\n", __FUNCTION__);
+*     doStuff();
+*     _IntExit();
+*     }
+*
+* RETURNS: N/A
+*/
+
+SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _IntExit)
+
+/* _IntExit falls through to _ExcExit (they are aliases of each other) */
+
+
+/*******************************************************************************
+*
+* _ExcExit - kernel housekeeping when exiting exception handler installed
+*            directly in vector table
+*
+* See _IntExit().
+*
+* RETURNS: N/A
+*/
+
+SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _ExcExit)
+
+    ldr r1, =_nanokernel
+
+    /* is the current thread preemptible (task) ? */
+    ldr r2, [r1, #__tNANO_flags_OFFSET]
+    ands.w r2, #PREEMPTIBLE
+    _EXIT_EXC_IF_FIBER_PREEMPTED
+
+    /* is there a fiber ready ? */
+    ldr r2, [r1, #__tNANO_fiber_OFFSET]
+    cmp r2, #0
+    _EXIT_EXC_IF_FIBER_NOT_READY
+
+    /* context switch required, pend the PendSV exception */
+    ldr r1, =_SCS_ICSR
+    ldr r2, =_SCS_ICSR_PENDSV
+    str r2, [r1]
+
+_ExcExitWithGdbStub:
+
+    _GDB_STUB_EXC_EXIT
+
+    bx lr