RISC-V: Add crt0 file

Contains the code for the user process signal trampoline.

arch/risc-v/src/Makefile

@@ -131,6 +131,9 @@ $(AOBJS) $(UAOBJS) $(HEAD_OBJ): %$(OBJEXT): %.S
 $(COBJS) $(UCOBJS): %$(OBJEXT): %.c
 	$(call COMPILE, $<, $@)
 
+crt0$(OBJEXT): %$(OBJEXT): %.c
+	$(call COMPILE, $<, $@)
+
 ifeq ($(CONFIG_BUILD_FLAT),y)
 $(BIN): $(OBJS)
 	$(call ARCHIVE, $@, $(OBJS))

arch/risc-v/src/common/crt0.c

@@ -0,0 +1,137 @@
+/****************************************************************************
+ * arch/risc-v/src/common/crt0.c
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <arch/syscall.h>
+
+#include <nuttx/addrenv.h>
+#include <nuttx/compiler.h>
+#include <nuttx/config.h>
+
+#include <sys/types.h>
+#include <stdlib.h>
+
+#ifdef CONFIG_BUILD_KERNEL
+
+/****************************************************************************
+ * Public Function Prototypes
+ ****************************************************************************/
+
+int main(int argc, char *argv[]);
+
+/****************************************************************************
+ * Private Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: up_signal_handler
+ *
+ * Description:
+ *   This function is the user-space, signal handler trampoline function.  It
+ *   is called from up_signal_dispatch() in user-mode.
+ *
+ * Input Parameters:
+ *   a0 = sighand
+ *     The address user-space signal handling function
+ *   a1-a3 = signo, info, and ucontext
+ *     Standard arguments to be passed to the signal handling function.
+ *
+ * Returned Value:
+ *   None.  This function does not return in the normal sense.  It returns
+ *   via the SYS_signal_handler_return (see syscall.h)
+ *
+ ****************************************************************************/
+
+static void sig_trampoline(void) naked_function;
+static void sig_trampoline(void)
+{
+  __asm__ __volatile__
+  (
+    " addi sp, sp, -16\n"   /* Save ra on the stack */
+    " sd   ra, 8(sp)\n"
+    " mv   t0, a0\n"        /* t0=sighand */
+    " mv   a0, a1\n"        /* a0=signo */
+    " mv   a1, a2\n"        /* a1=info */
+    " mv   a2, a3\n"        /* a2=ucontext */
+    " jalr t0\n"            /* Call the signal handler (modifies ra) */
+    " ld   ra, 8(sp)\n"     /* Recover ra in sp */
+    " addi sp, sp, 16\n"
+    " li   a0, %0\n"        /* SYS_signal_handler_return */
+    " ecall\n"              /* Return from the SYSCALL */
+    " nop\n"
+    :
+    : "i" (SYS_signal_handler_return)
+    :
+  );
+}
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: _start
+ *
+ * Description:
+ *   This function is the low level entry point into the main thread of
+ *   execution of a task.  It receives initial control when the task is
+ *   started and calls main entry point of the newly started task.
+ *
+ * Input Parameters:
+ *   argc - The number of parameters being passed.
+ *   argv - The parameters being passed. These lie in kernel-space memory
+ *     and will have to be reallocated  in user-space memory.
+ *
+ * Returned Value:
+ *   This function should not return.  It should call the user-mode start-up
+ *   main() function.  If that function returns, this function will call
+ *   exit.
+ *
+ ****************************************************************************/
+
+void _start(int argc, FAR char *argv[])
+{
+  int ret;
+
+  /* Initialize the reserved area at the beginning of the .bss/.data region
+   * that is visible to the RTOS.
+   */
+
+  ARCH_DATA_RESERVE->ar_sigtramp = (addrenv_sigtramp_t)sig_trampoline;
+
+  /* Call C++ constructors */
+
+  /* Setup so that C++ destructors called on task exit */
+
+  /* REVISIT: Missing logic */
+
+  /* Call the main() entry point passing argc and argv. */
+
+  ret = main(argc, argv);
+
+  /* Call exit() if/when the main() returns */
+
+  exit(ret);
+}
+
+#endif /* CONFIG_BUILD_KERNEL */

arch/risc-v/src/mpfs/Make.defs

@@ -22,6 +22,10 @@
 
 CMN_ASRCS += mpfs_head.S riscv_vectors.S riscv_exception_common.S riscv_testset.S
 
+ifeq ($(CONFIG_BUILD_KERNEL),y)
+STARTUP_OBJS = crt0$(OBJEXT)
+endif
+
 # Specify C code within the common directory to be included
 CMN_CSRCS += riscv_initialize.c riscv_swint.c
 CMN_CSRCS += riscv_createstack.c riscv_exit.c riscv_fault.c