sigaltstack: Add initial implementation of sigaltstack

fix ltp testcase compile error:
ltp/testcases/open_posix_testsuite/conformance/definitions/signal_h/31-1-buildonly.c:16:13: \
error: ‘sigaltstack’ undeclared (first use in this function)
   16 |  dummyvar = sigaltstack;
      |             ^~~~~~~~~~~

Signed-off-by: yangyalei <yangyalei@xiaomi.com>

include/signal.h

@@ -404,6 +404,7 @@ int  sigtimedwait(FAR const sigset_t *set, FAR struct siginfo *value,
                   FAR const struct timespec *timeout);
 int  sigsuspend(FAR const sigset_t *sigmask);
 int  sigwaitinfo(FAR const sigset_t *set, FAR struct siginfo *value);
+int  sigaltstack(FAR const stack_t *ss, FAR stack_t *oss);
 
 #undef EXTERN
 #ifdef __cplusplus

libs/libc/signal/Make.defs

@@ -22,10 +22,9 @@
 
 CSRCS += sig_addset.c sig_delset.c sig_emptyset.c sig_fillset.c
 CSRCS += sig_nandset.c sig_andset.c sig_orset.c sig_xorset.c
-CSRCS += sig_isemptyset.c
+CSRCS += sig_isemptyset.c sig_killpg.c sig_altstack.c
 CSRCS += sig_hold.c sig_ignore.c sig_ismember.c sig_pause.c sig_psignal.c
 CSRCS += sig_raise.c sig_relse.c sig_set.c sig_signal.c sig_wait.c
-CSRCS += sig_killpg.c
 
 # Add the signal directory to the build
 

libs/libc/signal/sig_altstack.c

@@ -0,0 +1,73 @@
+/****************************************************************************
+ * libs/libc/signal/sig_altstack.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 <signal.h>
+#include <errno.h>
+#include <string.h>
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: sigaltstack
+ *
+ * Description:
+ * The sigaltstack() function allows a process to define and examine the
+ * state of an alternate stack for signal handlers for the current thread.
+ * Signals that have been explicitly declared to execute on the alternate
+ * stack shall be delivered on the alternate stack.
+ *
+ ****************************************************************************/
+
+int sigaltstack(const stack_t *ss, stack_t *oss)
+{
+  if (ss)
+    {
+      if (ss->ss_flags & SS_DISABLE)
+        {
+          goto out;
+        }
+
+      if (ss->ss_size < MINSIGSTKSZ)
+        {
+          set_errno(ENOMEM);
+          return ERROR;
+        }
+
+      /* not support SS_ONSTACK now */
+
+      set_errno(EINVAL);
+      return ERROR;
+    }
+
+out:
+  if (oss)
+    {
+      memset(oss, 0, sizeof(*oss));
+      oss->ss_flags = SS_DISABLE;
+    }
+
+  return OK;
+}