Add a test for setjmp/longjmp within user context

Verify that setjmp/longjmp works correctly within a user context.
Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>

stdlib/Makefile

@@ -235,6 +235,7 @@ tests := \
   tst-setcontext8 \
   tst-setcontext9 \
   tst-setcontext10 \
+  tst-setcontext11 \
   tst-strfmon_l \
   tst-strfrom \
   tst-strfrom-locale \

stdlib/tst-setcontext11.c

@@ -0,0 +1,178 @@
+/* Check setjmp/longjmp within user context.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <setjmp.h>
+#include <ucontext.h>
+#include <unistd.h>
+
+static ucontext_t ctx[3];
+static jmp_buf jmpbuf;
+
+static int was_in_f1;
+static int was_in_f2;
+static int longjmp_called;
+
+static char st2[32768];
+
+static void
+f1 (int a0, int a1, int a2, int a3)
+{
+  printf ("start f1(a0=%x,a1=%x,a2=%x,a3=%x)\n", a0, a1, a2, a3);
+
+  if (a0 != 1 || a1 != 2 || a2 != 3 || a3 != -4)
+    {
+      puts ("arg mismatch");
+      exit (EXIT_FAILURE);
+    }
+
+  if (swapcontext (&ctx[1], &ctx[2]) != 0)
+    {
+      printf ("%s: swapcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+  puts ("finish f1");
+  was_in_f1 = 1;
+}
+
+static void
+__attribute__ ((noinline, noclone))
+call_longjmp (void)
+{
+  longjmp_called = 1;
+  longjmp (jmpbuf, 1);
+}
+
+static void
+f2 (void)
+{
+  if (!longjmp_called)
+    {
+      if (setjmp (jmpbuf) == 0)
+	call_longjmp ();
+    }
+
+  puts ("start f2");
+  if (swapcontext (&ctx[2], &ctx[1]) != 0)
+    {
+      printf ("%s: swapcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+  puts ("finish f2");
+  was_in_f2 = 1;
+}
+
+volatile int global;
+static int back_in_main;
+
+static void
+check_called (void)
+{
+  if (back_in_main == 0)
+    {
+      puts ("program did not reach main again");
+      _exit (EXIT_FAILURE);
+    }
+}
+
+static int
+do_test (void)
+{
+  atexit (check_called);
+
+  char st1[32768];
+
+  puts ("making contexts");
+  if (getcontext (&ctx[1]) != 0)
+    {
+      if (errno == ENOSYS)
+	{
+	  back_in_main = 1;
+	  exit (EXIT_SUCCESS);
+	}
+
+      printf ("%s: getcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+
+  /* Play some tricks with this context.  */
+  if (++global == 1)
+    if (setcontext (&ctx[1]) != 0)
+      {
+	printf ("%s: setcontext: %m\n", __FUNCTION__);
+	exit (EXIT_FAILURE);
+      }
+  if (global != 2)
+    {
+      printf ("%s: 'global' not incremented twice\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+
+  ctx[1].uc_stack.ss_sp = st1;
+  ctx[1].uc_stack.ss_size = sizeof st1;
+  ctx[1].uc_link = &ctx[0];
+  {
+    ucontext_t tempctx = ctx[1];
+    makecontext (&ctx[1], (void (*) (void)) f1, 4, 1, 2, 3, -4);
+
+    /* Without this check, a stub makecontext can make us spin forever.  */
+    if (memcmp (&tempctx, &ctx[1], sizeof ctx[1]) == 0)
+      {
+	puts ("makecontext was a no-op, presuming not implemented");
+	return 0;
+      }
+  }
+
+  if (getcontext (&ctx[2]) != 0)
+    {
+      printf ("%s: second getcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+  ctx[2].uc_stack.ss_sp = st2;
+  ctx[2].uc_stack.ss_size = sizeof st2;
+  ctx[2].uc_link = &ctx[1];
+  makecontext (&ctx[2], f2, 0);
+
+  puts ("swapping contexts");
+  if (swapcontext (&ctx[0], &ctx[2]) != 0)
+    {
+      printf ("%s: swapcontext: %m\n", __FUNCTION__);
+      exit (EXIT_FAILURE);
+    }
+  puts ("back at main program");
+  back_in_main = 1;
+
+  if (was_in_f1 == 0)
+    {
+      puts ("didn't reach f1");
+      exit (EXIT_FAILURE);
+    }
+  if (was_in_f2 == 0)
+    {
+      puts ("didn't reach f2");
+      exit (EXIT_FAILURE);
+    }
+
+  puts ("test succeeded");
+  return 0;
+}
+
+#include <support/test-driver.c>