Add a setjmp/longjmp test between user contexts

Verify that setjmp and longjmp work correctly between user contexts.
Arrange stacks for uctx_func1 and uctx_func2 so that ____longjmp_chk
works when setjmp and longjmp are called from different user contexts.

Reviewed-by: Noah Goldstein <goldstein.w.n@gmail.com>

stdlib/Makefile

@@ -256,6 +256,7 @@ tests := \
   tst-strtol-locale \
   tst-strtoll \
   tst-swapcontext1 \
+  tst-swapcontext2 \
   tst-thread-quick_exit \
   tst-tininess \
   tst-unsetenv1 \

stdlib/tst-swapcontext2.c

@@ -0,0 +1,138 @@
+/* Check setjmp/longjmp between user contexts.
+   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 <stdio.h>
+#include <stdlib.h>
+#include <setjmp.h>
+#include <ucontext.h>
+#include <stackinfo.h>
+
+static ucontext_t uctx_main, uctx_func1, uctx_func2;
+const char *str1 = "\e[31mswapcontext(&uctx_func1, &uctx_main)\e[0m";
+const char *str2 = "\e[34mswapcontext(&uctx_func2, &uctx_main)\e[0m";
+const char *fmt1 = "\e[31m";
+const char *fmt2 = "\e[34m";
+static jmp_buf jmpbuf;
+
+#define handle_error(msg) \
+  do { perror(msg); exit(EXIT_FAILURE); } while (0)
+
+__attribute__((noinline, noclone))
+static void
+func4(ucontext_t *uocp, ucontext_t *ucp, const char *str, const char *fmt)
+{
+  printf("      %sfunc4: %s\e[0m\n", fmt, str);
+  if (swapcontext(uocp, ucp) == -1)
+    handle_error("swapcontext");
+  printf("      %sfunc4: returning\e[0m\n", fmt);
+}
+
+__attribute__((noinline, noclone))
+static void
+func3(ucontext_t *uocp, ucontext_t *ucp, const char *str, const char *fmt)
+{
+  printf("    %sfunc3: func4(uocp, ucp, str)\e[0m\n", fmt);
+  func4(uocp, ucp, str, fmt);
+  printf("    %sfunc3: returning\e[0m\n", fmt);
+}
+
+__attribute__((noinline, noclone))
+static void
+func1(void)
+{
+  while ( 1 )
+    {
+      printf("  \e[31mfunc1: func3(&uctx_func1, &uctx_main, str1)\e[0m\n");
+      if (setjmp (jmpbuf) != 0)
+	{
+	  printf("    %sfunc1: from longjmp\e[0m\n", fmt1);
+	  exit (EXIT_SUCCESS);
+	}
+      func3( &uctx_func1, &uctx_main, str1, fmt1);
+    }
+}
+
+__attribute__((noinline, noclone))
+static void
+func2(void)
+{
+  while ( 1 )
+    {
+      printf("  \e[34mfunc2: func3(&uctx_func2, &uctx_main, str2)\e[0m\n");
+      func3(&uctx_func2, &uctx_main, str2, fmt2);
+      printf("    %sfunc2: calling longjmp\e[0m\n", fmt2);
+      longjmp (jmpbuf, 1);
+    }
+}
+
+static int
+do_test (void)
+{
+  /* ____longjmp_chk has  */
+#if 0
+#ifdef _STACK_GROWS_DOWN
+#define called_from(this, saved) ((this) < (saved))
+#else
+#define called_from(this, saved) ((this) > (saved))
+#endif
+
+ /* If "env" is from a frame that called us, we're all set.  */
+  if (called_from(this_frame, saved_frame))
+    __longjmp (env, val);
+#endif
+  /* Arrange stacks for uctx_func1 and uctx_func2 so that called_from
+     is true when setjmp is called from uctx_func1 and longjmp is called
+     from uctx_func2.  */
+#ifdef _STACK_GROWS_DOWN
+# define UCTX_FUNC1_STACK	1
+# define UCTX_FUNC2_STACK	0
+#else
+# define UCTX_FUNC1_STACK	0
+# define UCTX_FUNC2_STACK	1
+#endif
+  char func_stack[2][16384];
+  int i;
+
+  if (getcontext(&uctx_func1) == -1)
+    handle_error("getcontext");
+  uctx_func1.uc_stack.ss_sp = func_stack[UCTX_FUNC1_STACK];
+  uctx_func1.uc_stack.ss_size = sizeof (func_stack[UCTX_FUNC1_STACK]);
+  uctx_func1.uc_link = &uctx_main;
+  makecontext(&uctx_func1, func1, 0);
+
+  if (getcontext(&uctx_func2) == -1)
+    handle_error("getcontext");
+  uctx_func2.uc_stack.ss_sp = func_stack[UCTX_FUNC2_STACK];
+  uctx_func2.uc_stack.ss_size = sizeof (func_stack[UCTX_FUNC2_STACK]);
+  uctx_func2.uc_link = &uctx_func1;
+  makecontext(&uctx_func2, func2, 0);
+
+  for ( i = 0; i < 2; i++ )
+    {
+      if (swapcontext(&uctx_main, &uctx_func1) == -1)
+	handle_error("swapcontext");
+      printf("        \e[35mmain: swapcontext(&uctx_main, &uctx_func2)\n\e[0m");
+      if (swapcontext(&uctx_main, &uctx_func2) == -1)
+	handle_error("swapcontext");
+      printf("        \e[35mmain: swapcontext(&uctx_main, &uctx_func1)\n\e[0m");
+    }
+
+  exit(EXIT_FAILURE);
+}
+
+#include <support/test-driver.c>