Avoid undefined behavior in Guile exception handling

The Guile code will longjmp (via scm_throw) when an object requiring
destruction is on the stack.  This is undefined behavior.

This changes this code to run any destructors in inner scopes, and to
pass a POD to gdbscm_throw_gdb_exception.

gdb/ChangeLog
2019-04-25  Tom Tromey  <tromey@adacore.com>

	* guile/scm-exception.c (gdbscm_scm_from_gdb_exception)
	(gdbscm_throw_gdb_exception): Take a gdbscm_gdb_exception.
	* guile/scm-block.c, guile/scm-breakpoint.c, guile/scm-cmd.c,
	guile/scm-disasm.c, guile/scm-frame.c, guile/scm-lazy-string.c,
	guile/scm-math.c, guile/scm-param.c, guile/scm-ports.c,
	guile/scm-symbol.c, guile/scm-symtab.c, guile/scm-type.c,
	guile/scm-value.c: Use unpack.
	* guile/guile-internal.h (gdbscm_scm_from_gdb_exception): Take a
	gdbscm_gdb_exception.
	(gdbscm_throw_gdb_exception): Likewise.
	(struct gdbscm_gdb_exception): New.
	(unpack): New function.
	(gdbscm_wrap): Use unpack.

1 files changed, 35 insertions, 3 deletions

diff --git a/gdb/guile/guile-internal.h b/gdb/guile/guile-internal.h
index a3e02ab..8ea8706 100644
--- a/gdb/guile/guile-internal.h
+++ b/gdb/guile/guile-internal.h
@@ -353,9 +353,11 @@ extern void gdbscm_misc_error (const char *subr, int arg_pos,
 
 extern void gdbscm_throw (SCM exception) ATTRIBUTE_NORETURN;
 
-extern SCM gdbscm_scm_from_gdb_exception (struct gdb_exception exception);
+struct gdbscm_gdb_exception;
+extern SCM gdbscm_scm_from_gdb_exception
+  (const gdbscm_gdb_exception &exception);
 
-extern void gdbscm_throw_gdb_exception (struct gdb_exception exception)
+extern void gdbscm_throw_gdb_exception (gdbscm_gdb_exception exception)
   ATTRIBUTE_NORETURN;
 
 extern void gdbscm_print_exception_with_stack (SCM port, SCM stack,
@@ -650,6 +652,33 @@ extern void gdbscm_initialize_values (void);
    with a TRY/CATCH, because the dtors won't otherwise be run when a
    Guile exceptions is thrown.  */
 
+/* This is a destructor-less clone of gdb_exception.  */
+
+struct gdbscm_gdb_exception
+{
+  enum return_reason reason;
+  enum errors error;
+  /* The message is xmalloc'd.  */
+  char *message;
+};
+
+/* Return a gdbscm_gdb_exception representing EXC.  */
+
+inline gdbscm_gdb_exception
+unpack (const gdb_exception &exc)
+{
+  gdbscm_gdb_exception result;
+  result.reason = exc.reason;
+  result.error = exc.error;
+  if (exc.message == nullptr)
+    result.message = nullptr;
+  else
+    result.message = xstrdup (exc.message->c_str ());
+  /* The message should be NULL iff the reason is zero.  */
+  gdb_assert ((result.reason == 0) == (result.message == nullptr));
+  return result;
+}
+
 /* Use this after a TRY/CATCH to throw the appropriate Scheme
    exception if a GDB error occurred.  */
 
@@ -676,6 +705,7 @@ SCM
 gdbscm_wrap (Function &&func, Args &&... args)
 {
   SCM result = SCM_BOOL_F;
+  gdbscm_gdb_exception exc {};
 
   try
     {
@@ -683,9 +713,11 @@ gdbscm_wrap (Function &&func, Args &&... args)
     }
   catch (const gdb_exception &except)
     {
-      GDBSCM_HANDLE_GDB_EXCEPTION (except);
+      exc = unpack (except);
     }
 
+  GDBSCM_HANDLE_GDB_EXCEPTION (exc);
+
   if (gdbscm_is_exception (result))
     gdbscm_throw (result);