[gdb/tui,c++17] Fix NULL string_view in tui_partial_win_by_name

When building gdb with CFLAGS=-std=gnu17 and CXXFLAGS=-std=gnu++17 and running
test-case gdb.tui/new-layout.exp, we run into:
...
UNRESOLVED: gdb.tui/new-layout.exp: left window box after shrink (ll corner)
FAIL: gdb.tui/new-layout.exp: right window box after shrink (ll corner)
...

In a minimal form, we run into an abort when issuing a winheight command:
...
$ gdb -tui -ex "winheight src - 5"
   <tui stuff>
Aborted (core dumped)
$
...
with this backtrace at the abort:
...
\#0  0x0000000000438db0 in std::char_traits<char>::length (__s=0x0)
     at /usr/include/c++/9/bits/char_traits.h:335
\#1  0x000000000043b72e in std::basic_string_view<char, \
   std::char_traits<char> >::basic_string_view (this=0x7fffffffd4f0, \
   __str=0x0) at /usr/include/c++/9/string_view:124
\#2  0x000000000094971b in tui_partial_win_by_name (name="src")
     at src/gdb/tui/tui-win.c:663
...
due to a NULL comparison which constructs a string_view object from NULL:
...
   657  /* Answer the window represented by name.  */
   658  static struct tui_win_info *
   659  tui_partial_win_by_name (gdb::string_view name)
   660  {
   661    struct tui_win_info *best = nullptr;
   662
   663    if (name != NULL)
...

In gdbsupport/gdb_string_view.h, we either use:
- gdb's copy of libstdc++-v3/include/experimental/string_view, or
- the standard implementation of string_view, when built with C++17 or later
  (which in gcc's case comes from libstdc++-v3/include/std/string_view)

In the first case, there's support for constructing a string_view from a NULL
pointer:
...
      /*constexpr*/ basic_string_view(const _CharT* __str)
      : _M_len{__str == nullptr ? 0 : traits_type::length(__str)},
        _M_str{__str}
      { }
...
but in the second case, there's not:
...
      __attribute__((__nonnull__)) constexpr
      basic_string_view(const _CharT* __str) noexcept
      : _M_len{traits_type::length(__str)},
        _M_str{__str}
      { }
...

Fix this by removing the NULL comparison altogether.

Build on x86_64-linux with CFLAGS=-std=gnu17 and CXXFLAGS=-std=gnu++17, and
tested.

gdb/ChangeLog:

2020-07-06  Tom de Vries  <tdevries@suse.de>

	PR tui/26205
	* tui/tui-win.c (tui_partial_win_by_name): Don't test for NULL name.

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 21dc3e2b2f9409090f9d9e7be321bd2de3f5d502..b802641c9d2777cce13c4d81d5dbcfa033dbdcfc 100644 (file)
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2020-07-06  Tom de Vries  <tdevries@suse.de>
+
+       PR tui/26205
+       * tui/tui-win.c (tui_partial_win_by_name): Don't test for NULL name.
+
 2020-07-05  Tom de Vries  <tdevries@suse.de>
 
        PR build/26187

diff --git a/gdb/tui/tui-win.c b/gdb/tui/tui-win.c
index 336571f158e30d1c7184dbafdd22d30c6acf10bf..f906b0dc4fea4a64cb70efef12c748ad1ef9aaee 100644 (file)
--- a/gdb/tui/tui-win.c
+++ b/gdb/tui/tui-win.c
@@ -660,21 +660,18 @@ tui_partial_win_by_name (gdb::string_view name)
 {
   struct tui_win_info *best = nullptr;
 
-  if (name != NULL)
+  for (tui_win_info *item : all_tui_windows ())
     {
-      for (tui_win_info *item : all_tui_windows ())
-       {
-         const char *cur_name = item->name ();
+      const char *cur_name = item->name ();
 
-         if (name == cur_name)
-           return item;
-         if (startswith (cur_name, name))
-           {
-             if (best != nullptr)
-               error (_("Window name \"%*s\" is ambiguous"),
-                      (int) name.size (), name.data ());
-             best = item;
-           }
+      if (name == cur_name)
+       return item;
+      if (startswith (cur_name, name))
+       {
+         if (best != nullptr)
+           error (_("Window name \"%*s\" is ambiguous"),
+                  (int) name.size (), name.data ());
+         best = item;
        }
     }