[Bug tui/26205] New: [tui] gdb aborts during winheight command

[Bug tui/26205] New: [tui] gdb aborts during winheight command

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

            Bug ID: 26205
           Summary: [tui] gdb aborts during winheight command
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tui
          Assignee: unassigned at sourceware dot org
          Reporter: vries at gcc dot gnu.org
  Target Milestone: ---

With test-case gdb.tui/new-layout.exp, I run into:
...
PASS: gdb.tui/new-layout.exp: horizontal display
ERROR: : spawn id exp48 not open
    while executing
"expect {
-i exp48 -timeout 10
                -re "^\[\x07\x08\x0a\x0d\]" {
                    scan $expect_out(0,string) %c val
                    set hexval [format "%02x" $val]
                    ver..."
    ("uplevel" body line 1)
    invoked from within
"uplevel $body" NONE : spawn id exp48 not open
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)
...

This minimal example already aborts (though I'm not sure this is a correct
minimal representation of the problem described above):
...
$ gdb -tui -ex "winheight src - 5"
   ...
Aborted (core dumped)                                                          
 L??   PC: ?? 
$
...

Backtrace:
...
#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 /home/vries/gdb_versions/devel/src/gdb/tui/tui-win.c:663
#3  0x000000000094a241 in tui_set_win_height_command (arg=0x7fffffffe1d8 "src -
5", 
    from_tty=1) at /home/vries/gdb_versions/devel/src/gdb/tui/tui-win.c:870
#4  0x00000000004f9abc in do_const_cfunc (c=0x122f470, args=0x7fffffffe1d8 "src
- 5", 
    from_tty=1) at /home/vries/gdb_versions/devel/src/gdb/cli/cli-decode.c:95
#5  0x00000000004fd171 in cmd_func (cmd=0x122f470, args=0x7fffffffe1d8 "src -
5", from_tty=1)
    at /home/vries/gdb_versions/devel/src/gdb/cli/cli-decode.c:2181
#6  0x000000000090daf8 in execute_command (p=0x7fffffffe1de "5", from_tty=1)
    at /home/vries/gdb_versions/devel/src/gdb/top.c:668
#7  0x000000000073c1c1 in catch_command_errors (
    command=0x90d57f <execute_command(char const*, int)>, 
    arg=0x7fffffffe1ce "winheight src - 5", from_tty=1)
    at /home/vries/gdb_versions/devel/src/gdb/main.c:457
#8  0x000000000073d598 in captured_main_1 (context=0x7fffffffdb60)
    at /home/vries/gdb_versions/devel/src/gdb/main.c:1218
#9  0x000000000073d78d in captured_main (data=0x7fffffffdb60)
    at /home/vries/gdb_versions/devel/src/gdb/main.c:1243
#10 0x000000000073d7f8 in gdb_main (args=0x7fffffffdb60)
    at /home/vries/gdb_versions/devel/src/gdb/main.c:1268
#11 0x0000000000413d39 in main (argc=9, argv=0x7fffffffdc68)
    at /home/vries/gdb_versions/devel/src/gdb/gdb.c:32
...

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[Bug tui/26205] [tui] gdb aborts during winheight command

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tromey at sourceware dot org

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[Bug tui/26205] [tui] gdb aborts during winheight command

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

--- Comment #1 from Tom de Vries <vries at gcc dot gnu.org> ---
Hmm, this is during testing the tentative patch for PR26187, doesn't reproduce
with master.  Perhaps this is normally hidden?

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[Bug tui/26205] [tui] gdb aborts during winheight command

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

--- Comment #2 from Tom Tromey <tromey at sourceware dot org> ---
C++17 string_view doesn't allow NULL, and I am going to guess
that this:

static struct tui_win_info *
tui_partial_win_by_name (gdb::string_view name)
{
  struct tui_win_info *best = nullptr;

  if (name != NULL)


... perhaps constructs a string_view from NULL to do the
comparison?  I looked at the callers and I don't see how
they could pass in NULL here...

Anyway, if so, the fix is to remove this "if".

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[Bug tui/26205] [tui] gdb aborts during winheight command

[tromey at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

--- Comment #3 from Tom Tromey <tromey at sourceware dot org> ---
FWIW I think there's still a real danger that other spots
pass NULL to string_view.  Maybe as a temporary measure we
should simply always use gdb::string_view.  Or maybe adding
some asserts and then running the test suite would flush
them all out.

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[Bug tui/26205] [tui] gdb aborts during winheight command

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

--- Comment #4 from Tom de Vries <vries at gcc dot gnu.org> ---
Hmm, chronicle of a bug foretold:
...
commit 5ac588997c3c2d032d5d5145d9245eb37354c23b
Author: Tom Tromey <tromey@adacore.com>
Date:   Tue Jun 30 07:53:03 2020 -0600

    ...   

    (Note that the build still is not clean; and also I noticed that the
    libstdc++ string_view forbids the use of nullptr ... I wonder if gdb
    violates that.)
...

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[Bug tui/26205] [tui] gdb aborts during winheight command

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

--- Comment #5 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom Tromey from comment #2)
> C++17 string_view doesn't allow NULL, and I am going to guess
> that this:
> 
> static struct tui_win_info *
> tui_partial_win_by_name (gdb::string_view name)
> {
>   struct tui_win_info *best = nullptr;
> 
>   if (name != NULL)
> 
> 
> ... perhaps constructs a string_view from NULL to do the
> comparison?  I looked at the callers and I don't see how
> they could pass in NULL here...
> 
> Anyway, if so, the fix is to remove this "if".

Patch to that effect submitted:
https://sourceware.org/pipermail/gdb-patches/2020-July/170156.html

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[Bug tui/26205] [tui] gdb aborts during winheight command

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

--- Comment #6 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #1)
> Hmm, this is during testing the tentative patch for PR26187, doesn't
> reproduce with master.  Perhaps this is normally hidden?

So, FTR, this was wrong, it does reproduce with master, but only with
CXXFLAGS=-std=gnu++17.

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[Bug tui/26205] [tui] gdb aborts during winheight command

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

--- Comment #7 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Tom de Vries <vries@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=947f7597788b646683cb37b2833ed1844ce7d1bc

commit 947f7597788b646683cb37b2833ed1844ce7d1bc
Author: Tom de Vries <tdevries@suse.de>
Date:   Mon Jul 6 09:54:43 2020 +0200

    [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.

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[Bug tui/26205] [tui] gdb aborts during winheight command

[vries at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=26205

Tom de Vries <vries at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |FIXED
   Target Milestone|---                         |10.1
             Status|NEW                         |RESOLVED

--- Comment #8 from Tom de Vries <vries at gcc dot gnu.org> ---
Patch committed, marking resolved-fixed.

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