[PATCH v2 0/3] C++ debugging improvements: wild matching and ABI tags

[Pedro Alves <palves at redhat dot com>]

Here's v2 of the series originally posted here:

  [PATCH 00/40] C++ debugging improvements: breakpoints, TAB completion, more
  https://sourceware.org/ml/gdb-patches/2017-06/msg00012.html

Most of the series is in, except that bits that I was really
originally after.  :-)

What remains is:

 - teaching GDB to set breakpoints on all namespaces/classes/scopes by
   default, along with a new option "break -qualified" to override the
   behavior.
 - fix setting breakpoints on symbols with [abi:cxx11] tags.

In this version I've addressed Keith's comments, and implemented his
suggestion of making "-qualified" work with linespecs too, instead of
just with explicit locations:
  https://sourceware.org/ml/gdb-patches/2017-11/msg00618.html

In v1, tests and documentation changes were in separate patches, but
since now we're down to only two distinct improvements, I've moved
tests and docs changes to the patches that actually implements each
feature.  The documentation for the ABI tags patch (patch #3) has not
changed since the previous version, and was already reviewed and
approved.  The documentation for the wild matching feature was changed
since the last revision, so may benefit from review again.

Blurb from v1 with already-merged bits stripped follows:

A few months back I was looking at making GDB use gnulib's C++
namespace mode, because the default mode has gnulib define its
replacements using macros, like "#define open rpl_open".  In C++
that's a bad idea, given that using names like "open", "close",
etc. in classes and namespaces is the natural thing to do.  E.g.,
"struct target_ops::to_open" could be "class target::open".

After experimentation, I concluded that the best would be to wrap all
of GDB in:

 namespace gdb {
 }

and so I tried it:
 https://github.com/palves/gdb/commits/palves/cxx-gdb-namespace

however, when I actually got it working and started debugging that
GDB, I immediately got frustrated with GDB's C++ support.  I.e., the
dog food didn't taste so good.

The problem was that now you'd always need to prefix every function
name with "gdb::".  I.e., "b gdb::internal_error", etc., etc.  And it
gets annoying pretty fast.

I thought that GDB should be able to do better.  I thought that maybe
GDB could infer the namespace from local context, so you'd still be
able to do "b foo", and that would find "gdb::foo".  However, that
doesn't work well, because you want to be able to conveniently set
breakpoints before starting a program, when there's no frame yet.
And, running to main doesn't help, because main is not in any
namespace.  Also, the direction linespecs / setting breakpoints is
aiming, is in not relying in local context at all.  Instead, match the
most possible, and let users filter it down if they want.  I.e., e.g.,
"b foo" sets locations in all "foo" functions in the program in all
compilation units, no matter whether they're both extern or static
function, no matter where you're currently stopped in the program.
Likewise "b source.c:foo" looks at all source files named "source.c",
not just the current source if it happens to have that name.  You can
set set a breakpoint on a C++ symbol named "some_klass::method()",
even if the current frame's language is C, not C++.  Etc., etc.

The idea then occurred to me.  How about we make GDB ignore leading
namespaces when setting breakpoints?  I.e., just like "b foo" sets a
breakpoint on all "foo"s in the program, and you can zoom in on
specific "foo" functions by specifying a source file to scope the
symbol search, like "b source.c:foo", by default we'd make "b foo" set
a breakpoint on all functions and methods named "foo" too, like
"A::foo", "B::A::foo", "(anonymous namespace)::foo", and of course
global "foo".  And then if you scope the name, like "A::foo", GDB
would find both "A::foo", and "B::A::foo", but not the others.  Etc.,
etc.  E.g.,:

  (gdb) b function[TAB]
  A::function()
  B::A::function()
  function()
  (anonymous namespace)::function()
  (gdb) b function
  Breakpoint 1 at 0x4005ce: function. (4 locations)

  (gdb) b A::function[TAB]
  A::function()
  B::A::function()
  (gdb) b function
  Breakpoint 1 at 0x4005ce: function. (2 locations)

That sounded quite promising to me.  Turns out that that's what lldb
does too, so I started experimenting with doing the same in GDB.
Along the way, I realized that gdb's Ada support has always behaved
like that...  ada-lang.c calls it "wild matching" vs "full matching"
(see full_match and wild_match).  So it's not really a new idea for
GDB.  The problem is that Ada does that on its own little ada-lang.c
corner, out of view..  

Actually, above I'm showing TAB completion.  But there's more to that.
Once it got it working for setting breakpoints, I realized that TAB
completion would need to be adjusted too.  TAB completion goes via
different symbol search code paths...  I required adjustment because
while "b foo[RET]" would find all functions named "foo", "b foo[TAB]"
would only show symbols that start with "foo"...

Fixing that required virtually rewriting how GDB interacts with
readline for completion.  Most of that rework is already in master,
but one issue is not addressed yet, which is that you want this to
happen:

  (gdb) b func[TAB]      # expands input line to ...
  (gdb) b function(      # ... this
  (gdb) b function([TAB] # another tab now shows you the candidates
  A::B::function(int)
  A::C::function(long)

Notice how the input line above was expanded to "function(", but,
that's not actually the common leading prefix between all completion
candidates!  If we'd let readline compute what it calls the "lowest
common denominator", then this is what you'd see:

  (gdb) b func[TAB]      # expands input line to ...
  (gdb) b A::            # ... this...

which is obviously bogus.

And then on top of the above, the series fixes setting breakpoints on
symbols with [abi:cxx11] tags.

Pedro Alves (3):
  Handle custom completion match prefix / LCD
  Make "break foo" find "A::foo", A::B::foo", etc. [C++ and wild
    matching]
  Breakpoints in symbols with ABI tags (PR c++/19436)

 gdb/doc/gdb.texinfo                         |  86 +++++-
 gdb/NEWS                                    |  42 +++
 gdb/ada-lang.c                              |  22 +-
 gdb/ax-gdb.c                                |   3 +-
 gdb/breakpoint.c                            |  32 ++-
 gdb/c-lang.c                                |   2 +-
 gdb/completer.c                             |  61 +++-
 gdb/completer.h                             | 139 ++++++++-
 gdb/cp-support.c                            | 218 +++++++++++++-
 gdb/cp-support.h                            |   7 +
 gdb/dwarf2read.c                            |  48 ++++
 gdb/guile/scm-breakpoint.c                  |   6 +-
 gdb/language.c                              |  11 +-
 gdb/language.h                              |   3 +-
 gdb/linespec.c                              |  52 +++-
 gdb/linespec.h                              |  12 +-
 gdb/location.c                              |  95 +++++--
 gdb/location.h                              |  38 ++-
 gdb/mi/mi-cmd-break.c                       |   3 +-
 gdb/python/py-breakpoint.c                  |   3 +-
 gdb/python/python.c                         |   3 +-
 gdb/symtab.c                                |  11 +-
 gdb/symtab.h                                |  20 +-
 gdb/testsuite/gdb.base/langs.exp            |   2 +-
 gdb/testsuite/gdb.cp/meth-typedefs.exp      |  39 ++-
 gdb/testsuite/gdb.cp/namespace.exp          |   2 +-
 gdb/testsuite/gdb.linespec/cpcompletion.exp | 423 ++++++++++++++++++++++++++++
 gdb/testsuite/gdb.linespec/cpls-abi-tag.cc  |  93 ++++++
 gdb/testsuite/gdb.linespec/cpls-abi-tag.exp | 286 +++++++++++++++++++
 gdb/testsuite/gdb.linespec/explicit.exp     |  80 +++---
 gdb/testsuite/lib/completion-support.exp    |   2 +-
 gdb/utils.c                                 |  96 ++++++-
 gdb/utils.h                                 |  16 +-
 33 files changed, 1782 insertions(+), 174 deletions(-)
 create mode 100644 gdb/testsuite/gdb.linespec/cpls-abi-tag.cc
 create mode 100644 gdb/testsuite/gdb.linespec/cpls-abi-tag.exp

-- 
2.5.5