Re: [PATCH v4 1/1] gdb: Add python support for demangling register unwind values

[Eli Zaretskii <eliz@gnu.org>]

> From: Craig Blackmore <craig.blackmore@embecosm.com>
> Cc: aburgess@redhat.com,
> 	eliz@gnu.org,
> 	Craig Blackmore <craig.blackmore@embecosm.com>
> Date: Wed, 20 May 2026 14:16:07 +0100
> 
> This patch addresses the scenario where a register value is saved in
> some mangled form on the target and gdb does not have sufficient
> information to demangle it.
> 
> After getting a register value from an unwinder, gdb will call out to
> extension languages to allow the value to be demangled.  This avoids
> having to write a new unwinder and allows the standard unwinders to be
> used.
> 
> This patch adds the python class
> `gdb.unwinder.UnwindRegisterValueTransformer` which is the base class
> for transformers which provide methods for transforming unwind register
> values.  Currently one such method is supported, `demangle`.  There is
> no similar support for mangling values being written back to the target
> as this was not something I needed to be able to do.  Such support can
> be added to the python API in future by supporting a `mangle` method.
> Currently writing back to a demangled register will produce an "Attempt
> to assign to an unmodifiable value" error.
> 
> Only one transformer can be registered globally at any one time.
> Attempting to register more than one transformer or to any other locus
> produces an error.  The function for registering transformers takes a
> locus to allow other loci to be supported in future.  Registered
> transformers are stored in a list so that registering multiple
> transformers may be supported in future.
> 
> `gdbpy_get_register_descriptor` is now externally visible as it is used
> to create a gdb.RegisterDescriptor object to pass to the `demangle`
> method.
> 
> This patch adds read-only attribute `gdb.Value.lval_type` which
> transformer methods can use to decide to skip modifying values that did
> not come directly from the target and may not need transforming, for
> example, values taken directly from DWARF.
> ---
>  gdb/NEWS                                      |  20 +++
>  gdb/doc/python.texi                           |  93 ++++++++++
>  gdb/extension-priv.h                          |   8 +
>  gdb/extension.c                               |  35 ++++
>  gdb/extension.h                               |   6 +
>  gdb/frame.c                                   |   9 +
>  gdb/guile/guile.c                             |   2 +
>  gdb/python/lib/gdb/__init__.py                |  21 +++
>  gdb/python/lib/gdb/unwinder.py                |  89 ++++++++-
>  gdb/python/py-registers.c                     |   2 +-
>  gdb/python/py-unwind.c                        | 169 ++++++++++++++++++
>  gdb/python/py-value.c                         |  21 +++
>  gdb/python/python-internal.h                  |   3 +
>  gdb/python/python.c                           |   4 +-
>  .../gdb.python/py-unwind-transformer-error.py |  33 ++++
>  .../gdb.python/py-unwind-transformer.c        |  80 +++++++++
>  .../gdb.python/py-unwind-transformer.exp      | 115 ++++++++++++
>  .../gdb.python/py-unwind-transformer.py       |  48 +++++
>  gdb/testsuite/gdb.python/py-value.exp         |   8 +
>  19 files changed, 763 insertions(+), 3 deletions(-)
>  create mode 100644 gdb/testsuite/gdb.python/py-unwind-transformer-error.py
>  create mode 100644 gdb/testsuite/gdb.python/py-unwind-transformer.c
>  create mode 100644 gdb/testsuite/gdb.python/py-unwind-transformer.exp
>  create mode 100644 gdb/testsuite/gdb.python/py-unwind-transformer.py

Thanks, the documentation parts are okay, with one minor comment:

> +gdb.unwinder.register_unwind_register_value_transformer(None, my_transformer, False)

This line is too long, please break it in two.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>