Re: [PATCH 10/10] gdb/python: Add new gdb.unwinder.FrameId class

[Andrew Burgess <aburgess@redhat.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> Cc: Andrew Burgess <aburgess@redhat.com>
>> Date: Fri, 10 Mar 2023 14:55:27 +0000
>> From: Andrew Burgess via Gdb-patches <gdb-patches@sourceware.org>
>> 
>> When writing an unwinder it is necessary to create a new class to act
>> as a frame-id.  This new class is almost certainly just going to set a
>> 'sp' and 'pc' attribute within the instance.
>> 
>> This commit adds a little helper class gdb.unwinder.FrameId that does
>> this job.  Users can make use of this to avoid having to write out
>> standard boilerplate code any time they write an unwinder.
>> 
>> Of course, if the user wants their FrameId class to be more
>> complicated in some way, then they can still write their own class,
>> just like they could before.
>> 
>> I've simplified the example code in the documentation to now use the
>> new helper class, and I've also made use of this helper within the
>> testsuite.
>> 
>> Any existing user code will continue to work just as it did before
>> after this change.
>> ---
>>  gdb/NEWS                              |  5 +++
>>  gdb/doc/python.texi                   | 49 ++++++++++++++++++++++-----
>>  gdb/python/lib/gdb/unwinder.py        | 26 ++++++++++++++
>>  gdb/testsuite/gdb.python/py-unwind.py | 16 +--------
>>  4 files changed, 73 insertions(+), 23 deletions(-)
>
> Thanks.
>
>> diff --git a/gdb/NEWS b/gdb/NEWS
>> index c4f7de11c6e..c5aa256c1bd 100644
>> --- a/gdb/NEWS
>> +++ b/gdb/NEWS
>> @@ -134,6 +134,11 @@ show always-read-ctf
>>       now use either an integer or a gdb.Value object for each of its
>>       'sp', 'pc', and 'special' attributes.
>>  
>> +  ** A new class gdb.unwinder.FrameId has been added.  Instrances of
>                                                           ^^^^^^^^^^
> A typo.

Fixed.

>
>> +A helper class is provided in the @code{gdb.unwinder} module that can
>> +be used to represent a frame-id
>> +(@pxref{gdb.unwinder.FrameId,,@code{gdb.unwinder.FrameId}}).
>     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> Is this justified? does using the 3rd arg of @pxref produce a much
> better cross-reference, in both Info and printed formats?

Removed use of the third arg.

>
>> +The @var{special} argument is optional, if specified it should be a
>                                          ^             ^
> Semi-colon there, and a comma missing after "if specified".

Fixed.


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

I added you tag, but the updated patch is below in case you wanted
another look.

Thanks,
Andrew

---

commit ecab23fd2e2e7644835cdf526ad49ebc574167ed
Author: Andrew Burgess <aburgess@redhat.com>
Date:   Fri Mar 10 12:29:58 2023 +0000

    gdb/python: Add new gdb.unwinder.FrameId class
    
    When writing an unwinder it is necessary to create a new class to act
    as a frame-id.  This new class is almost certainly just going to set a
    'sp' and 'pc' attribute within the instance.
    
    This commit adds a little helper class gdb.unwinder.FrameId that does
    this job.  Users can make use of this to avoid having to write out
    standard boilerplate code any time they write an unwinder.
    
    Of course, if the user wants their FrameId class to be more
    complicated in some way, then they can still write their own class,
    just like they could before.
    
    I've simplified the example code in the documentation to now use the
    new helper class, and I've also made use of this helper within the
    testsuite.
    
    Any existing user code will continue to work just as it did before
    after this change.
    
    Reviewed-By: Eli Zaretskii <eliz@gnu.org>

diff --git a/gdb/NEWS b/gdb/NEWS
index 3b2b0e0675c..b64b050e1ed 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -142,6 +142,11 @@ show always-read-ctf
      now use either an integer or a gdb.Value object for each of its
      'sp', 'pc', and 'special' attributes.
 
+  ** A new class gdb.unwinder.FrameId has been added.  Instances of
+     this class are constructed with 'sp' (stack-pointer) and 'pc'
+     (program-counter) values, and can be used as the frame-id when
+     calling gdb.PendingFrame.create_unwind_info.
+
 *** Changes in GDB 13
 
 * MI version 1 is deprecated, and will be removed in GDB 14.
diff --git a/gdb/doc/python.texi b/gdb/doc/python.texi
index c11aa746184..48c6a148567 100644
--- a/gdb/doc/python.texi
+++ b/gdb/doc/python.texi
@@ -2782,6 +2782,7 @@
 It also provides a factory method to create a @code{gdb.UnwindInfo}
 instance to be returned to @value{GDBN}:
 
+@anchor{gdb.PendingFrame.create_unwind_info}
 @defun PendingFrame.create_unwind_info (frame_id)
 Returns a new @code{gdb.UnwindInfo} instance identified by given
 @var{frame_id}.  The @var{frame_id} is used internally by @value{GDBN}
@@ -2818,6 +2819,10 @@
 Each attribute value should either be an instance of @code{gdb.Value}
 or an integer.
 
+A helper class is provided in the @code{gdb.unwinder} module that can
+be used to represent a frame-id
+(@pxref{gdb.unwinder.FrameId}).
+
 @end defun
 
 @defun PendingFrame.architecture ()
@@ -2886,7 +2891,7 @@
 @subheading The @code{gdb.unwinder} Module
 
 @value{GDBN} comes with a @code{gdb.unwinder} module which contains
-the following class:
+the following classes:
 
 @deftp {class} gdb.unwinder.Unwinder
 The @code{Unwinder} class is a base class from which user created
@@ -2910,6 +2915,40 @@
 @end defvar
 @end deftp
 
+@anchor{gdb.unwinder.FrameId}
+@deftp {class} gdb.unwinder.FrameId
+This is a class suitable for being used as the frame-id when calling
+@code{gdb.PendingFrame.create_unwind_info}.  It is not required to use
+this class, any class with the required attribute
+(@pxref{gdb.PendingFrame.create_unwind_info}) will be accepted, but in
+most cases this class will be sufficient.
+
+@code{gdb.unwinder.FrameId} has the following method:
+
+@defun gdb.unwinder.FrameId.__init__(@var{sp}, @var{pc}, @var{special} = @code{None})
+The @var{sp} and @var{pc} arguments are required and should be either
+a @code{gdb.Value} object, or an integer.
+
+The @var{special} argument is optional; if specified, it should be a
+@code{gdb.Value} object, or an integer.
+@end defun
+
+@code{gdb.unwinder.FrameId} has the following read-only attributes:
+
+@defvar gdb.unwinder.sp
+The @var{sp} value passed to the constructor.
+@end defvar
+
+@defvar gdb.unwinder.pc
+The @var{pc} value passed to the constructor.
+@end defvar
+
+@defvar gdb.unwinder.special
+The @var{special} value passed to the constructor, or @code{None} if
+no such value was passed.
+@end defvar
+@end deftp
+
 @subheading Registering an Unwinder
 
 Object files and program spaces can have unwinders registered with
@@ -2941,13 +2980,7 @@
 Here is an example of how to structure a user created unwinder:
 
 @smallexample
-from gdb.unwinder import Unwinder
-
-class FrameId(object):
-    def __init__(self, sp, pc):
-        self.sp = sp
-        self.pc = pc
-
+from gdb.unwinder import Unwinder, FrameId
 
 class MyUnwinder(Unwinder):
     def __init__(self):
diff --git a/gdb/python/lib/gdb/unwinder.py b/gdb/python/lib/gdb/unwinder.py
index 1303245c054..140b84d3374 100644
--- a/gdb/python/lib/gdb/unwinder.py
+++ b/gdb/python/lib/gdb/unwinder.py
@@ -69,6 +69,32 @@ class Unwinder(object):
         raise NotImplementedError("Unwinder __call__.")
 
 
+class FrameId(object):
+    """A Frame-ID class for use when creating gdb.UnwindInfo objects.
+
+    Attributes (all read-only):
+        pc: Program counter value.
+        sp: The stack-pointer value.
+        special: An alternative stack-pointer value, can be None."""
+
+    def __init__(self, sp, pc, special=None):
+        self._sp = sp
+        self._pc = pc
+        self._special = special
+
+    @property
+    def sp(self):
+        return self._sp
+
+    @property
+    def pc(self):
+        return self._pc
+
+    @property
+    def special(self):
+        return self._special
+
+
 def register_unwinder(locus, unwinder, replace=False):
     """Register unwinder in given locus.
 
diff --git a/gdb/testsuite/gdb.python/py-unwind.py b/gdb/testsuite/gdb.python/py-unwind.py
index dbabb006e4b..4e110c51e3b 100644
--- a/gdb/testsuite/gdb.python/py-unwind.py
+++ b/gdb/testsuite/gdb.python/py-unwind.py
@@ -14,7 +14,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 import gdb
-from gdb.unwinder import Unwinder
+from gdb.unwinder import Unwinder, FrameId
 
 
 # These are set to test whether invalid register names cause an error.
@@ -22,20 +22,6 @@ add_saved_register_error = False
 read_register_error = False
 
 
-class FrameId(object):
-    def __init__(self, sp, pc):
-        self._sp = sp
-        self._pc = pc
-
-    @property
-    def sp(self):
-        return self._sp
-
-    @property
-    def pc(self):
-        return self._pc
-
-
 class TestUnwinder(Unwinder):
     AMD64_RBP = 6
     AMD64_RSP = 7