[Bug python/29079] New: Python pretty printer does not work for class members

[Bug python/29079] New: Python pretty printer does not work for class members

[asmwarrior at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29079

            Bug ID: 29079
           Summary: Python pretty printer does not work for class members
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: python
          Assignee: unassigned at sourceware dot org
          Reporter: asmwarrior at gmail dot com
  Target Milestone: ---

When I define a Python pretty printer, I see it only works for a normal
variable, but not class member variable.

Here is a simple test case, it contains 3 files: main.cpp, reco.h and reco.cpp.

main.cpp
--------------------------------------
#include "reco.h"

class CTest
{
public:

    CTest(float input)
        :r(input), v(18), f(65.7)
    {
    }
    reco r;
    int  v;
    float f;
};

double DummyFunctionForwxreco(void *dummy)
{
    reco* p = (reco*)dummy;
    return p->getWeight();
}

int main() {

    reco sss(5.0);
    CTest ccc(7.8);

    return 0;
}
--------------------------------------

reco.h
--------------------------------------
#ifndef RECO_H
#define RECO_H

class reco {
    public:
        reco(float input);
        ~reco(void);

        virtual float getWeight();

    private:
        float weight;
};

#endif
--------------------------------------

reco.cpp
--------------------------------------
#include "reco.h"

reco::reco(float input) {
    weight = input;
}

reco::~reco(void) {
}

float reco::getWeight() {
    return weight;
}
--------------------------------------


To build the main.exe, you have to type the following command, not the "-g0"
option means you don't have debug information in the reco.o.
--------------------------------------
gcc -c -g0 reco.cpp
gcc -c -g main.cpp
g++ -o main.exe main.o reco.o
--------------------------------------

The python pretty printer test.py
--------------------------------------
import gdb
import sys

class recoPrinter:

   def __init__(self, val):
     self.val = val

   def to_string(self):
     return gdb.parse_and_eval('DummyFunctionForwxreco((void*)%s)' %
self.val.address )    # call the dummy function here!

def CustomPrettyPrinters(val):
   if str(val.type) == 'reco': return recoPrinter(val)
   return None

gdb.pretty_printers.append(CustomPrettyPrinters) 
--------------------------------------

Here is the debug session: you set the breakpoint by this command "b
main.cpp:27", and run the exe file by command "r", when it hit the breakpoint,
you can try to print some variables.

--------------------------------------
# gdb main.exe
GNU gdb (GDB) 11.2
Copyright (C) 2022 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-w64-mingw32".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from main.exe...
(gdb) b main.cpp:27
Breakpoint 1 at 0x1400015a3: file main.cpp, line 27.
(gdb) r
Starting program: E:\code\gdb-incomplete-type\main.exe

Breakpoint 1, main () at main.cpp:27
27          return 0;
(gdb) p sss
$1 = <incomplete type>
(gdb) p ccc
$2 = {r = <incomplete type>, v = 18, f = 65.6999969}
(gdb) source test.py
(gdb) p sss
$3 = 5
(gdb) p ccc
$4 = {r = <incomplete type>, v = 18, f = 65.6999969}
(gdb)

--------------------------------------


You see, the "p sss" works OK after "source test.py", but the "p ccc" is still
not good.

I think the pretty printer is simple, because I don't even use pretty printer
for std library.

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[Bug python/29079] Python pretty printer does not work for class members

[asmwarrior at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29079

--- Comment #1 from asmwarrior <asmwarrior at gmail dot com> ---
ssbssa wrote a patch to fix this issue:

Here is the patch:

================
diff --git a/gdb/valprint.c b/gdb/valprint.c
index 6b1531ef442..f540c681403 100644
--- a/gdb/valprint.c
+++ b/gdb/valprint.c
@@ -1028,16 +1028,6 @@ common_val_print (struct value *value, struct ui_file
*stream, int recurse,

   QUIT;

-  /* Ensure that the type is complete and not just a stub.  If the type is
-     only a stub and we can't find and substitute its complete type, then
-     print appropriate string and return.  */
-
-  if (real_type->is_stub ())
-    {
-      fprintf_styled (stream, metadata_style.style (), _("<incomplete
type>"));
-      return;
-    }
-
   if (!valprint_check_validity (stream, real_type, 0, value))
     return;

@@ -1048,6 +1038,16 @@ common_val_print (struct value *value, struct ui_file
*stream, int recurse,
        return;
     }

+  /* Ensure that the type is complete and not just a stub.  If the type is
+     only a stub and we can't find and substitute its complete type, then
+     print appropriate string and return.  */
+
+  if (real_type->is_stub ())
+    {
+      fprintf_styled (stream, metadata_style.style (), _("<incomplete
type>"));
+      return;
+    }
+
   /* Handle summary mode.  If the value is a scalar, print it;
      otherwise, print an ellipsis.  */
   if (options->summary && !val_print_scalar_type_p (type))

=======================================

For more details, you can see the discussion here:

Re: [solved] Creating a gdb Pretty-Printer for wxIPV4address —
https://forums.wxwidgets.org/viewtopic.php?p=211799#p211799

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[Bug python/29079] Python pretty printer does not work for class members

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29079

--- Comment #2 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Hannes Domani <ssbssa@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=7543c960b00ddea23f6105eff4358ec214a7f93c

commit 7543c960b00ddea23f6105eff4358ec214a7f93c
Author: Hannes Domani <ssbssa@yahoo.de>
Date:   Fri Dec 8 18:19:42 2023 +0100

    Use pretty printers for struct member stubs

    PR29079 shows that pretty printers can be used for an incomplete
    type (stub), but only when printing it directly, not if it's
    part of another struct:
    ```
    (gdb) p s
    $1 = {pp m_i = 5}
    (gdb) p s2
    $2 = {m_s = <incomplete type>, m_l = 20}
    ```

    The reason is simply that in common_val_print the check for stubs
    is before any pretty printer is tried.
    It works if the pretty printer is tried before the stub check:
    ```
    (gdb) p s
    $1 = {pp m_i = 5}
    (gdb) p s2
    $2 = {m_s = {pp m_i = 10}, m_l = 20}
    ```

    Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29079
    Approved-By: Tom Tromey <tom@tromey.com>

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[Bug python/29079] Python pretty printer does not work for class members

[ssbssa at sourceware dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=29079

Hannes Domani <ssbssa at sourceware dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |15.1
         Resolution|---                         |FIXED
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |ssbssa at sourceware dot org

--- Comment #3 from Hannes Domani <ssbssa at sourceware dot org> ---
Fixed.

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[Bug python/29079] Python pretty printer does not work for class members

[asmwarrior at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=29079

--- Comment #4 from asmwarrior <asmwarrior at gmail dot com> ---
It is really nice to see the patch is in gdb git now!

I see GDB 14.1 was just released recently, so will wait for the next release
15.1.

Thanks.

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