Re: [Buildroot] [PATCH 1/2] package/berkeleydb: add option for historic dbm interface

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello Bernd,

On Mon,  7 Aug 2023 19:45:14 +0200
Bernd Kuhls <bernd@kuhls.net> wrote:

> Berkeley DB support in python depends on dbm, when missing python fails
> to detect libdb:
> https://github.com/python/cpython/blob/d2340ef25721b6a72d45d4508c672c4be38c67d3/configure.ac#L4002
> 
> quoting python configure log:
> checking for libdb... no
> 
> quoting python config.log:
> conftest.c:(.text.startup+0x8): undefined reference to `__db_ndbm_open'
> 
> This patch provides a configure option for the historic dbm interface
> to be used by the python package.
> 
> Signed-off-by: Bernd Kuhls <bernd@kuhls.net>

Thanks for those patches. However, I don't quite understand how it was
working in Python 3.10.

I agree that in Python 3.11, they moved some detection logic from
setup.py to configure.ac. But the actual code of dbm module hasn't
changed. Back in Python 3.10, it was already calling dbm_open(), which
gets expanded by a macro from db.h into __db_ndbm_open(). And indeed in
Python 3.10, the dbm module already has references to this symbol:

$ readelf -aW output/target/usr/lib/python3.10/lib-dynload/_dbm.cpython-310-arm-linux-gnueabihf.so  | grep "UND.*__db"
    10: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_delete
    15: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_store
    23: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_nextkey
    25: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_clearerr
    40: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_fetch
    41: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_open
    44: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_firstkey
    48: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_error
    51: 00000000     0 NOTYPE  GLOBAL DEFAULT  UND __db_ndbm_close

And those symbols are not provided by libdb-5.3.so:

$ readelf -aW output/target/usr/lib/libdb-5.3.so | grep __db_ndbm
$

But, the dbm Python module works as expected:

# python
Python 3.10.8 (main, Aug  7 2023, 22:52:15) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import dbm
>>> dbm.open("/tmp/plop", "c")
<dbm.dumb._Database object at 0x767ccc28>

So I'm really confused. How does it work in Python 3.10 ? Did we
already need the historic dbm interface back then ?

Any idea?

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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