From: Andrew Pimlott [mailto:[EMAIL PROTECTED]
Hi Andrew > [This is an edited resend of a mail to Paul Marquess, BerkeleyDB > author, which bounced (my own fault) when I wrote it last August and > neglected to resend. Paul, this issue came up on debian-perl, so > I'm Cc'ing there. Actually, it is only the second half of the > original message, which is all that is relevant here.] > > I have some analysis on the Berkeley DB on Linux issue. I agree > that it is tricky, but I think you have mischaracterized it. The > problem is not that a version of Berkeley DB is included in the C > library. GNU libc does come with Berkeley DB, but it is in its own > shared library (libdb.so), and a trivial program linked with libc > will not use libdb at all (eg, "strace ls |& grep libdb" returns > nothing). Debian GNU/Linux has packages for alternate versions of > BerkeleyDB, and I verified that a test program can be linked against > them and run successfully with no interference from libc. (This > might not be true in all cases, however; I think some optional > features of GNU libc use libdb internally, such nss.) > > The main problem seems to be that, on most Linux distributions, > programs by default link to libdb as a shared library, instead of as > a static library. For example, the link line for perl includes -ldb > on both Linux and Solaris, but this is harmless on Solaris since > libdb is typically static and perl itself doesn't use libdb, so no > symbols from libdb.a are linked in; whereas on Linux, this is a > problem, because it causes libc's dynamic version of libdb to be > loaded whenever perl starts. This makes a mess when you later try > to load the libdb to which BerkeleyDB is linked. > > As often happens, while writing this mail I came up with a > workaround. When compiling your own Berkeley DB, compile it shared, > just like libc's libdb (this is done by "../dist/configure > --enable-dynamic"). Link BerkeleyDB.so against this shared libdb, > and when running perl, set LD_LIBRARY_PATH to point at the new > libdb. Then, perl and BerkeleyDB.so both load the same libdb. > > [UPDATE: I think this will only work if the lidbd you compile has > the soname that perl wants, which isn't true if "the libdb you > compile" comes from the Debian libdb2 package. However, I > definitely did get the above to work when I originally wrote this.] > > A less intrusive if uglier workaround allows you to keep > BerkeleyDB.so statically linked against libdb. If you convince perl > (actually, the dynamic linker when it loads perl) to load an empty > stub libdb.so, all will be well since perl doesn't actually use > Berkeley DB itself. You can create this stub with "touch foo.c; gcc > -shared -o libdb.so foo.c", and load it with > "LB_LIBRARY_PATH=/path/to/stub perl". Now, when you load > BerkeleyDB.so, which is statically linked to the new libdb.a, there > is no other version of libdb with which to conflict. > > I think a clean solution would be to inhibit perl linking with libdb > in the first place, since it doesn't need it. I suspect the current > behavior is an artifact of the original perl support for Berkeley DB > more than anything else. I haven't tried this, but I bet if this > were done, the problem would never have arisen. Do you agree? How > hard do you think it would be to change the perl build process? > > [UPDATE: The perl 5.6.0 in Debian testing doesn't linke to libdb. > Don't know whether this is a Debian change or a perl change, but it > should enable us to forget about this difficulty!] I created the patch to stop perl from including libdb. It is currently only officially available in development copies, but will be included in 5.6.1 (which is imminent). I assume this is what debian are using. For those who need to use existing versions of perl, I've included the patch for ALL stable versions of perl in my distribution. I also updated the comments about why it is difficult to get Perl + Berkeley DB + linux to work the way you want. cheers Paul _________________________________________________________ Do You Yahoo!? Get your free @yahoo.com address at http://mail.yahoo.com
