[HACKERS] LD_LIBRARY_PATH versus rpath
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From: Tom Lane on 5 May 2010 19:20 Over at http://archives.postgresql.org/pgsql-general/2010-05/msg00091.php we have a complaint about "make check" failing when the install is intended to overwrite existing libraries (in particular, replacing 8.4 with 9.0 libpq). I've done some off-list investigation and found that this appears to be a generic issue on Linux. pg_regress invokes psql, which depends on libpq.so, and if psql fails due to picking up the wrong libpq.so then you get behavior as described. Now, pg_regress tries to ensure that the temporary installation will work as desired by setting LD_LIBRARY_PATH to point at the temp installation's lib/ directory. However, the psql executable will by default get built with a DT_RPATH entry pointing at the intended final installation lib/. And DT_RPATH overrides LD_LIBRARY_PATH, in the Linux dynamic loader. man ld.so says: The shared libraries needed by the program are searched for in the fol- lowing order: o (ELF only) Using the directories specified in the DT_RPATH dynamic section attribute of the binary if present and DT_RUNPATH attribute does not exist. Use of DT_RPATH is deprecated. o Using the environment variable LD_LIBRARY_PATH. Except if the exe- cutable is a set-user-ID/set-group-ID binary, in which case it is ignored. o (ELF only) Using the directories specified in the DT_RUNPATH dynamic section attribute of the binary if present. o (etc etc) Given that deprecation note, and the fact that what we're doing entirely fails to work as desired, it seems like what we need to do is set DT_RUNPATH instead of DT_RPATH. Further reading discloses that the way to do that is to add "--enable-new-dtags" to the linker switches. So the question is, should we modify Makefile.linux along the lines of -rpath = -Wl,-rpath,'$(rpathdir)' +rpath = -Wl,-rpath,'$(rpathdir)',--enable-new-dtags I asked around at Red Hat and was told that this would be unlikely to have any negative side-effects, but I'm not sure how thoroughly those guys thought about the consequences for non-mainstream Linux machines. (In particular, I'm worried about really old distros possibly not having this switch.) My inclination is to try this in HEAD only and see if any problems emerge during the beta cycle. Comments? regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers(a)postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers |