有没有办法在Linux上构建没有文本重定位的libxml2？

Question

Good afternoon,

I am having difficulties with libxml2.

I tried to build the Perl module XML-LibXML which is part of our standard runtime environment. However, this time the installation on a RHEL5 box failed, because the build process complained about missing libxml2:

$> perl Makefile.PL LIB=/foo/lib/perl PREFIX=/foo INSTALLDIRS=site
enable native perl UTF8
running xml2-config...ok (2.7.6)
looking for -lxml2... no
looking for -llibxml2... no
libxml2 not found

However, the file was available. Starting the build with

perl Makefile.PL LIB=/usr/inform/target/lib/perl PREFIX=/usr/inform/target INSTALLDIRS=site

led to more evidence of the real problem:

[...]
Can't load 'blib/arch/auto/Conftest/Conftest.so' for module Conftest: /usr/inform/target/lib/libxml2.so.2: cannot restore segment prot after reloc: Permission denied at /usr/lib/perl5/5.8.8/i386-linux-thread-multi/DynaLoader.pm line 230.
 at test.pl line 2
[...]

After some investigations I found that the problem appears to be that libxml2.so is created with text relocation:

[tess91@INF-AW] lib$ eu-findtextrel libxml2.so.2.7.6
the file containing the function 'get_crc_table' is not compiled with -fpic/-fPIC
the file containing the function 'crc32' is not compiled with -fpic/-fPIC
the file containing the function 'gzerror' is not compiled with -fpic/-fPIC
[...]

Ans since we have SElinux active on the target machine, linking against libxml.2 failed!

Is there any possibility to create libxml2 properly, or do I have to ask the admin to twist SElinux to allow relocations?

I really can't believe I am the olny one having this problem on Linux with SElinux active. What am I missing?

Any help apprecitated!

Regards, Stefan

Answer 1

The simplest way is to have your administrator yum install libxml2-devel or even yum install perl-XML-LibXML . Otherwise, see if you can add -fPIC to the CFLAGS in the Makefile.PL .

I assume you are on 32-bit x86, any other architecture wouldn't work without -fPIC .

Answer 2

I just found a possible explanation:

During the build of libxml2 the compiler flag -fPIC is indeed used, so the code is created position independant, BUT :

When creating the shared library, the static libz is linked against it. Is that the source of my problem? That including a static lib in a shared executable taints the library by introducing non-relocatable code?

The fact that the symbols eu-findtextrel should already have pointed me in that direction, since crc32 , get_crc_table , etc. look like encryption centered code...