t/apr-ext failures at gcc -O0

Hi,

we're seeing t/apr-ext failures when building without optimization on
current Debian unstable (Apache 2.4.10, Perl 5.18.2). An example is

  t/apr-ext/base64.t ...................... Can't load '/home/niko/tmp/libapache2-mod-perl2/blib/arch/auto/APR/APR.so' for module APR: /home/niko/tmp/libapache2-mod-perl2/blib/arch/auto/APR/APR.so: undefined symbol: perl_module at /usr/lib/perl/5.18/DynaLoader.pm line 184.
   at /home/niko/tmp/libapache2-mod-perl2/blib/lib/APR/Base64.pm line 23.
  Compilation failed in require at /home/niko/tmp/libapache2-mod-perl2/blib/lib/APR/Base64.pm line 23.
  BEGIN failed--compilation aborted at /home/niko/tmp/libapache2-mod-perl2/blib/lib/APR/Base64.pm line 23.
  Compilation failed in require at /home/niko/tmp/libapache2-mod-perl2/t/lib/TestAPRlib/base64.pm line 12.
  BEGIN failed--compilation aborted at /home/niko/tmp/libapache2-mod-perl2/t/lib/TestAPRlib/base64.pm line 12.
  Compilation failed in require at t/apr-ext/base64.t line 8.
  BEGIN failed--compilation aborted at t/apr-ext/base64.t line 8.
  t/apr-ext/base64.t ...................... Dubious, test returned 2 (wstat 512, 0x200)
  No subtests run 
 
It looks like APR.so can only be loaded from inside mod_perl:

 % perl -Iblib/lib -Iblib/arch -MAPR -e1
 Can't load 'blib/arch/auto/APR/APR.so' for module APR: blib/arch/auto/APR/APR.so: undefined symbol: perl_module
at /usr/lib/perl/5.18/DynaLoader.pm line 184.
  at -e line 0.
 Compilation failed in require.
 BEGIN failed--compilation aborted.

The problem comes from src/modules/perl/modperl_apache_includes.h:

 #if !defined(MP_IN_XS) && AP_MODULE_MAGIC_AT_LEAST(20100606, 0)
 APLOG_USE_MODULE(perl);
 #endif

where APLOG_USE_MODULE(perl) expands via /usr/include/apache2/http_config.h to

 extern module perl_module; static int * const aplog_module_index = &(perl_module.module_index);

At -O2, this is optimized away when it's not used, but -O0 keeps it.

The MP_IN_XS guard looks promising; defining that for the APR (and
APR/PerlIO) build seems to help.  I was able to get the test suite pass
at both -O0 and -O2 with the attached patch.

It seems possible that other parts of xs/ are affected too but aren't
exercised by the test suite.

The history of MP_IN_XS usage is just

 http://svn.apache.org/viewvc?view=revision&revision=1410295
 http://svn.apache.org/viewvc?view=revision&revision=68792

but it looks like a "correct" solution to me. Does that make sense?

I'm attaching a patch that modifies the Makefile.PL files accordingly.
I expect there are other ways to accomplish the same thing too.

This is also https://bugs.debian.org/756989 (cc'd).
-- 
Niko Tyni   [email protected]


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From 91c69a8df6d63c2bea0377e59e7b58a81d60f607 Mon Sep 17 00:00:00 2001
From: Niko Tyni <[email protected]>
Date: Mon, 4 Aug 2014 10:32:36 +0300
Subject: [PATCH] Define MP_IN_XS to avoid referencing &perl_module outside of
 mod_perl

APLOG_USE_MODULE(perl) expands to

 extern module perl_module; static int * const aplog_module_index = &(perl_module.module_index);

which makes loading APR.so impossible outside mod_perl unless
aplog_module_index is optimized away by the compiler.
This causes mod_perl test suite failures in t/apr-ext at "gcc -O0".

See also
 http://svn.apache.org/viewvc?view=revision&revision=68792
 http://svn.apache.org/viewvc?view=revision&revision=1410295

Bug-Debian: https://bugs.debian.org/756989
---
 xs/APR/APR/Makefile.PL    | 7 +++++++
 xs/APR/PerlIO/Makefile.PL | 3 +++
 2 files changed, 10 insertions(+)

diff --git a/xs/APR/APR/Makefile.PL b/xs/APR/APR/Makefile.PL
index 8745a54..d569dde 100644
--- a/xs/APR/APR/Makefile.PL
+++ b/xs/APR/APR/Makefile.PL
@@ -25,6 +25,13 @@ $libs = delete $args{LIBS} if $args{LIBS};
 
 my $build = ModPerl::BuildMM::build_config();
 
+my $ccopts = $build->ccopts;
+
+# avoid referencing &perl_module outside of mod_perl
+$ccopts .= ' -DMP_IN_XS';
+
+$args{CCFLAGS} = $ccopts;
+
 my @apru_link_flags = $build->apru_link_flags;
 $libs .= join ' ', @apru_link_flags if @apru_link_flags;
 
diff --git a/xs/APR/PerlIO/Makefile.PL b/xs/APR/PerlIO/Makefile.PL
index 4a8f60d..ca102bb 100644
--- a/xs/APR/PerlIO/Makefile.PL
+++ b/xs/APR/PerlIO/Makefile.PL
@@ -25,6 +25,9 @@ if ($build->has_large_files_conflict) {
         : '';
 }
 
+# avoid referencing &perl_module outside of mod_perl
+$ccopts .= ' -DMP_IN_XS';
+
 ModPerl::BuildMM::WriteMakefile(
     NAME         => 'APR::PerlIO',
     VERSION_FROM => 'PerlIO.pm',
-- 
2.0.1