Missing memcached_exists symbol

[mvanbaak]

2 days ago upstream memcached module sources were pulled into the php7 branch. (commit b55106b)

With this commit the module cannot be loaded anymore:

PHP Warning:  PHP Startup: Unable to load dynamic library '/usr/lib64/php/7.0/modules/memcached.so' - /usr/lib64/php/7.0/modules/memcached.so: undefined symbol: memcached_exist in Unknown on line 0

[mvanbaak]

Probably fixed as soon as you guys sync https://github.com/awslabs/aws-elasticache-cluster-client-libmemcached with latest upstream.

[sodabrew]

Hmm. I thought memcached_exist was available in all libmemcached 1.0.x versions.

[mvanbaak]

I thought so as well, but if you look at the commit where the upstream changes are pulled, there's an ifdef for that function in php-memcached-compat. This is probably the change that breaks it (the removal of this whole c and h file).

All documents state that libmemcached 1.X is ok, but it seems the latest 3.0 version needs a newer libmemcached.

I'm not familiar with libmemcached and the php module, so this is purely a 'I think' solution without looking into the code of libmemcached itself ;-)

[sodabrew]

libmemcached Changelog:

0.53 Mon Sep 26 20:50:33 PDT 2011
  * Fix for FreeBSD/OpenBSD and -lm
  * Added memcached_exist()
  * Fix for memory when using config test.
  * CLI gained --quiet

I was the one who went ahead with removing the php_memcached_compat.c that provides the alternate memcached_exists, so I want to be sure I didn't blow it!

[mvanbaak]

I launched a clean amazon linux ami (the latest) to compile the module.
This is my ansible setup for it:

- name: Clone aws-elasticache-cluster-client-libmemcached library
  tags: awsmemcached
  git:
    repo: https://github.com/awslabs/aws-elasticache-cluster-client-libmemcached.git
    dest: /tmp/aws-libmemcached
    accept_hostkey: yes
    depth: 1

- name: Create build directory
  tags: awsmemcached
  file:
    dest: /tmp/aws-libmemcached/BUILD
    mode: 0755
    state: directory

- name: Configure aws-elasticache-cluster-client-libmemcached library
  tags: awsmemcached
  shell: >
    ../configure --prefix=/usr/local/lib/aws-libmemcached --with-pic
    chdir=/tmp/aws-libmemcached/BUILD

- name: Make and install aws-elasticache-cluster-client-libmemcached library
  tags: awsmemcached
  shell: >
    {{ item }}
    chdir=/tmp/aws-libmemcached/BUILD
  with_items:
    - make
    - make install

- name: Clone aws-elasticache-cluster-client-memcached-for-php
  tags: awsmemcached
  git:
    repo: https://github.com/awslabs/aws-elasticache-cluster-client-memcached-for-php.git
    dest: /tmp/aws-elasticache-cluster-client-memcached-for-php
    accept_hostkey: yes
    depth: 1
    version: php7

- name: Configure, compile and install aws-elasticache-cluster-client-memcached-for-php
  tags: awsmemcached
  shell: >
    {{ item }}
    chdir=/tmp/aws-elasticache-cluster-client-memcached-for-php
  with_items:
    - phpize
    - ./configure --with-libmemcached-dir=/usr/local/lib/aws-libmemcached --disable-memcached-sasl --enable-memcached-igbinary
    - sed -i "s#-lmemcached#/usr/local/lib/aws-libmemcached/lib/libmemcached.a -lcrypt -lpthread -lm -lstdc++#" Makefile
    - make
    - make install

- name: Enable aws-elasticache-cluster-client-memcached-for-php
  tags: php
  lineinfile:
    dest: "/etc/{{ php_conf_dir }}/zz-memcached.ini"
    line: "extension=memcached.so"
    create: yes

With the latest commit this gives the error undefined symbol: memcached_exist

When I checkout 7937c7f1907f74dc857ed8f34a0261bf0de89ae2 instead of HEAD of the php7 branch everything works

[malyeyev-AMZN]

Potentially relevant changes in upsteam libmemcached between 1.0.8 and 1.0.18:

diff --git a/libmemcached-1.0/exist.h b/libmemcached-1.0/exist.h
index 5c60105..ef60a81 100644
--- a/libmemcached-1.0/exist.h
+++ b/libmemcached-1.0/exist.h
@@ -36,6 +36,10 @@

#pragma once

+#ifdef __cplusplus
+extern "C" {
+#endif
+
LIBMEMCACHED_API
memcached_return_t memcached_exist(memcached_st *memc, const char *key, size_t key_length);

@@ -43,3 +47,6 @@ LIBMEMCACHED_API
memcached_return_t memcached_exist_by_key(memcached_st *memc,
const char *group_key, size_t group_key_length,
const char *key, size_t key_length);
+#ifdef __cplusplus
+}
+#endif

[sodabrew]

Is this a bug in libmemcached for visibility of that symbol to C linkage?

[malyeyev-AMZN]

@mvanbaak do you by any chance have multiple versions of libmemcached installed?
sudo yum list installed | grep libmem

[malyeyev-AMZN]

Still can't reproduce it.

Unlikely but this may also be related to libmemcachedutil library. Just to rule it out, could you please try (between running ./configure and make) using the following

sed -i "s#-lmemcached\b#/usr/local/lib/aws-libmemcached/lib/libmemcached.a -lcrypt -lpthread -lm -lstdc++#" Makefile && sed -i "s#-lmemcachedutil\b#/usr/local/lib/aws-libmemcached/lib/libmemcachedutil.a#" Makefile
instead of
sed -i "s#-lmemcached#/usr/local/lib/aws-libmemcached/lib/libmemcached.a -lcrypt -lpthread -lm -lstdc++#" Makefile

[mvanbaak]

I'll test that later tonight. Sorry, bit busy at the moment

[malyeyev-AMZN]

@mvanbaak
Also I can't run your playbook

ansible-playbook -i "localhost," -c local issue-12.yml
ERROR! 'git' is not a valid attribute for a Play

The error appears to have been in '/home/ec2-user/issue-12.yml': line 1, column 3, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:


- name: Clone aws-elasticache-cluster-client-libmemcached library
  ^ here

[malyeyev-AMZN]

Ok, able to reproduce now and debugging it.

[malyeyev-AMZN]

@sodabrew looks like one of the changes upstream broke it:

php-memcached-dev/php-memcached@c564fd8#diff-9441255ac664d11fa292d9fb7ce03320L24

]$ nm /tmp/aws-elasticache-cluster-client-memcached-for-php/modules/memcached.so | grep memcached_exist
                 U memcached_exist
]$ nm /usr/local/lib/aws-libmemcached/lib/libmemcached.a | grep memcached_exist
00000000000003f5 T _Z15memcached_existP12memcached_stPKcm
000000000000042a T _Z22memcached_exist_by_keyP12memcached_stPKcmS2_m