MySQL UDF – wrong ELF class: ELFCLASS32

functionsMySQL

I'm having a problem creating a MySQL udf on my server (I was able to do it locally on OS X). I am compiling it like this on the server:

gcc $(mysql_config --cflags) -I /usr/include/mysql -I. -shared udf_median.cc -o udf_median.so

Here is the output of mysql_config –cflags

mysql_config --cflags
-I/usr/include/mysql -g -pipe -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m32 -fasynchronous-unwind-tables  -fPIC -g -fabi-version=2 -fno-omit-frame-pointer -fno-strict-aliasing -DMY_PTHREAD_FASTMUTEX=1

So from what I can tell, MySQL is compiled for 32bit (it was done via x86_64 RPM). I had to install a bunch of different packages to get it to compile (32 bit packages, I think).

When I try to do:

CREATE AGGREGATE FUNCTION median RETURNS REAL SONAME 'udf_median.so';

I get:

Can't open shared library 'udf_median.so' (errno: 11 /usr/lib64/mysql/plugin/udf_median.so: wrong ELF class: ELFCLASS32)

From what I can tell this is a conflict between 32 and 64 bit but I'm not sure on how to fix it. I tried to put the .so in /usr/lib/mysql/plugin/ however MySQL doesn't seem to be recognizing that directory.

Anyone have any recommendations?

Edit

So if I try to compile it without the mysql_config like this:

gcc -shared -fPIC -I /usr/include/mysql -o udf_median.so udf_median.cc

I get these errors:

In file included from udf_median.cc:36:
/usr/include/mysql/m_string.h: In function ‘const uchar* skip_trailing_space(const uchar*, size_t)’:
/usr/include/mysql/m_string.h:261: error: cast from ‘const uchar*’ to ‘intptr’ loses precision
/usr/include/mysql/m_string.h:263: error: cast from ‘const uchar*’ to ‘intptr’ loses precision
/usr/include/mysql/m_string.h:265: error: cast from ‘const uchar*’ to ‘intptr’ loses precision

Best Answer

Unfortunately, mysql_config contains quite a bit of black magic and quite a bit of blatant sketchiness. It's notoriously untrustworthy if you have more than one copy of it or the version doesn't match your server build.

Unfortunately, too, if you're using one from a distro (not official binaries) then that utility may not even be in the same package as the server... it's bundled with the client, which could easily be 32 bit and work just fine with a 64-bit server.

$ mysql_config
The program 'mysql_config' can be found in the following packages:
 * libmysqlclient-dev
 * libmariadbclient-dev
Try: sudo apt-get install <selected package>

Not confidence-inspiring.

$ mysql_config --version
5.5.40

Neat, I don't even have server on this particular system, and never have.

So, that gives you a sense of how much hocus pocus this little utility can sometimes offer up.

Fundamentally, though, there's this: wrong ELF class: ELFCLASS32 means you compiled the plugin for 32 bit, but your server is indeed 64 bit.

The missing piece from your compiler flags is -m64. If you add that and remove the -m32 (I'm not sure where that's coming from... mysql_config doesn't include either one on my test system) then you should be able to get that plugin to compile and install.

You have the plugin in the correct directory, or the system wouldn't have found the file to complain about the architecture it was compiled for.

Related Solutions

Mysql – how to resolve ELFCLASS32 error in thesql for UDF lib_thesqludf_sys.so

You didn't say, in your question what the "file not present" message was, but I'm guessing it's this:

ERROR 1126 (HY000) at line 29: Can't open shared library 'lib_mysqludf_sys.so' 
(errno: 0 /usr/local/mysql/lib/plugin/lib_mysqludf_sys.so: cannot open shared 
object file: No such file or directory)
ERROR: unable to install the UDF

That makes sense, because you're telling gcc to write the file to /usr/lib/lib_mysqludf_sys.so... that's the -o option in your command line. Give gcc the path MySQL is expecting and the rest of the installation should work.

gcc -m64 -fPIC -Wall -I/usr/include/mysql -I. -shared lib_mysqludf_sys.c \ 
-o /usr/local/mysql/lib/plugin/lib_mysqludf_sys.so \
-L/usr/lib/x86_64-linux-gnu/libstdc++.so.6

Also, whatever you're planning to do with this... don't say I didn't recommend against it. You're introducing both a potential security vulnerability and potentional performance and stability liability if these tools are deployed. This is not because there's anything wrong with the utility, but because of the amount of somewhat unorthodox functionality it opens up.

It's pretty cool, I admit. The lib_mysqludf_sys group of user-defined functions allow some interesting but easily-misappropriated capabilities, letting you spawn system commands and get either their generated output with sys_eval() or their return value with sys_exec() but really, I tend to suspect there's a reason why MySQL doesn't have these capabilities built in.

mysql> select sys_eval('df -k | grep xvda | tr -d "\n"') as cool_function_but_bad_idea;
+-----------------------------------------------------+
| cool_function_but_bad_idea                          |
+-----------------------------------------------------+
| /dev/xvda1       8256952   1216636   6620888  16% / |
+-----------------------------------------------------+
1 row in set (0.81 sec)

mysql> select sys_exec('/bin/false'), sys_exec('/bin/true');
+------------------------+-----------------------+
| sys_exec('/bin/false') | sys_exec('/bin/true') |
+------------------------+-----------------------+
|                    256 |                     0 |
+------------------------+-----------------------+
1 row in set (1.59 sec)

Update to address this error message:

gcc -Wall -m64 -I/usr/include/mysql -I. -shared lib_mysqludf_sys.c -o 
/usr/lib/lib_mysqludf_sys.so -fPIC gcc: error: lib_mysqludf_sys.c: No such 
file or directory gcc: fatal error: no input files compilation terminated

The statement in question is directing "gcc" to compile a 64-bit version from the source code, which is found in lib_mysqludf_sys.c. This is one of the files you downloaded, so, to compile it, you need to be inside the directory where you downloaded the lib_mysqludf_sys files. This error suggests that you aren't. The download package isn't limited to 32 bit, it's just that it only builds a 32 bit version unless you use the gcc -m64 -fPIC ... statement.

Sql-server – Different Results between stored procedure and UDF

DATEDIFF return the result in int. Change the @HoursWorked data type in your scalar value function to int instead of datetime.

Best Answer

Related Solutions

Mysql – how to resolve ELFCLASS32 error in thesql for UDF lib_thesqludf_sys.so

Sql-server – Different Results between stored procedure and UDF

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