library interposition

zeegeek · 10-25-2009, 12:45 AM

Hi,

I'm writing a simple libc interposition library for some library calls like open(), connect(), etc. However, it didn't seem to work on php's mysql module in particular. I created a simple php script which creates a connection to a mysql database, then closes it. However, none of the connect() calls showed up in my trace log produced by my interposition library. strace does show the connect() system call took place. I also used ltrace to see if the actual libc connect() was called, but it didn't show up. So it leads to the thinking of maybe the mysql module in php is statically linked. But running 'file' on the module said differently. 'ldd' also showed that it links to libc.

Is php compiled so that it's statically linked by default? If not, what else might cause it to make system calls without calling the corresponding libc functions?

I'm using Fedora 11 64-bit version.

Thank you.

Sergei Steshenko · 10-26-2009, 02:21 AM

Quote:

Originally Posted by zeegeek

Hi,

I'm writing a simple libc interposition library for some library calls like open(), connect(), etc. However, it didn't seem to work on php's mysql module in particular. I created a simple php script which creates a connection to a mysql database, then closes it. However, none of the connect() calls showed up in my trace log produced by my interposition library. strace does show the connect() system call took place. I also used ltrace to see if the actual libc connect() was called, but it didn't show up. So it leads to the thinking of maybe the mysql module in php is statically linked. But running 'file' on the module said differently. 'ldd' also showed that it links to libc.

Is php compiled so that it's statically linked by default? If not, what else might cause it to make system calls without calling the corresponding libc functions?

I'm using Fedora 11 64-bit version.

Thank you.

You told us nothing about what you did to make your library visible to the application.

I am particularly interested in your (in)actions regarding LD_LIBRARY_PATH, LD_RUN_PATH environment libraries.

zeegeek · 10-26-2009, 09:30 AM

Quote:

Originally Posted by Sergei Steshenko

You told us nothing about what you did to make your library visible to the application.

I am particularly interested in your (in)actions regarding LD_LIBRARY_PATH, LD_RUN_PATH environment libraries.

Sorry for the lack of information in the original post. I used LD_PRELOAD to load my library when starting the application.

As a side note, I used my library on mysql-query-browser and it seemed to catch all the library calls from mysql client library. This might help to narrow the problem down to PHP's mysql module or the way it links to mysql client library.