Flex and (linking) conflicts, or a possible reason why PHP and Recode are so crashy

So, this past week I was off teaching a course about programming and Linux at a company I worked for for a while now. Some of the insight about what people need to know and rarely do know are helping me to decide what to focus on in the future in my blog (and not limited to).

Today, though, I want to blog about not something I explained during the course, but something that was explained to me, about Bison and Flex. It’s related to the output of my linking script:

Symbol yytext@@ (64-bit UNIX System V ABI AMD x86-64 architecture) present 7 times
  /usr/bin/text2pcap
  /bin/zsh-4.3.4
  /usr/lib64/libgpsimcli.so.0.0.0
  /usr/lib64/librecode.so.0.0.0
  /usr/lib64/php5/bin/php-cgi
  /bin/zsh
  /usr/lib64/php5/bin/php

yytext, together with a few other yy symbols are generated by Flex when generating the code for a lexer (for what most of my readers are concerned, these are part of a parser). These symbols are private to a single parser, and should not be exported to other parsers. I wasn’t sure about their privateness so I haven’t reported them up to now, but now I am sure: they should not be shared between two different parsers.

Both librecode and PHP export their parser’s symbols, which would create a situation where the two parsers are sharing buffers and… well, let’s just say you don’t want to share a plate between someone eating Nutella, and someone else eating Pasta, would you?

This might actually cause quite a few problems, and as hoffie said, recode is used by PHP and is often broken when used together other extensions. I can’t be sure the problems are all limited to this, but this is certainly a good point to start if we want to fix those.

Easy way out, would be to make sure that php executables don’t export symbols that extensions don’t need to use; proper way out would be adding to that also proper visibility inside recode itself, but I wonder if it’s still maintained, release 3.6 is quite old, and even patching it is a hard task as it doesn’t even recognise AMD64 by default.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s