Re: [PHP4BETA] Running PHP3 and PHP4

On Tue, Sep 07, 1999 at 11:22:43PM +0200, Zeev Suraski wrote: > At 23:09 07/09/1999 , Sascha Schumann wrote: > > I don't know exactly how versioning works in i.e. the C > > library, but I do know that it's completely transparent to > > users and developers. > > > > I see this as a benefit - if it's easy to realize and it > > doesn't interfere with other parts because of technical > > reasons, there is hardly any chance of doing something wrong. > > Well, if you could supply some more concrete information on this versioning > method, it may change my opinion. The so-called versioning is a method where you can assign symbols a certain version (status) in a shared library. For example, you might have a function called X in php3 and php4. Without versioning, the linker would not be able to choose the correct one (if there is a "correct" one at all). Versioning allows you now what you could do manually by prefixing symbol names with php3_ or php4_. The difference is that versioning works transparently. The dynamic linker decides at run-time which undefined reference to bind to which symbol by using the versioning information. Let's look at a practical example. We've got two libraries, called 1 and 2 which contain the symbol "dummy". We have an object file which accesses a symbol "dummy". This object file is now linked against lib 1 or 2 and stored in 1.so or 2.so, respectively. $ nm 1.so | grep dummy U dummy@@VER1 $ nm 2.so | grep dummy U dummy@@VER2 You see that there is still a reference to dummy, but the reference includes additional information. This information is used by the dynamic linker to find the correct symbol. Therefore, both shared objects could be used within the same executable. Versioning is supported on Solaris 2.x and in recent GNU binutils. > There are things that will simply not work right, though, because they're > 'not meant to be'. For example, the Sybase library isn't supposed to be > initialized twice within the same process; If you have both PHP 3.0 and > 4.0 in the same server, it may fuck up. I'm sure there are plenty of such > cases, where running two versions of the same thing within the same process > will cause problems. Yes, that's a problem. I don't think that's our problem though. > Considering the number of issues raised by using CGI binaries (almost none) > - I don't think it's that much of a necessity to support running both 3.0 > and 4.0 within the same server as modules. You can run 3.0 as a CGI and > 4.0 as a module or vice versa, and rarely will this pose any limitations. Well, to produce a versioned shared library (i.e. for APXS), we need to pass one additional linker flag and create a version script: PHPV4 { global: * }; `info ld', node "Version Script" contains more information. -- Regards, Sascha Schumann Consultant