Linking 32-bit library to 64-bit program

Question

I have a 32-bit .so binary-only library and I have to generate 64-bit program that uses it. Is there a way to wrap or convert it, so it can be used with 64-bit program?

Solution 1

No. You can't directly link to 32bit code inside of a 64bit program.

The best option is to compile a 32bit (standalone) program that can run on your 64bit platform (using ia32), and then use a form of inter-process communication to communicate to it from your 64bit program.

Solution 2

For an example of using IPC to run 32-bit plugins from 64-bit code, look at the open source NSPluginWrapper.

Solution 3

It is possible, but not without some serious magic behind the scenes and you will not like the answer. Either emulate a 32 bit CPU (no I am not kidding) or switch the main process back to 32 bit. Emulating may be slow though.

This is a proof of concept of the technique.

Then keep a table of every memory access to and from the 32 bit library and keep them in sync. It is very hard to get to a theoretical completeness, but something workable should be pretty easy, but very tedious.

In most cases, I believe two processes and then IPC between the two may actually be easiest, as suggested othwerwise.

Comments

[t0mm13b]

@Reed: Then how did Win95 manage the transition from 32bit code calling 16bit a la 'thunking' ? Was that at the assembler level to change around the stack pointer and registers?

[Reed Copsey]

The OS handled this explicitly, but there is nothing that allows this in Linux or modern 64bit Windows operating systems, so you have to use a workaround like I posted.

[t0mm13b]

@Reed: Thanks for answering my question. :)

[Admin]

@Reed: what IPC mechanism would you recommend? I think that shared memory should be reasonable faster then e.g. pipes or Unix Doman Sockets.

[hookenz]

Well that's a shame. Thunking was a very useful technique and allowed you to be able to call 16bit dll's from 32bit apps, or in one case that I had I needed to call a 32bit dll from a 16bit app. It's unfortuante that the modern OS's don't provide that capability for 32/64bit code. I guess there is a reason for it... maybe complexity.

[phuclv]

x86_64 use a different calling convention than x86, as well as different number of regiters (double) makes it harder to link the 2 architectures all together