Linux: can you trust uname() to find out which version to load from a bundle?

[attilammagyar]

Linux: can you trust uname() to find out which version to load from a bundle?

[ygrabit]

we have such multiple locations check for Windows with Arm64EC and x64... where a Arm64EC host could load Arm64EC and x64 plugin binaries..
#if SMTG_CPU_ARM_64EC
if (instance == nullptr)
instance = loadAsPackage (inPath, architectureArm64XString);
if (instance == nullptr)
instance = loadAsPackage (inPath, architectureX64String);
#endif
maybe you could propose a way to do it for Linux?

[attilammagyar]

Unfortunately my knowledge about the internals of Linux are enough to tell that there's a problem here, but insufficient to confidently propose a solution that is both future-proof and backward compatible.

At the end of the day, the information returned by uname() comes from the init_uts_ns structure from the Linux kernel in init/version-timestamp.c. The UTS_MACHINE string macro here comes from a makefile variable with the same name which gets written into include/generated/compile.h when you run make (see scripts/mkcompile_h).

The problem is that this makefile variable can have a lot of different values (someone on StackOverflow dug up a few), and I have no idea which is compatible with which, if any. And to make things worse, future versions of the kernel may drop some of these values or introduce new ones.

My best bet would be an algorithm like this, but this would only solve the 64 bit vs. 32 bit case:

1. Let A be the architecture that uname() returned.
2. Try to load the plugin from the A + "-linux" directory.
3. If step 1 failed and A != "i686" then try i686-linux.
4. If we still haven't successfully loaded anything, and A != "i386" then try i386-linux.

I'm not sure if similar problems can occur between 64 bit architectures, and if yes, how to resolve them. :-(

[attilammagyar]

I made a PR from the proposed solution: steinbergmedia/vst3_public_sdk#57

I compiled the validator application for 32 bits, and sucessfully validated my plugin bundle with it on a 64 bit Linux.