Fix: task_struct backwards-compatibility with kernel versions < 5.14

[Christoph-Lutz]

The state field in task_struct has been renamed to __state in kernel version 5.14.

Due to this change, xcapture-bpf.c fails with the following error on kernel versions < 5.14:
/virtual/main.c:178:29: error: no member named '__state' in 'struct task_struct'; did you mean 'state'?

This fix adds a bunch of macros to make xcapture-bpf.c backwards compatible with kernel versions < 5.14.

Example:

#if LINUX_VERSION_MAJOR >= 5 && LINUX_VERSION_PATCHLEVEL >= 14
t->state = curtask->__state;
#else
t->state = curtask->state;
#endif

[tanelpoder]

Thanks! Yep I had that check in my code in an earlier version, but for some reason lost/removed it when changing things.

[tanelpoder]

Hey @Christoph-Lutz, I now remember why I had removed the simple version check, RHEL backports the new __state field to RHEL8's 4.18 kernel (with some other BPF features from 5.x). So, checking for kernel version alone is not enough, got to check if it's RHEL or vanilla:

I just added some comments to this issue - if you have time and a RHEL8 clone around (with RHEL kernel not UEK), feel free to play with this (otherwise I should be able to look into this over the holidays):

#51