Register offsets in arch may be unstable

[amscanne]

The register offsets defined in the various arch files are fixed offsets for the kernel pt_regs. However, the pt_regs type does not have any stability guarantees, and some architectures (e.g. MIPS) may even have structure definitions that depend on the kernel configuration. These offsets should be resolved in a similar way to tracepoint structure definitions, e.g. by simply marking ctx as pt_regs in the relevant probes.

See the comments here: #3871 (comment)