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Status Under review
Workspace Linux for Power
Categories RHEL 8 (5639-RH8)
Created by Guest
Created on Jan 17, 2024

Add rr-debugger compatibility with POWER on Linux

rr-debugger ( provides the ability to record a test case that fails, and conveniently navigate forwards and backwards using a gdb interface to examine the program at various program states.

This can be used to solve trivial faults (e.g. without restarting a debugger/test case multiples times and each time stopping just a little bit easier to solve bugs hence being a time save.

Its big strength is solving multithreaded programs (e.g. MariaDB) where the problem exists however it only occasionally occurs. In this case a restart has more likelihood not the produce the problem so will waste a lot of time. On x86_64 bugs MariaDB has solved numerous bugs this way ( With POWER's weaker memory model the missing of a memory barrier and multiple threads results in a much harder problem to solve. So having a rr supporting POWER would be idea. An example of this is It was occasionally producible, always on ppc64le and nowhere else. A heroic effort by Timothy Pearson and Jens Axboe ( eventually resolved it by trial and effort on the kernel side. With rr support on ppc64le identifying a crypto miscalculation after a context switch may have been able to more confidently define the problem to kernel developers and provide a narrower scope for resolution up to 6 months earlier. Without easy tools, the amount of time that can be spent on a single platform is limited.

rr support Intel, AMD and some Aarch64 processors because of the features offered in hardware.

What this requires is, explicitly the 5.1 hardware constraints.

The memory states can be tracked, and bpf filters are used for syscalls, however non-deterministically instructions, darn obviously, and larx/stcx can fail (e.g., due to a transient hardware condition or an OS/hypervisor interrupt). Without these conditions recorded the replay-ability may not be accurate. Even a partial solution before this hardware support is there might be worth while. Example aarch64 implementation with hardware -

The functionality implemented by this will be portable to the various supported languages by gdb ( i.e. most compiled languages, and even scripting languages as a test case if causing a problem in the compiled language runtime.

The range of testimonials is impressive

Note a distro inclusion isn't a key requirement. Pulling down upstream source and compiling there is easy for all developers that would be the key userbase.

Idea priority High