Kernel Patch Revved For Syscall User Redirection To Help Newer Windows Games On Wine

It looks like the syscall user redirection support could soon be mainlined to the kernel for this new Linux feature that was originally motivated by helping Windows games running on Wine.

The syscall user redirection support is needed for newer Windows games on Wine that are executing system call instructions without going through the Windows API. Due to avoiding the traditional API calls, Wine has an issue intercepting and emulating those system calls and thus this user redirection support will allow Wine to properly intercept them. In particular it appears to be the DRM / copy protection systems of modern games where this syscall user redirection support will help out the most.

Collabora's Gabriel Krisman Bertazi sent out the updated patch in its fourth iteration for this syscall user redirection. "Mechanism to quickly disable/enable syscall handling for a specific process and redirect to userspace via SIGSYS. This is useful for processes with parts that require syscall redirection and parts that don't, but who need to perform this boundary crossing really fast, without paying the cost of a system call to reconfigure syscall handling on each boundary transition."

Work appears to be concluding on the initial implementation and with no pending issues, we could potentially see it even for Linux 5.9 if it gets picked up by one of the relevant trees soon. But even with Linux 5.9 that puts it out-of-reach for Ubuntu 20.10 thus making it until the 2021 Linux distributions before most gamers will see the kernel-side support out-of-the-box unless with Valve's weight they manage to get Canonical and other distribution vendors to back-port the patch for their kernels.

Meanwhile the futex2 system call as another effort driven by Linux gaming appears to still be a work-in-progress as well.