A Mysterious x86 Processor Has Implemented APX and x86S, Abandoned by Intel

The outlet Phoronix continues to track a mysterious implementation of the x86 architecture, originating from some corporate entity with no connection to either Intel or AMD. By all appearances, this is a startup, yet the company's engineering decisions look unexpectedly bold.

It was previously reported that the processor carries an implementation of the AMX matrix extensions with 16 and 32 tiles — this already surpasses the AMX capabilities of Intel's current server-grade Xeons. Now new details have emerged: the chip uses Advanced Performance Extensions (APX), the Flexible Return and Event Delivery (FRED) mechanism, and also x86S — that very project to purge the architecture of its historical ballast, which Intel launched but wound down in mid-2024.

A Radical Cleanup of the Architecture

The public mouthpiece for these disclosures is the well-known x86 specialist Christian Ludloff, who has worked at Google, AMD, and TI and runs the reference site sandpile.org. According to his message on the Linux kernel mailing list, he was asked to document the behavior of an implementation that runs exclusively in PM64 and PML5 modes, with support for FRED and APX — and that has already been in industrial-scale operation for more than a year.

The author of the message makes no secret of his position. In his words, after more than two decades of x86-64's existence, the outdated Legacy Mode and Compatibility Mode have fulfilled their purpose, and the time has come to shed this ballast. He recalls the timeline: Intel published the first FRED specification five years ago, and APX and x86S three years ago. FRED and APX are gradually making their way into silicon at Intel and AMD, but Intel abandoned x86S — prematurely, as it now turns out. “Someone else carried on,” the message concludes.

The missive ends almost like a manifesto: complexity should be pushed into software emulation of x86, and the “cargo cult” surrounding the architecture and the “duct tape” propping it up ought to be removed.

Who Is Behind It

The developer's identity remains a secret. If the project were backed by, say, Zhaoxin or Hygon, it would be a serious engineering leap. Among the possible candidates, Phoronix names the startup RosaicLabs, which, according to reports, gained access to Intel Atom processor designs. Building 16- and 32-tile AMX, APX, FRED, and x86S on top of an Atom-like core is an exceptionally ambitious task. What this mystery will amount to, only time will tell.

Source: Phoronix