The Forgetful CPU (Linux on M4)

Original Article ↗ Hacker News Discussion ↗

Hackers are working to get Linux running on Apple’s new M4 Macs, uncovering quirks like a changed CPU instruction that now wipes registers to save power and breaks prior kernel assumptions. Commenters weigh the appeal of Apple’s efficient, tightly integrated hardware against its closed ecosystem, debating whether it’s wise to buy machines from a company seen as hostile or indifferent to open systems. There’s also interest in AI-assisted reverse engineering and forks like Gravity Linux, alongside broader arguments over whether energy should instead go into improving x86‑64 or open RISC‑V platforms.

Apple’s Openness and Linux on Apple Silicon

  • Debate over whether Apple is “hostile” to open systems vs simply indifferent and focused on its own stack.
  • Some argue Macs will never be fully bootloader-locked because Apple uses them as internal development machines; others think locking out alternative OSes is likely in the future.
  • Several note Apple provides almost no official support or docs for alternate OSes; everything (e.g., Asahi) is reverse-engineered.

Status of Asahi and Gravity Linux

  • One view: Asahi is effectively “dead” for new hardware (doesn’t boot on last ~2 years of Macs), and current support lacks basics like sleep/hibernate, making it feel like a future retrocomputing project.
  • Others point to Gravity Linux as an AI-assisted Asahi fork targeting M4 and later, with media coverage cited.

Mac Hardware vs Other Laptops

  • Many praise Apple Silicon laptops: excellent battery life, low heat/noise, strong performance per watt, and very good trackpads.
  • Some describe Intel-era MacBooks as noisy, hot, and poor value; others fear Apple could regress but users now have fewer alternatives.
  • Counterpoint: some report newer M-series Pros can get hot and loud under sustained load, especially without throttling like fanless Airs.

Servers, Apple Silicon, and Strategy

  • Repeated argument: Apple is a vertical company that wants to sell integrated products, not CPUs or open hardware.
  • Some think Apple could profit from server/AI chips; others argue:
    • They already sell all the chips they can make.
    • Previous Xserve efforts failed.
    • Server buyers expect modular, serviceable, and open-ish hardware/software, which clashes with Apple’s design and business model.
  • Rumors of future Apple server silicon are mentioned but acknowledged as unproven.

AI-Assisted Reverse Engineering

  • M4/M6 bring-up work is said to be AI-assisted.
  • Tension: some want faster, AI-driven progress to “just make Linux work,” while others emphasize the intrinsic hacker satisfaction of manual RE and resent AI being proposed as the default answer to every hard problem.

Trackpads and Protocols

  • One claim: third-party trackpads are poor on macOS because Apple’s gesture/touchpad protocols are proprietary, forcing emulated mice.
  • Others rebut:
    • macOS input events are easy to spoof; protocol isn’t the main blocker.
    • The difference is in Apple’s hardware, haptics, and tuning, not closed APIs.
  • Some insist premium Windows laptops now have comparable trackpads; others challenge this and also ask about Linux compatibility.

OS Experience: macOS, Windows, Linux

  • Several developers like macOS as a desktop OS but dislike Apple’s keyboard/trackpad layout on laptops and various UX quirks.
  • Strong criticism of “corporate Windows”: heavy management, security tools, cloud integration, and Acrobat/Defender overhead make systems slow and frustrating.
  • Some respond that many issues are corporate policy/config, not inherent to Windows. Others note corporate spyware can degrade macOS similarly.
  • A recurring stance: personal Macs are delightful; corporate machines of any OS tend to be miserable.

Free Software, Hardware Choice, and Ecosystems

  • Some argue buying tightly integrated Apple hardware harms the long-term health of free software, which historically thrived on documented, general-purpose PC ecosystems.
  • They urge developers/power users to favor more open x86-64 or RISC-V platforms, even at some performance or cost penalty.
  • Counterpoint: Microsoft also has a long history of lock-in (OEM deals, proprietary drivers, ACPI quirks, Secure Boot), so it’s not the “open” foil to Apple.
  • Others emphasize that Linux-on-Mac demand is niche; catering to it wouldn’t materially grow Apple and would create support burdens.

Technical Root Cause Discussed

  • A key detail from the article is reiterated:
    • Older Apple Silicon allowed configuring the ARM WFI (wait-for-interrupt) instruction to preserve or clear registers.
    • Linux assumed registers were preserved across WFI.
    • On M4, the configurability was removed and WFI always clears registers to save power, breaking that assumption and causing subtle bugs.