bdash

It is a little more direct than that even. The application's entitlements are passed into the interpretation of the sandbox profile. It is the sandbox profile itself that determines which policies should be applied in the resulting compiled sandbox policy based on entitlements and other factors.

An example from /System/Library/Sandbox/Profiles/application.sb, the profile that is used for App Sandboxed applications, on my system:

  (when (entitlement "com.apple.security.files.downloads.read-only")
        (read-only-and-issue-extensions (home-subpath "/Downloads")))
  (when (entitlement "com.apple.security.files.downloads.read-write")
        (read-write-and-issue-extensions (home-subpath "/Downloads")))
  (when (or (entitlement "com.apple.security.files.downloads.read-only")
            (entitlement "com.apple.security.files.downloads.read-write"))
        (allow process-exec (home-subpath "/Downloads")))

App Sandbox is fundamentally a way for programs to use the underlying sandbox subsystem without having to write SBPL code themselves. When a program has opted into the App Sandbox, the system applies one of these sandbox policies automatically during app initialization. The policy examines the entitlements of the application to determine which additional resources should be permitted. See /System/Library/Sandbox/Profiles/application.sb if you're curious.

By far the biggest advantage of App Sandbox is that the policy ships along with the OS. If a system framework changes what resources it accesses in a software update, Apple can update the policy so the framework functionality still works. If your app uses a custom sandbox policy, you're on your own to both notice that something has changed and to update your policy.

The downside is that the App Sandbox policy is limiting and inflexible.

Intel's software optimization guides have similar annotations on many of their guidelines, and have done since long before LLMs were a thing. As a reader it's useful to know how impactful a given recommendation is and how generally applicable it is without having to read the more detailed explanations.

SSVE instructions are executed by the SME engine, which trades latency for throughput. SSVE is really intended to support use of SME, rather than as a replacement for Advanced SIMD on the CPU core itself.

The Apple Silicon CPU Optimization Guide has a lot of great information on SME and SSVE, along with more general information on optimizing for Apple's CPUs

A few quotes from Apple's guide that are particularly relevant to SSVE, from "SSVE Vector Execution Unit Optimization":

> Broadly, this unit is designed to support long vector and matrix operations performed on ZA storage _in the SME Processing Grid_.

> Recommendation: Use SSVE in a supporting role to enable high throughput SME grid computation.

> [Magnitude: High | Applicability: High] SSVE offers wide 64B vectors. While the ISA includes instructions that can operate on multi-vectors, the throughput is often only one 64B vector per cycle. Use SSVE to enable SME, which offers higher parallelism.

> Because of non-speculative execution, communication latencies, and in some cases long memory and computation latencies, SME engine instructions trail execution in the core by dozens to thousands of cycles. Any core compute instructions that consume data produced by the SME engine may have to wait an indeterminate (but long) amount of time for the data to arrive.

Strangely the WindowServer issue is a constant issue on my personal MacBook Pro, but I've never seen it on my identical work MacBook Pro. It seems like there's some other factor that is necessary to trigger the problem.

I'd sorta hope they are testing widely-used applications in the way that typical end users will experience them before releasing a new OS version.

This affects some of the most widely used applications on the platform, including "productivity" applications such as Slack that Apple uses internally. How did no-one at Apple notice this and do something about it prior to macOS 26 being released?

It mostly seems to be deprecated to encourage developers to use App Sandbox rather than doing custom sandboxing things. With custom sandboxing baking implementation details of system frameworks into the sandbox policy is almost unavoidable, and Apple would really rather you didn't do that as it limits their ability to make changes in the future.

The underlying sandbox subsystem is what App Sandbox uses. Apple can happily rely on implementation details of system frameworks in their policies because they can update them as the system frameworks change.

The sandbox subsystem is what all of Apple's system software uses for sandboxing, as well as many security-conscious third-party programs such as web browsers. It's not going anywhere anytime soon, despite being marked as deprecated.