Runtime page size detection

[archbirdplus]

This PR implements runtime page sizes. Closes #4082. Closes #11308. Closes #16331. Closes #20714.

Notable changes:

• Introduce pageSize() to get the runtime page size.
• Correct the use of page_size in the standard library.
• Move page_size to from std.mem to std.heap.
• Rename page_size to min_page_size.
• Introduce max_page_size to get the comptime upper bound on page size.

Not implemented (debatable):

• Zig could have a dedicated alignPage alignment. This would generate slightly stricter runtime validation than the current align(min_page_size).
• Zig could add a compile option to override the page size. This wouldn't optimize much besides the GPA, but it would provide users with a fallback before editing the standard library.

[notcancername]

Hi, thanks so much for putting in the work to make runtime page size a reality :) These else prongs in heap.zig worry me, it seems too easy to add an architecture and have an incorrect page size set as default. I think a compile error would be more appropriate. Also, I think it would be good if pageSize was marked inline to propagate the comptime-ness of the result.

[archbirdplus]

@notcancername

Inlining:
Looks like pageSize is already comptime and inlined during optimization. Comptime is a problem though. It suggests to some people that their code is valid when it isn't. I would like to ban the use of this function in comptime-dependent cases, demanding that the user prove that pageSize will be comptime (in which case they should use page_size instead). But sniffing for comptime is a bug, not a feature: #7539 (comment).
Since inlining has no semantic difference, I'll inline it anyways.

Else:
Do you mean the page_size else prongs? I suppose it's fine to break the few projects that depended on that.

[notcancername]

I would like to ban the use of this function in comptime-dependent cases, demanding that the user prove that pageSize will be comptime (in which case they should use page_size instead).

Thanks, I am in favor of this. I believe you may be able to achieve this by assigning to a var and returning that. For what it's worth, #868 has been implemented, so you might want to use that.

Do you mean the page_size else prongs? I suppose it's fine to break the few projects that depended on that.

Yes, page_size should match all current CPU architectures, so that when a new architecture is added, the implementer gets a compile error when code tries to access page_size (ditto for page_size_cap), and adds the correct value.

[archbirdplus]

Local tests now pass. I just can't figure out how to test on Windows.

[archbirdplus]

I'd like to re-run CI. I cannot get local tests to pass, but I would like to see how the CI runner behaves.

There seems to be another issue besides page size that prevents me from running tests myself.
Running the test command from the CI script on Asahi Linux fails like so:

+ ./stage4/bin/zig build test docs --maxrss 24696061952 -fwasmtime -Denable-llvm -Dtarget=native-native-musl --zig-lib-dir /home/arch/zig/lib --cache-dir /home/arch/zig/builddir-alt/.zig-cache -Dskip-release
test
└─ zig build-exe zig Debug native-native-musl 2 errors
error: ld.lld: undefined symbol: __libc_single_threaded
    note: referenced by zig_llvm.cpp
    note:               zig_llvm.cpp.o:(ZigLLVMCreateTargetMachine) in archive /home/arch/zig/builddir-alt/zigcpp/libzigcpp.a
    note: referenced by zig_llvm.cpp
    note:               zig_llvm.cpp.o:(ZigLLVMCreateTargetMachine) in archive /home/arch/zig/builddir-alt/zigcpp/libzigcpp.a
    note: referenced by zig_clang.cpp
    note:               zig_clang.cpp.o:(ZigClangLoadFromCommandLine) in archive /home/arch/zig/builddir-alt/zigcpp/libzigcpp.a
    note: referenced 17 more times
error: ld.lld: undefined symbol: __isoc23_strtol
    note: referenced by zig_llvm.cpp
    note:               zig_llvm.cpp.o:(ZigLLVMTargetMachineEmitToFile) in archive /home/arch/zig/builddir-alt/zigcpp/libzigcpp.a
error: the following command failed with 2 compilation errors:
/home/arch/zig/builddir-alt/stage4/bin/zig build-exe --stack 33554432 /home/arch/zig/builddir-alt/zigcpp/libzigcpp.a /usr/lib64/libclang-cpp.so /usr/lib64/liblldMinGW.so /usr/lib64/liblldELF.so /usr/lib64/liblldCOFF.so /usr/lib64/liblldWasm.so /usr/lib64/liblldMachO.so /usr/lib64/liblldCommon.so /usr/lib64/libLLVM-18.so -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=600 -ltinfo /usr/lib64/libz.so /usr/lib/gcc/aarch64-redhat-linux/14/libstdc++.so -lunwind -fno-sanitize-thread -ODebug -target native-native-musl -mcpu native -I /usr/include -I /usr/include -L /usr/lib64 --dep aro --dep aro_translate_c --dep build_options -Mroot=/home/arch/zig/src/main.zig -Maro=/home/arch/zig/lib/compiler/aro/aro.zig --dep aro -Maro_translate_c=/home/arch/zig/lib/compiler/aro_translate_c.zig -Mbuild_options=/home/arch/zig/builddir-alt/.zig-cache/c/e867395cb58fc12949748f95b1b06d98/options.zig -lc --cache-dir /home/arch/zig/builddir-alt/.zig-cache --global-cache-dir /home/arch/.cache/zig --name zig --zig-lib-dir /home/arch/zig/lib/ --listen=-
test
└─ test-std
   └─ run test std-wasm32-wasi.0.1...0.1-musl-generic-Debug-libc 2600/2718 passed, 1 failed, 117 skipped
error: 'fs.test.test.file operations on directories' failed: expected error.IsDir, found fs.File{ .handle = 7 }
Unable to dump stack trace: not implemented for Wasm
error: while executing test 'zig.system.darwin.macos.test.detect', the following test command failed:
wasmtime --dir=. -- /home/arch/zig/builddir-alt/.zig-cache/o/0d427260497117aec1db32d42886460a/test.wasm --seed=0x563739fd --listen=-

Whether I use this PR or just edit the page_size alone, the errors are the same, so at least I haven't created any new errors. Before rebasing this PR today, I had completely different errors about the wasmtime test runner reaching unreachable code while parsing arguments.
Running tests without any changes to Zig would crash with the classic #16331.

Do these errors suggest anything in particular? Maybe I didn't replicate the CI script closely enough?

[alexrp]

I think you might need to rebase this on master for CI to run? 🤔

[archbirdplus]

We are now missing only runtime querying for plan9, and comptime sizes for contiki, rtems, elfiamcu, hermit, aix, zos, and GPU targets. There targets are all either too confusing or too closed source for me to add.

[alexrp]

Other than the Plan 9 comment above, I think I'm comfortable signing off on the page size values picked here and the overall direction of the changes. @andrewrk I think now would be a good time for you to review the resulting changes throughout the standard library; you're probably more qualified for that than me.

[andrewrk]

Thanks, looking now.

[pfgithub]

Is this supposed to say helper method for pageSize()? It says it's a helper method for itself right now.