std: implement basic io and improve alloc in uefi #22226

RossComputerGuy · 2024-12-13T09:04:45Z

Largely based on #19486, this PR marks me starting to work on UEFI support in Zig again. This time, there will be multiple PR's instead of one so it becomes easier to manage. This PR simply makes the zig init example build.

I tested this in QEMU by loading in OVMF, entering the UEFI shell, loading FS0:\bin\$.efi. The zig-out can be shared by adding: -drive file=fat:rw:zig-out.

alexrp · 2024-12-13T15:39:49Z

lib/std/os/uefi.zig

@@ -1,5 +1,7 @@
 const std = @import("../std.zig");

+pub const posix = @import("uefi/posix.zig");


Last I talked with Andrew about the future of std.posix, one thing we agreed on is that probably all Windows code in std.posix should be deleted. I would expect that the exact same thing is true of UEFI, as it is also not a POSIX platform in any meaningful sense?

Yeah, I agree. The UEFI POSIX stuff is just a POSIX wrapper around the UEFI protocols. We can always ditch it. UEFI is close to Windows so I think whatever we do for Windows and POSIX, it would apply to UEFI.

alexrp · 2024-12-13T15:43:05Z

lib/std/Thread/Futex.zig

@@ -66,7 +66,7 @@ pub fn wake(ptr: *const atomic.Value(u32), max_waiters: u32) void {
    Impl.wake(ptr, max_waiters);
 }

-const Impl = if (builtin.single_threaded)
+const Impl = if (builtin.single_threaded or builtin.os.tag == .uefi)


Should UEFI be treated as a proper single-threaded target?

zig/src/target.zig

Lines 66 to 81 in 82f35c5

pub fn alwaysSingleThreaded(target: std.Target) bool {

_ = target;

return false;

}

pub fn defaultSingleThreaded(target: std.Target) bool {

switch (target.cpu.arch) {

.wasm32, .wasm64 => return true,

else => {},

}

switch (target.os.tag) {

.haiku => return true,

else => {},

}

return false;

}

Yes, I just didn't know where the source was which defined that heh.

I've updated this and changed the defaultSingleThreaded for UEFI.

Out of curiosity, is UEFI not always single threaded instead of just default single threaded?

You technically could implement a form of multithreading, just like with wasm. It's just builtin.single_threaded will default to true when single_threaded is not changed in your build. You probably could write a custom scheduler + mutltithreading stuff and use root.os stuff to get it working but no implementation will be made for upstream.

I learned somewhat recently that UEFI does have EFI_MP_SERVICES_PROTOCOL so there is a way to do multiprocessing but not multithreading but likely is still out of the scope.

linusg · 2024-12-19T11:08:15Z

lib/std/fs.zig

@@ -52,7 +52,7 @@ pub const MAX_PATH_BYTES = @compileError("deprecated; renamed to max_path_bytes"
 /// * On other platforms, `[]u8` file paths are opaque sequences of bytes with
 ///   no particular encoding.
 pub const max_path_bytes = switch (native_os) {
-    .linux, .macos, .ios, .freebsd, .openbsd, .netbsd, .dragonfly, .haiku, .solaris, .illumos, .plan9, .emscripten, .wasi => posix.PATH_MAX,
+    .linux, .macos, .ios, .freebsd, .openbsd, .netbsd, .dragonfly, .haiku, .solaris, .illumos, .plan9, .emscripten, .wasi, .uefi => posix.PATH_MAX,


This looks wrong, I'd assume it needs to use similar logic as windows

I think this ties in with #22226 (comment)

linusg · 2024-12-19T11:10:15Z

lib/std/fs/Dir.zig

+
+        pub fn next(self: *Self) Error!?Entry {
+            _ = self;
+            return null;


Not sure if turning a compile error into a non-functional stub is that useful? Most people will assume the standard library functions work for a certain target if they compile.

Yeah, I hadn't figured out how to implement it just yet. I'll leave it out of this PR and work on it later on.

linusg · 2024-12-19T11:13:49Z

lib/std/os/uefi/allocator.zig

+/// Allocates memory in pages.
+///
+/// This allocator is backed by `allocatePages` and is therefore only suitable for usage when Boot Services are available.
+pub const PageAllocator = struct {


std.os.uefi.allocator.{Page,Pool}Allocator violates https://ziglang.org/documentation/master/#Avoid-Redundant-Names-in-Fully-Qualified-Namespaces

I have changed it now, hopefully it doesn't violate the fully qualified namespace stuff.

linusg · 2024-12-19T11:16:26Z

lib/std/start.zig

+                if (@errorReturnTrace()) |trace| {
+                    std.debug.dumpStackTrace(trace.*);
+                }
+                std.time.sleep(5 * std.time.ns_per_s);


Magic sleep needs a comment

This part of the code is based on what @truemedian did. I'm not sure either so CC'ing them for some information.

Magic sleep here was a debugging aid to prevent the uefi firmware from clearing the screen before I could read the any output because once EfiMain returns it will go to the next boot loader. Not necessary at all, unless that window to eead the error is desired.

Ok, I likely will remove it and it'll be up to the program to do that if they want to.

alexrp reviewed Dec 13, 2024

View reviewed changes

RossComputerGuy force-pushed the feat/uefi-zig-init branch from 87beafb to 2a2c072 Compare December 13, 2024 23:02

linusg reviewed Dec 19, 2024

View reviewed changes

RossComputerGuy force-pushed the feat/uefi-zig-init branch from 2a2c072 to cb18f91 Compare December 19, 2024 19:05

std: implement basic io and improve alloc in uefi

74b7013

RossComputerGuy force-pushed the feat/uefi-zig-init branch from cb18f91 to 74b7013 Compare December 19, 2024 19:09

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std: implement basic io and improve alloc in uefi #22226

std: implement basic io and improve alloc in uefi #22226

RossComputerGuy commented Dec 13, 2024

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linusg Dec 19, 2024 •

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truemedian Dec 19, 2024

RossComputerGuy Dec 29, 2024

		@@ -1,5 +1,7 @@
		const std = @import("../std.zig");

		pub const posix = @import("uefi/posix.zig");

	pub fn alwaysSingleThreaded(target: std.Target) bool {
	_ = target;
	return false;
	}

	pub fn defaultSingleThreaded(target: std.Target) bool {
	switch (target.cpu.arch) {
	.wasm32, .wasm64 => return true,
	else => {},
	}
	switch (target.os.tag) {
	.haiku => return true,
	else => {},
	}
	return false;
	}

std: implement basic io and improve alloc in uefi #22226

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std: implement basic io and improve alloc in uefi #22226

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RossComputerGuy commented Dec 13, 2024

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linusg Dec 19, 2024 • edited Loading

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linusg Dec 19, 2024 •

edited

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