diff --git a/build.zig b/build.zig
index 7208d1fbb9..401f46ff1e 100644
--- a/build.zig
+++ b/build.zig
@@ -81,12 +81,13 @@ pub fn build(b: *std.Build) !void {
     docs_step.dependOn(langref_step);
     docs_step.dependOn(std_docs_step);
 
+    const test_default_only = b.option(bool, "test-default-only", "Limit test matrix to exactly one target configuration") orelse false;
     const skip_debug = b.option(bool, "skip-debug", "Main test suite skips debug builds") orelse false;
-    const skip_release = b.option(bool, "skip-release", "Main test suite skips release builds") orelse false;
+    const skip_release = b.option(bool, "skip-release", "Main test suite skips release builds") orelse test_default_only;
     const skip_release_small = b.option(bool, "skip-release-small", "Main test suite skips release-small builds") orelse skip_release;
     const skip_release_fast = b.option(bool, "skip-release-fast", "Main test suite skips release-fast builds") orelse skip_release;
     const skip_release_safe = b.option(bool, "skip-release-safe", "Main test suite skips release-safe builds") orelse skip_release;
-    const skip_non_native = b.option(bool, "skip-non-native", "Main test suite skips non-native builds") orelse false;
+    const skip_non_native = b.option(bool, "skip-non-native", "Main test suite skips non-native builds") orelse test_default_only;
     const skip_libc = b.option(bool, "skip-libc", "Main test suite skips tests that link libc") orelse false;
     const skip_single_threaded = b.option(bool, "skip-single-threaded", "Main test suite skips tests that are single-threaded") orelse false;
     const skip_compile_errors = b.option(bool, "skip-compile-errors", "Main test suite skips compile error tests") orelse false;
@@ -449,6 +450,7 @@ pub fn build(b: *std.Build) !void {
         .include_paths = &.{},
         .skip_single_threaded = skip_single_threaded,
         .skip_non_native = skip_non_native,
+        .test_default_only = test_default_only,
         .skip_freebsd = skip_freebsd,
         .skip_netbsd = skip_netbsd,
         .skip_windows = skip_windows,
@@ -471,6 +473,7 @@ pub fn build(b: *std.Build) !void {
         .include_paths = &.{},
         .skip_single_threaded = true,
         .skip_non_native = skip_non_native,
+        .test_default_only = test_default_only,
         .skip_freebsd = skip_freebsd,
         .skip_netbsd = skip_netbsd,
         .skip_windows = skip_windows,
@@ -492,6 +495,7 @@ pub fn build(b: *std.Build) !void {
         .include_paths = &.{},
         .skip_single_threaded = true,
         .skip_non_native = skip_non_native,
+        .test_default_only = test_default_only,
         .skip_freebsd = skip_freebsd,
         .skip_netbsd = skip_netbsd,
         .skip_windows = skip_windows,
@@ -513,6 +517,7 @@ pub fn build(b: *std.Build) !void {
         .include_paths = &.{},
         .skip_single_threaded = skip_single_threaded,
         .skip_non_native = skip_non_native,
+        .test_default_only = test_default_only,
         .skip_freebsd = skip_freebsd,
         .skip_netbsd = skip_netbsd,
         .skip_windows = skip_windows,
diff --git a/lib/std/Io/Reader.zig b/lib/std/Io/Reader.zig
index 8a01dc9a9d..e2344e959e 100644
--- a/lib/std/Io/Reader.zig
+++ b/lib/std/Io/Reader.zig
@@ -481,7 +481,6 @@ pub fn readVecAll(r: *Reader, data: [][]u8) Error!void {
 /// is returned instead.
 ///
 /// See also:
-/// * `peek`
 /// * `toss`
 pub fn peek(r: *Reader, n: usize) Error![]u8 {
     try r.fill(n);
@@ -732,7 +731,7 @@ pub const DelimiterError = error{
 };
 
 /// Returns a slice of the next bytes of buffered data from the stream until
-/// `sentinel` is found, advancing the seek position.
+/// `sentinel` is found, advancing the seek position past the sentinel.
 ///
 /// Returned slice has a sentinel.
 ///
@@ -765,7 +764,7 @@ pub fn peekSentinel(r: *Reader, comptime sentinel: u8) DelimiterError![:sentinel
 }
 
 /// Returns a slice of the next bytes of buffered data from the stream until
-/// `delimiter` is found, advancing the seek position.
+/// `delimiter` is found, advancing the seek position past the delimiter.
 ///
 /// Returned slice includes the delimiter as the last byte.
 ///
@@ -793,32 +792,42 @@ pub fn takeDelimiterInclusive(r: *Reader, delimiter: u8) DelimiterError![]u8 {
 /// * `peekDelimiterExclusive`
 /// * `takeDelimiterInclusive`
 pub fn peekDelimiterInclusive(r: *Reader, delimiter: u8) DelimiterError![]u8 {
-    const buffer = r.buffer[0..r.end];
-    const seek = r.seek;
-    if (std.mem.indexOfScalarPos(u8, buffer, seek, delimiter)) |delimiter_index| {
-        @branchHint(.likely);
-        return buffer[seek .. delimiter_index + 1];
-    }
-    // TODO take a parameter for max search length rather than relying on buffer capacity
-    try rebase(r, r.buffer.len);
-    while (r.buffer.len - r.end != 0) {
-        const existing_buffered_len = r.end - r.seek;
-        const end_cap = r.buffer[r.end..];
-        var writer: Writer = .fixed(end_cap);
-        const n = r.vtable.stream(r, &writer, .limited(end_cap.len)) catch |err| switch (err) {
-            error.WriteFailed => unreachable,
-            else => |e| return e,
-        };
-        r.end += n;
-        if (std.mem.indexOfScalarPos(u8, r.buffer[0..r.end], r.seek + existing_buffered_len, delimiter)) |delimiter_index| {
-            return r.buffer[r.seek .. delimiter_index + 1];
+    {
+        const contents = r.buffer[0..r.end];
+        const seek = r.seek;
+        if (std.mem.findScalarPos(u8, contents, seek, delimiter)) |end| {
+            @branchHint(.likely);
+            return contents[seek .. end + 1];
         }
     }
-    return error.StreamTooLong;
+    while (true) {
+        const content_len = r.end - r.seek;
+        if (r.buffer.len - content_len == 0) break;
+        try fillMore(r);
+        const seek = r.seek;
+        const contents = r.buffer[0..r.end];
+        if (std.mem.findScalarPos(u8, contents, seek + content_len, delimiter)) |end| {
+            return contents[seek .. end + 1];
+        }
+    }
+    // It might or might not be end of stream. There is no more buffer space
+    // left to disambiguate. If `StreamTooLong` was added to `RebaseError` then
+    // this logic could be replaced by removing the exit condition from the
+    // above while loop. That error code would represent when `buffer` capacity
+    // is too small for an operation, replacing the current use of asserts.
+    var failing_writer = Writer.failing;
+    while (r.vtable.stream(r, &failing_writer, .limited(1))) |n| {
+        assert(n == 0);
+    } else |err| switch (err) {
+        error.WriteFailed => return error.StreamTooLong,
+        error.ReadFailed => |e| return e,
+        error.EndOfStream => |e| return e,
+    }
 }
 
 /// Returns a slice of the next bytes of buffered data from the stream until
-/// `delimiter` is found, advancing the seek position up to the delimiter.
+/// `delimiter` is found, advancing the seek position up to (but not past)
+/// the delimiter.
 ///
 /// Returned slice excludes the delimiter. End-of-stream is treated equivalent
 /// to a delimiter, unless it would result in a length 0 return value, in which
@@ -832,20 +841,13 @@ pub fn peekDelimiterInclusive(r: *Reader, delimiter: u8) DelimiterError![]u8 {
 /// Invalidates previously returned values from `peek`.
 ///
 /// See also:
+/// * `takeDelimiter`
 /// * `takeDelimiterInclusive`
 /// * `peekDelimiterExclusive`
 pub fn takeDelimiterExclusive(r: *Reader, delimiter: u8) DelimiterError![]u8 {
-    const result = r.peekDelimiterInclusive(delimiter) catch |err| switch (err) {
-        error.EndOfStream => {
-            const remaining = r.buffer[r.seek..r.end];
-            if (remaining.len == 0) return error.EndOfStream;
-            r.toss(remaining.len);
-            return remaining;
-        },
-        else => |e| return e,
-    };
+    const result = try r.peekDelimiterExclusive(delimiter);
     r.toss(result.len);
-    return result[0 .. result.len - 1];
+    return result;
 }
 
 /// Returns a slice of the next bytes of buffered data from the stream until
@@ -866,7 +868,7 @@ pub fn takeDelimiterExclusive(r: *Reader, delimiter: u8) DelimiterError![]u8 {
 /// * `takeDelimiterInclusive`
 /// * `takeDelimiterExclusive`
 pub fn takeDelimiter(r: *Reader, delimiter: u8) error{ ReadFailed, StreamTooLong }!?[]u8 {
-    const result = r.peekDelimiterInclusive(delimiter) catch |err| switch (err) {
+    const inclusive = r.peekDelimiterInclusive(delimiter) catch |err| switch (err) {
         error.EndOfStream => {
             const remaining = r.buffer[r.seek..r.end];
             if (remaining.len == 0) return null;
@@ -875,8 +877,8 @@ pub fn takeDelimiter(r: *Reader, delimiter: u8) error{ ReadFailed, StreamTooLong
         },
         else => |e| return e,
     };
-    r.toss(result.len + 1);
-    return result[0 .. result.len - 1];
+    r.toss(inclusive.len);
+    return inclusive[0 .. inclusive.len - 1];
 }
 
 /// Returns a slice of the next bytes of buffered data from the stream until
@@ -1403,6 +1405,9 @@ test peekSentinel {
     var r: Reader = .fixed("ab\nc");
     try testing.expectEqualStrings("ab", try r.peekSentinel('\n'));
     try testing.expectEqualStrings("ab", try r.peekSentinel('\n'));
+    r.toss(3);
+    try testing.expectError(error.EndOfStream, r.peekSentinel('\n'));
+    try testing.expectEqualStrings("c", try r.peek(1));
 }
 
 test takeDelimiterInclusive {
@@ -1417,22 +1422,52 @@ test peekDelimiterInclusive {
     try testing.expectEqualStrings("ab\n", try r.peekDelimiterInclusive('\n'));
     r.toss(3);
     try testing.expectError(error.EndOfStream, r.peekDelimiterInclusive('\n'));
+    try testing.expectEqualStrings("c", try r.peek(1));
 }
 
 test takeDelimiterExclusive {
     var r: Reader = .fixed("ab\nc");
+
     try testing.expectEqualStrings("ab", try r.takeDelimiterExclusive('\n'));
+    try testing.expectEqualStrings("", try r.takeDelimiterExclusive('\n'));
+    try testing.expectEqualStrings("", try r.takeDelimiterExclusive('\n'));
+    try testing.expectEqualStrings("\n", try r.take(1));
+
     try testing.expectEqualStrings("c", try r.takeDelimiterExclusive('\n'));
     try testing.expectError(error.EndOfStream, r.takeDelimiterExclusive('\n'));
 }
 
 test peekDelimiterExclusive {
     var r: Reader = .fixed("ab\nc");
+
     try testing.expectEqualStrings("ab", try r.peekDelimiterExclusive('\n'));
     try testing.expectEqualStrings("ab", try r.peekDelimiterExclusive('\n'));
-    r.toss(3);
+    r.toss(2);
+    try testing.expectEqualStrings("", try r.peekDelimiterExclusive('\n'));
+    try testing.expectEqualStrings("\n", try r.take(1));
+
     try testing.expectEqualStrings("c", try r.peekDelimiterExclusive('\n'));
     try testing.expectEqualStrings("c", try r.peekDelimiterExclusive('\n'));
+    r.toss(1);
+    try testing.expectError(error.EndOfStream, r.peekDelimiterExclusive('\n'));
+}
+
+test takeDelimiter {
+    var r: Reader = .fixed("ab\nc\n\nd");
+    try testing.expectEqualStrings("ab", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqualStrings("c", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqualStrings("", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqualStrings("d", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqual(null, try r.takeDelimiter('\n'));
+    try testing.expectEqual(null, try r.takeDelimiter('\n'));
+
+    r = .fixed("ab\nc\n\nd\n"); // one trailing newline does not affect behavior
+    try testing.expectEqualStrings("ab", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqualStrings("c", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqualStrings("", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqualStrings("d", (try r.takeDelimiter('\n')).?);
+    try testing.expectEqual(null, try r.takeDelimiter('\n'));
+    try testing.expectEqual(null, try r.takeDelimiter('\n'));
 }
 
 test streamDelimiter {
diff --git a/lib/std/Io/Reader/Limited.zig b/lib/std/Io/Reader/Limited.zig
index e0d04bb531..d983133307 100644
--- a/lib/std/Io/Reader/Limited.zig
+++ b/lib/std/Io/Reader/Limited.zig
@@ -27,6 +27,7 @@ pub fn init(reader: *Reader, limit: Limit, buffer: []u8) Limited {
 
 fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
     const l: *Limited = @fieldParentPtr("interface", r);
+    if (l.remaining == .nothing) return error.EndOfStream;
     const combined_limit = limit.min(l.remaining);
     const n = try l.unlimited.stream(w, combined_limit);
     l.remaining = l.remaining.subtract(n).?;
@@ -51,8 +52,51 @@ test stream {
 
 fn discard(r: *Reader, limit: Limit) Reader.Error!usize {
     const l: *Limited = @fieldParentPtr("interface", r);
+    if (l.remaining == .nothing) return error.EndOfStream;
     const combined_limit = limit.min(l.remaining);
     const n = try l.unlimited.discard(combined_limit);
     l.remaining = l.remaining.subtract(n).?;
     return n;
 }
+
+test "end of stream, read, hit limit exactly" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(4), &.{});
+    const r = &l.interface;
+
+    var buf: [2]u8 = undefined;
+    try r.readSliceAll(&buf);
+    try r.readSliceAll(&buf);
+    try std.testing.expectError(error.EndOfStream, l.interface.readSliceAll(&buf));
+}
+
+test "end of stream, read, hit limit after partial read" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(5), &.{});
+    const r = &l.interface;
+
+    var buf: [2]u8 = undefined;
+    try r.readSliceAll(&buf);
+    try r.readSliceAll(&buf);
+    try std.testing.expectError(error.EndOfStream, l.interface.readSliceAll(&buf));
+}
+
+test "end of stream, discard, hit limit exactly" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(4), &.{});
+    const r = &l.interface;
+
+    try r.discardAll(2);
+    try r.discardAll(2);
+    try std.testing.expectError(error.EndOfStream, l.interface.discardAll(2));
+}
+
+test "end of stream, discard, hit limit after partial read" {
+    var f: Reader = .fixed("i'm dying");
+    var l = f.limited(.limited(5), &.{});
+    const r = &l.interface;
+
+    try r.discardAll(2);
+    try r.discardAll(2);
+    try std.testing.expectError(error.EndOfStream, l.interface.discardAll(2));
+}
diff --git a/lib/std/Io/Writer.zig b/lib/std/Io/Writer.zig
index 77383ae278..7ad466d5cb 100644
--- a/lib/std/Io/Writer.zig
+++ b/lib/std/Io/Writer.zig
@@ -923,10 +923,12 @@ pub fn sendFileHeader(
     return n;
 }
 
-/// Asserts nonzero buffer capacity.
+/// Asserts nonzero buffer capacity and nonzero `limit`.
 pub fn sendFileReading(w: *Writer, file_reader: *File.Reader, limit: Limit) FileReadingError!usize {
+    assert(limit != .nothing);
     const dest = limit.slice(try w.writableSliceGreedy(1));
-    const n = try file_reader.read(dest);
+    const n = try file_reader.interface.readSliceShort(dest);
+    if (n == 0) return error.EndOfStream;
     w.advance(n);
     return n;
 }
@@ -2778,7 +2780,8 @@ pub const Allocating = struct {
         if (additional == 0) return error.EndOfStream;
         a.ensureUnusedCapacity(limit.minInt64(additional)) catch return error.WriteFailed;
         const dest = limit.slice(a.writer.buffer[a.writer.end..]);
-        const n = try file_reader.read(dest);
+        const n = try file_reader.interface.readSliceShort(dest);
+        if (n == 0) return error.EndOfStream;
         a.writer.end += n;
         return n;
     }
@@ -2849,18 +2852,40 @@ test "allocating sendFile" {
 
     const file = try tmp_dir.dir.createFile("input.txt", .{ .read = true });
     defer file.close();
-    var r_buffer: [256]u8 = undefined;
+    var r_buffer: [2]u8 = undefined;
     var file_writer: std.fs.File.Writer = .init(file, &r_buffer);
-    try file_writer.interface.writeByte('h');
+    try file_writer.interface.writeAll("abcd");
     try file_writer.interface.flush();
 
     var file_reader = file_writer.moveToReader();
     try file_reader.seekTo(0);
+    try file_reader.interface.fill(2);
 
     var allocating: Writer.Allocating = .init(testing.allocator);
     defer allocating.deinit();
+    try allocating.ensureUnusedCapacity(1);
+    try testing.expectEqual(4, allocating.writer.sendFileAll(&file_reader, .unlimited));
+    try testing.expectEqualStrings("abcd", allocating.writer.buffered());
+}
 
-    _ = try file_reader.interface.streamRemaining(&allocating.writer);
+test sendFileReading {
+    var tmp_dir = testing.tmpDir(.{});
+    defer tmp_dir.cleanup();
+
+    const file = try tmp_dir.dir.createFile("input.txt", .{ .read = true });
+    defer file.close();
+    var r_buffer: [2]u8 = undefined;
+    var file_writer: std.fs.File.Writer = .init(file, &r_buffer);
+    try file_writer.interface.writeAll("abcd");
+    try file_writer.interface.flush();
+
+    var file_reader = file_writer.moveToReader();
+    try file_reader.seekTo(0);
+    try file_reader.interface.fill(2);
+
+    var w_buffer: [1]u8 = undefined;
+    var discarding: Writer.Discarding = .init(&w_buffer);
+    try testing.expectEqual(4, discarding.writer.sendFileReadingAll(&file_reader, .unlimited));
 }
 
 test writeStruct {
diff --git a/lib/std/fs/File.zig b/lib/std/fs/File.zig
index 99dda27885..05b423967d 100644
--- a/lib/std/fs/File.zig
+++ b/lib/std/fs/File.zig
@@ -1189,7 +1189,7 @@ pub const Reader = struct {
     pub fn seekBy(r: *Reader, offset: i64) Reader.SeekError!void {
         switch (r.mode) {
             .positional, .positional_reading => {
-                setPosAdjustingBuffer(r, @intCast(@as(i64, @intCast(r.pos)) + offset));
+                setLogicalPos(r, @intCast(@as(i64, @intCast(logicalPos(r))) + offset));
             },
             .streaming, .streaming_reading => {
                 if (posix.SEEK == void) {
@@ -1198,7 +1198,7 @@ pub const Reader = struct {
                 }
                 const seek_err = r.seek_err orelse e: {
                     if (posix.lseek_CUR(r.file.handle, offset)) |_| {
-                        setPosAdjustingBuffer(r, @intCast(@as(i64, @intCast(r.pos)) + offset));
+                        setLogicalPos(r, @intCast(@as(i64, @intCast(logicalPos(r))) + offset));
                         return;
                     } else |err| {
                         r.seek_err = err;
@@ -1222,16 +1222,16 @@ pub const Reader = struct {
     pub fn seekTo(r: *Reader, offset: u64) Reader.SeekError!void {
         switch (r.mode) {
             .positional, .positional_reading => {
-                setPosAdjustingBuffer(r, offset);
+                setLogicalPos(r, offset);
             },
             .streaming, .streaming_reading => {
-                if (offset >= r.pos) return Reader.seekBy(r, @intCast(offset - r.pos));
+                if (offset >= r.pos) return Reader.seekBy(r, @intCast(offset - logicalPos(r)));
                 if (r.seek_err) |err| return err;
                 posix.lseek_SET(r.file.handle, offset) catch |err| {
                     r.seek_err = err;
                     return err;
                 };
-                setPosAdjustingBuffer(r, offset);
+                setLogicalPos(r, offset);
             },
             .failure => return r.seek_err.?,
         }
@@ -1241,7 +1241,7 @@ pub const Reader = struct {
         return r.pos - r.interface.bufferedLen();
     }
 
-    fn setPosAdjustingBuffer(r: *Reader, offset: u64) void {
+    fn setLogicalPos(r: *Reader, offset: u64) void {
         const logical_pos = logicalPos(r);
         if (offset < logical_pos or offset >= r.pos) {
             r.interface.seek = 0;
@@ -1269,13 +1269,15 @@ pub const Reader = struct {
             },
             .positional_reading => {
                 const dest = limit.slice(try w.writableSliceGreedy(1));
-                const n = try readPositional(r, dest);
+                var data: [1][]u8 = .{dest};
+                const n = try readVecPositional(r, &data);
                 w.advance(n);
                 return n;
             },
             .streaming_reading => {
                 const dest = limit.slice(try w.writableSliceGreedy(1));
-                const n = try readStreaming(r, dest);
+                var data: [1][]u8 = .{dest};
+                const n = try readVecStreaming(r, &data);
                 w.advance(n);
                 return n;
             },
@@ -1286,94 +1288,100 @@ pub const Reader = struct {
     fn readVec(io_reader: *std.Io.Reader, data: [][]u8) std.Io.Reader.Error!usize {
         const r: *Reader = @alignCast(@fieldParentPtr("interface", io_reader));
         switch (r.mode) {
-            .positional, .positional_reading => {
-                if (is_windows) {
-                    // Unfortunately, `ReadFileScatter` cannot be used since it
-                    // requires page alignment.
-                    if (io_reader.seek == io_reader.end) {
-                        io_reader.seek = 0;
-                        io_reader.end = 0;
-                    }
-                    const first = data[0];
-                    if (first.len >= io_reader.buffer.len - io_reader.end) {
-                        return readPositional(r, first);
-                    } else {
-                        io_reader.end += try readPositional(r, io_reader.buffer[io_reader.end..]);
-                        return 0;
-                    }
-                }
-                var iovecs_buffer: [max_buffers_len]posix.iovec = undefined;
-                const dest_n, const data_size = try io_reader.writableVectorPosix(&iovecs_buffer, data);
-                const dest = iovecs_buffer[0..dest_n];
-                assert(dest[0].len > 0);
-                const n = posix.preadv(r.file.handle, dest, r.pos) catch |err| switch (err) {
-                    error.Unseekable => {
-                        r.mode = r.mode.toStreaming();
-                        const pos = r.pos;
-                        if (pos != 0) {
-                            r.pos = 0;
-                            r.seekBy(@intCast(pos)) catch {
-                                r.mode = .failure;
-                                return error.ReadFailed;
-                            };
-                        }
-                        return 0;
-                    },
-                    else => |e| {
-                        r.err = e;
-                        return error.ReadFailed;
-                    },
-                };
-                if (n == 0) {
-                    r.size = r.pos;
-                    return error.EndOfStream;
-                }
-                r.pos += n;
-                if (n > data_size) {
-                    io_reader.end += n - data_size;
-                    return data_size;
-                }
-                return n;
-            },
-            .streaming, .streaming_reading => {
-                if (is_windows) {
-                    // Unfortunately, `ReadFileScatter` cannot be used since it
-                    // requires page alignment.
-                    if (io_reader.seek == io_reader.end) {
-                        io_reader.seek = 0;
-                        io_reader.end = 0;
-                    }
-                    const first = data[0];
-                    if (first.len >= io_reader.buffer.len - io_reader.end) {
-                        return readStreaming(r, first);
-                    } else {
-                        io_reader.end += try readStreaming(r, io_reader.buffer[io_reader.end..]);
-                        return 0;
-                    }
-                }
-                var iovecs_buffer: [max_buffers_len]posix.iovec = undefined;
-                const dest_n, const data_size = try io_reader.writableVectorPosix(&iovecs_buffer, data);
-                const dest = iovecs_buffer[0..dest_n];
-                assert(dest[0].len > 0);
-                const n = posix.readv(r.file.handle, dest) catch |err| {
-                    r.err = err;
-                    return error.ReadFailed;
-                };
-                if (n == 0) {
-                    r.size = r.pos;
-                    return error.EndOfStream;
-                }
-                r.pos += n;
-                if (n > data_size) {
-                    io_reader.end += n - data_size;
-                    return data_size;
-                }
-                return n;
-            },
+            .positional, .positional_reading => return readVecPositional(r, data),
+            .streaming, .streaming_reading => return readVecStreaming(r, data),
             .failure => return error.ReadFailed,
         }
     }
 
+    fn readVecPositional(r: *Reader, data: [][]u8) std.Io.Reader.Error!usize {
+        const io_reader = &r.interface;
+        if (is_windows) {
+            // Unfortunately, `ReadFileScatter` cannot be used since it
+            // requires page alignment.
+            if (io_reader.seek == io_reader.end) {
+                io_reader.seek = 0;
+                io_reader.end = 0;
+            }
+            const first = data[0];
+            if (first.len >= io_reader.buffer.len - io_reader.end) {
+                return readPositional(r, first);
+            } else {
+                io_reader.end += try readPositional(r, io_reader.buffer[io_reader.end..]);
+                return 0;
+            }
+        }
+        var iovecs_buffer: [max_buffers_len]posix.iovec = undefined;
+        const dest_n, const data_size = try io_reader.writableVectorPosix(&iovecs_buffer, data);
+        const dest = iovecs_buffer[0..dest_n];
+        assert(dest[0].len > 0);
+        const n = posix.preadv(r.file.handle, dest, r.pos) catch |err| switch (err) {
+            error.Unseekable => {
+                r.mode = r.mode.toStreaming();
+                const pos = r.pos;
+                if (pos != 0) {
+                    r.pos = 0;
+                    r.seekBy(@intCast(pos)) catch {
+                        r.mode = .failure;
+                        return error.ReadFailed;
+                    };
+                }
+                return 0;
+            },
+            else => |e| {
+                r.err = e;
+                return error.ReadFailed;
+            },
+        };
+        if (n == 0) {
+            r.size = r.pos;
+            return error.EndOfStream;
+        }
+        r.pos += n;
+        if (n > data_size) {
+            io_reader.end += n - data_size;
+            return data_size;
+        }
+        return n;
+    }
+
+    fn readVecStreaming(r: *Reader, data: [][]u8) std.Io.Reader.Error!usize {
+        const io_reader = &r.interface;
+        if (is_windows) {
+            // Unfortunately, `ReadFileScatter` cannot be used since it
+            // requires page alignment.
+            if (io_reader.seek == io_reader.end) {
+                io_reader.seek = 0;
+                io_reader.end = 0;
+            }
+            const first = data[0];
+            if (first.len >= io_reader.buffer.len - io_reader.end) {
+                return readStreaming(r, first);
+            } else {
+                io_reader.end += try readStreaming(r, io_reader.buffer[io_reader.end..]);
+                return 0;
+            }
+        }
+        var iovecs_buffer: [max_buffers_len]posix.iovec = undefined;
+        const dest_n, const data_size = try io_reader.writableVectorPosix(&iovecs_buffer, data);
+        const dest = iovecs_buffer[0..dest_n];
+        assert(dest[0].len > 0);
+        const n = posix.readv(r.file.handle, dest) catch |err| {
+            r.err = err;
+            return error.ReadFailed;
+        };
+        if (n == 0) {
+            r.size = r.pos;
+            return error.EndOfStream;
+        }
+        r.pos += n;
+        if (n > data_size) {
+            io_reader.end += n - data_size;
+            return data_size;
+        }
+        return n;
+    }
+
     fn discard(io_reader: *std.Io.Reader, limit: std.Io.Limit) std.Io.Reader.Error!usize {
         const r: *Reader = @alignCast(@fieldParentPtr("interface", io_reader));
         const file = r.file;
@@ -1440,7 +1448,7 @@ pub const Reader = struct {
         }
     }
 
-    pub fn readPositional(r: *Reader, dest: []u8) std.Io.Reader.Error!usize {
+    fn readPositional(r: *Reader, dest: []u8) std.Io.Reader.Error!usize {
         const n = r.file.pread(dest, r.pos) catch |err| switch (err) {
             error.Unseekable => {
                 r.mode = r.mode.toStreaming();
@@ -1467,7 +1475,7 @@ pub const Reader = struct {
         return n;
     }
 
-    pub fn readStreaming(r: *Reader, dest: []u8) std.Io.Reader.Error!usize {
+    fn readStreaming(r: *Reader, dest: []u8) std.Io.Reader.Error!usize {
         const n = r.file.read(dest) catch |err| {
             r.err = err;
             return error.ReadFailed;
@@ -1480,14 +1488,6 @@ pub const Reader = struct {
         return n;
     }
 
-    pub fn read(r: *Reader, dest: []u8) std.Io.Reader.Error!usize {
-        switch (r.mode) {
-            .positional, .positional_reading => return readPositional(r, dest),
-            .streaming, .streaming_reading => return readStreaming(r, dest),
-            .failure => return error.ReadFailed,
-        }
-    }
-
     pub fn atEnd(r: *Reader) bool {
         // Even if stat fails, size is set when end is encountered.
         const size = r.size orelse return false;
@@ -1732,7 +1732,7 @@ pub const Writer = struct {
     ) std.Io.Writer.FileError!usize {
         const reader_buffered = file_reader.interface.buffered();
         if (reader_buffered.len >= @intFromEnum(limit))
-            return sendFileBuffered(io_w, file_reader, reader_buffered);
+            return sendFileBuffered(io_w, file_reader, limit.slice(reader_buffered));
         const writer_buffered = io_w.buffered();
         const file_limit = @intFromEnum(limit) - reader_buffered.len;
         const w: *Writer = @alignCast(@fieldParentPtr("interface", io_w));
@@ -1804,7 +1804,7 @@ pub const Writer = struct {
                 return error.EndOfStream;
             }
             const consumed = io_w.consume(@intCast(sbytes));
-            file_reader.seekTo(file_reader.pos + consumed) catch return error.ReadFailed;
+            file_reader.seekBy(@intCast(consumed)) catch return error.ReadFailed;
             return consumed;
         }
 
@@ -1865,7 +1865,7 @@ pub const Writer = struct {
                 return error.EndOfStream;
             }
             const consumed = io_w.consume(@bitCast(len));
-            file_reader.seekTo(file_reader.pos + consumed) catch return error.ReadFailed;
+            file_reader.seekBy(@intCast(consumed)) catch return error.ReadFailed;
             return consumed;
         }
 
@@ -1998,7 +1998,7 @@ pub const Writer = struct {
         reader_buffered: []const u8,
     ) std.Io.Writer.FileError!usize {
         const n = try drain(io_w, &.{reader_buffered}, 1);
-        file_reader.seekTo(file_reader.pos + n) catch return error.ReadFailed;
+        file_reader.seekBy(@intCast(n)) catch return error.ReadFailed;
         return n;
     }
 
diff --git a/lib/std/fs/test.zig b/lib/std/fs/test.zig
index b88456ef7c..0949d71a2d 100644
--- a/lib/std/fs/test.zig
+++ b/lib/std/fs/test.zig
@@ -1525,6 +1525,41 @@ test "sendfile" {
     try testing.expectEqualStrings("header1\nsecond header\nine1\nsecontrailer1\nsecond trailer\n", written_buf[0..amt]);
 }
 
+test "sendfile with buffered data" {
+    var tmp = tmpDir(.{});
+    defer tmp.cleanup();
+
+    try tmp.dir.makePath("os_test_tmp");
+
+    var dir = try tmp.dir.openDir("os_test_tmp", .{});
+    defer dir.close();
+
+    var src_file = try dir.createFile("sendfile1.txt", .{ .read = true });
+    defer src_file.close();
+
+    try src_file.writeAll("AAAABBBB");
+
+    var dest_file = try dir.createFile("sendfile2.txt", .{ .read = true });
+    defer dest_file.close();
+
+    var src_buffer: [32]u8 = undefined;
+    var file_reader = src_file.reader(&src_buffer);
+
+    try file_reader.seekTo(0);
+    try file_reader.interface.fill(8);
+
+    var fallback_buffer: [32]u8 = undefined;
+    var file_writer = dest_file.writer(&fallback_buffer);
+
+    try std.testing.expectEqual(4, try file_writer.interface.sendFileAll(&file_reader, .limited(4)));
+
+    var written_buf: [8]u8 = undefined;
+    const amt = try dest_file.preadAll(&written_buf, 0);
+
+    try std.testing.expectEqual(4, amt);
+    try std.testing.expectEqualSlices(u8, "AAAA", written_buf[0..amt]);
+}
+
 test "copyRangeAll" {
     var tmp = tmpDir(.{});
     defer tmp.cleanup();
@@ -2250,3 +2285,34 @@ test "seekTo flushes buffered data" {
     try file_reader.interface.readSliceAll(&buf);
     try std.testing.expectEqualStrings(contents, &buf);
 }
+
+test "File.Writer sendfile with buffered contents" {
+    var tmp_dir = testing.tmpDir(.{});
+    defer tmp_dir.cleanup();
+
+    {
+        try tmp_dir.dir.writeFile(.{ .sub_path = "a", .data = "bcd" });
+        const in = try tmp_dir.dir.openFile("a", .{});
+        defer in.close();
+        const out = try tmp_dir.dir.createFile("b", .{});
+        defer out.close();
+
+        var in_buf: [2]u8 = undefined;
+        var in_r = in.reader(&in_buf);
+        _ = try in_r.getSize(); // Catch seeks past end by populating size
+        try in_r.interface.fill(2);
+
+        var out_buf: [1]u8 = undefined;
+        var out_w = out.writerStreaming(&out_buf);
+        try out_w.interface.writeByte('a');
+        try testing.expectEqual(3, try out_w.interface.sendFileAll(&in_r, .unlimited));
+        try out_w.interface.flush();
+    }
+
+    var check = try tmp_dir.dir.openFile("b", .{});
+    defer check.close();
+    var check_buf: [4]u8 = undefined;
+    var check_r = check.reader(&check_buf);
+    try testing.expectEqualStrings("abcd", try check_r.interface.take(4));
+    try testing.expectError(error.EndOfStream, check_r.interface.takeByte());
+}
diff --git a/lib/std/net.zig b/lib/std/net.zig
index 37fe2734d5..9d70515c2e 100644
--- a/lib/std/net.zig
+++ b/lib/std/net.zig
@@ -1396,7 +1396,7 @@ fn parseHosts(
     br: *Io.Reader,
 ) error{ OutOfMemory, ReadFailed }!void {
     while (true) {
-        const line = br.takeDelimiterExclusive('\n') catch |err| switch (err) {
+        const line = br.takeDelimiter('\n') catch |err| switch (err) {
             error.StreamTooLong => {
                 // Skip lines that are too long.
                 _ = br.discardDelimiterInclusive('\n') catch |e| switch (e) {
@@ -1406,7 +1406,8 @@ fn parseHosts(
                 continue;
             },
             error.ReadFailed => return error.ReadFailed,
-            error.EndOfStream => break,
+        } orelse {
+            break; // end of stream
         };
         var split_it = mem.splitScalar(u8, line, '#');
         const no_comment_line = split_it.first();
diff --git a/lib/std/zig/system/linux.zig b/lib/std/zig/system/linux.zig
index ac68791a16..bbe7f8eaf9 100644
--- a/lib/std/zig/system/linux.zig
+++ b/lib/std/zig/system/linux.zig
@@ -359,14 +359,11 @@ fn CpuinfoParser(comptime impl: anytype) type {
     return struct {
         fn parse(arch: Target.Cpu.Arch, reader: *std.Io.Reader) !?Target.Cpu {
             var obj: impl = .{};
-            while (reader.takeDelimiterExclusive('\n')) |line| {
+            while (try reader.takeDelimiter('\n')) |line| {
                 const colon_pos = mem.indexOfScalar(u8, line, ':') orelse continue;
                 const key = mem.trimEnd(u8, line[0..colon_pos], " \t");
                 const value = mem.trimStart(u8, line[colon_pos + 1 ..], " \t");
                 if (!try obj.line_hook(key, value)) break;
-            } else |err| switch (err) {
-                error.EndOfStream => {},
-                else => |e| return e,
             }
             return obj.finalize(arch);
         }
diff --git a/src/link/MappedFile.zig b/src/link/MappedFile.zig
index c44f1f68fb..fd182a353d 100644
--- a/src/link/MappedFile.zig
+++ b/src/link/MappedFile.zig
@@ -411,7 +411,8 @@ pub const Node = extern struct {
                 .failure,
                 => {
                     const dest = limit.slice(interface.unusedCapacitySlice());
-                    const n = try file_reader.read(dest);
+                    const n = try file_reader.interface.readSliceShort(dest);
+                    if (n == 0) return error.EndOfStream;
                     interface.end += n;
                     return n;
                 },
diff --git a/test/tests.zig b/test/tests.zig
index fb449d5bf4..67f410019f 100644
--- a/test/tests.zig
+++ b/test/tests.zig
@@ -44,7 +44,7 @@ const test_targets = blk: {
     break :blk [_]TestTarget{
         // Native Targets
 
-        .{},
+        .{}, // 0 index must be all defaults
         .{
             .link_libc = true,
         },
@@ -2224,6 +2224,7 @@ const ModuleTestOptions = struct {
     desc: []const u8,
     optimize_modes: []const OptimizeMode,
     include_paths: []const []const u8,
+    test_default_only: bool,
     skip_single_threaded: bool,
     skip_non_native: bool,
     skip_freebsd: bool,
@@ -2235,13 +2236,21 @@ const ModuleTestOptions = struct {
     skip_libc: bool,
     max_rss: usize = 0,
     no_builtin: bool = false,
-    build_options: ?*std.Build.Step.Options = null,
+    build_options: ?*Step.Options = null,
 };
 
 pub fn addModuleTests(b: *std.Build, options: ModuleTestOptions) *Step {
     const step = b.step(b.fmt("test-{s}", .{options.name}), options.desc);
 
-    for_targets: for (test_targets) |test_target| {
+    if (options.test_default_only) {
+        const test_target = &test_targets[0];
+        const resolved_target = b.resolveTargetQuery(test_target.target);
+        const triple_txt = resolved_target.query.zigTriple(b.allocator) catch @panic("OOM");
+        addOneModuleTest(b, step, test_target, &resolved_target, triple_txt, options);
+        return step;
+    }
+
+    for_targets: for (&test_targets) |*test_target| {
         if (test_target.skip_modules.len > 0) {
             for (test_target.skip_modules) |skip_mod| {
                 if (std.mem.eql(u8, options.name, skip_mod)) continue :for_targets;
@@ -2306,169 +2315,182 @@ pub fn addModuleTests(b: *std.Build, options: ModuleTestOptions) *Step {
         } else false;
         if (!want_this_mode) continue;
 
-        const libc_suffix = if (test_target.link_libc == true) "-libc" else "";
-        const model_txt = target.cpu.model.name;
-
-        // wasm32-wasi builds need more RAM, idk why
-        const max_rss = if (target.os.tag == .wasi)
-            options.max_rss * 2
-        else
-            options.max_rss;
-
-        const these_tests = b.addTest(.{
-            .root_module = b.createModule(.{
-                .root_source_file = b.path(options.root_src),
-                .optimize = test_target.optimize_mode,
-                .target = resolved_target,
-                .link_libc = test_target.link_libc,
-                .pic = test_target.pic,
-                .strip = test_target.strip,
-                .single_threaded = test_target.single_threaded,
-            }),
-            .max_rss = max_rss,
-            .filters = options.test_filters,
-            .use_llvm = test_target.use_llvm,
-            .use_lld = test_target.use_lld,
-            .zig_lib_dir = b.path("lib"),
-        });
-        these_tests.linkage = test_target.linkage;
-        if (options.no_builtin) these_tests.root_module.no_builtin = false;
-        if (options.build_options) |build_options| {
-            these_tests.root_module.addOptions("build_options", build_options);
-        }
-        const single_threaded_suffix = if (test_target.single_threaded == true) "-single" else "";
-        const backend_suffix = if (test_target.use_llvm == true)
-            "-llvm"
-        else if (target.ofmt == std.Target.ObjectFormat.c)
-            "-cbe"
-        else if (test_target.use_llvm == false)
-            "-selfhosted"
-        else
-            "";
-        const use_lld = if (test_target.use_lld == false) "-no-lld" else "";
-        const linkage_name = if (test_target.linkage) |linkage| switch (linkage) {
-            inline else => |t| "-" ++ @tagName(t),
-        } else "";
-        const use_pic = if (test_target.pic == true) "-pic" else "";
-
-        for (options.include_paths) |include_path| these_tests.root_module.addIncludePath(b.path(include_path));
-
-        const qualified_name = b.fmt("{s}-{s}-{s}-{s}{s}{s}{s}{s}{s}{s}", .{
-            options.name,
-            triple_txt,
-            model_txt,
-            @tagName(test_target.optimize_mode),
-            libc_suffix,
-            single_threaded_suffix,
-            backend_suffix,
-            use_lld,
-            linkage_name,
-            use_pic,
-        });
-
-        if (target.ofmt == std.Target.ObjectFormat.c) {
-            var altered_query = test_target.target;
-            altered_query.ofmt = null;
-
-            const compile_c = b.createModule(.{
-                .root_source_file = null,
-                .link_libc = test_target.link_libc,
-                .target = b.resolveTargetQuery(altered_query),
-            });
-            const compile_c_exe = b.addExecutable(.{
-                .name = qualified_name,
-                .root_module = compile_c,
-                .zig_lib_dir = b.path("lib"),
-            });
-
-            compile_c.addCSourceFile(.{
-                .file = these_tests.getEmittedBin(),
-                .flags = &.{
-                    // Tracking issue for making the C backend generate C89 compatible code:
-                    // https://github.com/ziglang/zig/issues/19468
-                    "-std=c99",
-                    "-Werror",
-
-                    "-Wall",
-                    "-Wembedded-directive",
-                    "-Wempty-translation-unit",
-                    "-Wextra",
-                    "-Wgnu",
-                    "-Winvalid-utf8",
-                    "-Wkeyword-macro",
-                    "-Woverlength-strings",
-
-                    // Tracking issue for making the C backend generate code
-                    // that does not trigger warnings:
-                    // https://github.com/ziglang/zig/issues/19467
-
-                    // spotted everywhere
-                    "-Wno-builtin-requires-header",
-
-                    // spotted on linux
-                    "-Wno-braced-scalar-init",
-                    "-Wno-excess-initializers",
-                    "-Wno-incompatible-pointer-types-discards-qualifiers",
-                    "-Wno-unused",
-                    "-Wno-unused-parameter",
-
-                    // spotted on darwin
-                    "-Wno-incompatible-pointer-types",
-
-                    // https://github.com/llvm/llvm-project/issues/153314
-                    "-Wno-unterminated-string-initialization",
-
-                    // In both Zig and C it is legal to return a pointer to a
-                    // local. The C backend lowers such thing directly, so the
-                    // corresponding warning in C must be disabled.
-                    "-Wno-return-stack-address",
-                },
-            });
-            compile_c.addIncludePath(b.path("lib")); // for zig.h
-            if (target.os.tag == .windows) {
-                if (true) {
-                    // Unfortunately this requires about 8G of RAM for clang to compile
-                    // and our Windows CI runners do not have this much.
-                    step.dependOn(&these_tests.step);
-                    continue;
-                }
-                if (test_target.link_libc == false) {
-                    compile_c_exe.subsystem = .Console;
-                    compile_c.linkSystemLibrary("kernel32", .{});
-                    compile_c.linkSystemLibrary("ntdll", .{});
-                }
-                if (mem.eql(u8, options.name, "std")) {
-                    if (test_target.link_libc == false) {
-                        compile_c.linkSystemLibrary("shell32", .{});
-                        compile_c.linkSystemLibrary("advapi32", .{});
-                    }
-                    compile_c.linkSystemLibrary("crypt32", .{});
-                    compile_c.linkSystemLibrary("ws2_32", .{});
-                    compile_c.linkSystemLibrary("ole32", .{});
-                }
-            }
-
-            const run = b.addRunArtifact(compile_c_exe);
-            run.skip_foreign_checks = true;
-            run.enableTestRunnerMode();
-            run.setName(b.fmt("run test {s}", .{qualified_name}));
-
-            step.dependOn(&run.step);
-        } else if (target.cpu.arch.isSpirV()) {
-            // Don't run spirv binaries
-            _ = these_tests.getEmittedBin();
-            step.dependOn(&these_tests.step);
-        } else {
-            const run = b.addRunArtifact(these_tests);
-            run.skip_foreign_checks = true;
-            run.setName(b.fmt("run test {s}", .{qualified_name}));
-
-            step.dependOn(&run.step);
-        }
+        addOneModuleTest(b, step, test_target, &resolved_target, triple_txt, options);
     }
     return step;
 }
 
+fn addOneModuleTest(
+    b: *std.Build,
+    step: *Step,
+    test_target: *const TestTarget,
+    resolved_target: *const std.Build.ResolvedTarget,
+    triple_txt: []const u8,
+    options: ModuleTestOptions,
+) void {
+    const target = &resolved_target.result;
+    const libc_suffix = if (test_target.link_libc == true) "-libc" else "";
+    const model_txt = target.cpu.model.name;
+
+    // wasm32-wasi builds need more RAM, idk why
+    const max_rss = if (target.os.tag == .wasi)
+        options.max_rss * 2
+    else
+        options.max_rss;
+
+    const these_tests = b.addTest(.{
+        .root_module = b.createModule(.{
+            .root_source_file = b.path(options.root_src),
+            .optimize = test_target.optimize_mode,
+            .target = resolved_target.*,
+            .link_libc = test_target.link_libc,
+            .pic = test_target.pic,
+            .strip = test_target.strip,
+            .single_threaded = test_target.single_threaded,
+        }),
+        .max_rss = max_rss,
+        .filters = options.test_filters,
+        .use_llvm = test_target.use_llvm,
+        .use_lld = test_target.use_lld,
+        .zig_lib_dir = b.path("lib"),
+    });
+    these_tests.linkage = test_target.linkage;
+    if (options.no_builtin) these_tests.root_module.no_builtin = false;
+    if (options.build_options) |build_options| {
+        these_tests.root_module.addOptions("build_options", build_options);
+    }
+    const single_threaded_suffix = if (test_target.single_threaded == true) "-single" else "";
+    const backend_suffix = if (test_target.use_llvm == true)
+        "-llvm"
+    else if (target.ofmt == std.Target.ObjectFormat.c)
+        "-cbe"
+    else if (test_target.use_llvm == false)
+        "-selfhosted"
+    else
+        "";
+    const use_lld = if (test_target.use_lld == false) "-no-lld" else "";
+    const linkage_name = if (test_target.linkage) |linkage| switch (linkage) {
+        inline else => |t| "-" ++ @tagName(t),
+    } else "";
+    const use_pic = if (test_target.pic == true) "-pic" else "";
+
+    for (options.include_paths) |include_path| these_tests.root_module.addIncludePath(b.path(include_path));
+
+    const qualified_name = b.fmt("{s}-{s}-{s}-{t}{s}{s}{s}{s}{s}{s}", .{
+        options.name,
+        triple_txt,
+        model_txt,
+        test_target.optimize_mode,
+        libc_suffix,
+        single_threaded_suffix,
+        backend_suffix,
+        use_lld,
+        linkage_name,
+        use_pic,
+    });
+
+    if (target.ofmt == std.Target.ObjectFormat.c) {
+        var altered_query = test_target.target;
+        altered_query.ofmt = null;
+
+        const compile_c = b.createModule(.{
+            .root_source_file = null,
+            .link_libc = test_target.link_libc,
+            .target = b.resolveTargetQuery(altered_query),
+        });
+        const compile_c_exe = b.addExecutable(.{
+            .name = qualified_name,
+            .root_module = compile_c,
+            .zig_lib_dir = b.path("lib"),
+        });
+
+        compile_c.addCSourceFile(.{
+            .file = these_tests.getEmittedBin(),
+            .flags = &.{
+                // Tracking issue for making the C backend generate C89 compatible code:
+                // https://github.com/ziglang/zig/issues/19468
+                "-std=c99",
+                "-Werror",
+
+                "-Wall",
+                "-Wembedded-directive",
+                "-Wempty-translation-unit",
+                "-Wextra",
+                "-Wgnu",
+                "-Winvalid-utf8",
+                "-Wkeyword-macro",
+                "-Woverlength-strings",
+
+                // Tracking issue for making the C backend generate code
+                // that does not trigger warnings:
+                // https://github.com/ziglang/zig/issues/19467
+
+                // spotted everywhere
+                "-Wno-builtin-requires-header",
+
+                // spotted on linux
+                "-Wno-braced-scalar-init",
+                "-Wno-excess-initializers",
+                "-Wno-incompatible-pointer-types-discards-qualifiers",
+                "-Wno-unused",
+                "-Wno-unused-parameter",
+
+                // spotted on darwin
+                "-Wno-incompatible-pointer-types",
+
+                // https://github.com/llvm/llvm-project/issues/153314
+                "-Wno-unterminated-string-initialization",
+
+                // In both Zig and C it is legal to return a pointer to a
+                // local. The C backend lowers such thing directly, so the
+                // corresponding warning in C must be disabled.
+                "-Wno-return-stack-address",
+            },
+        });
+        compile_c.addIncludePath(b.path("lib")); // for zig.h
+        if (target.os.tag == .windows) {
+            if (true) {
+                // Unfortunately this requires about 8G of RAM for clang to compile
+                // and our Windows CI runners do not have this much.
+                // TODO This is not an appropriate way to work around this problem.
+                step.dependOn(&these_tests.step);
+                return;
+            }
+            if (test_target.link_libc == false) {
+                compile_c_exe.subsystem = .Console;
+                compile_c.linkSystemLibrary("kernel32", .{});
+                compile_c.linkSystemLibrary("ntdll", .{});
+            }
+            if (mem.eql(u8, options.name, "std")) {
+                if (test_target.link_libc == false) {
+                    compile_c.linkSystemLibrary("shell32", .{});
+                    compile_c.linkSystemLibrary("advapi32", .{});
+                }
+                compile_c.linkSystemLibrary("crypt32", .{});
+                compile_c.linkSystemLibrary("ws2_32", .{});
+                compile_c.linkSystemLibrary("ole32", .{});
+            }
+        }
+
+        const run = b.addRunArtifact(compile_c_exe);
+        run.skip_foreign_checks = true;
+        run.enableTestRunnerMode();
+        run.setName(b.fmt("run test {s}", .{qualified_name}));
+
+        step.dependOn(&run.step);
+    } else if (target.cpu.arch.isSpirV()) {
+        // Don't run spirv binaries
+        _ = these_tests.getEmittedBin();
+        step.dependOn(&these_tests.step);
+    } else {
+        const run = b.addRunArtifact(these_tests);
+        run.skip_foreign_checks = true;
+        run.setName(b.fmt("run test {s}", .{qualified_name}));
+
+        step.dependOn(&run.step);
+    }
+}
+
 pub fn wouldUseLlvm(use_llvm: ?bool, query: std.Target.Query, optimize_mode: OptimizeMode) bool {
     if (use_llvm) |x| return x;
     if (query.ofmt == .c) return false;