runtime: fallback to TEB arbitrary pointer when TLS slots are full

The Go runtime allocates the TLS slot in the TEB TLS slots instead of
using the TEB arbitrary pointer. See CL 431775 for more context.

The problem is that the TEB TLS slots array only has capacity for 64
indices, allocating more requires some complex logic that we don't
support yet.

Although the Go runtime only allocates one index, a Go DLL can be
loaded in a process with more than 64 TLS slots allocated,
in which case it abort.

This CL avoids aborting by falling back to the older behavior, that
is to use the TEB arbitrary pointer.

Fixes #59213

Change-Id: I39c73286fe2da95aa9c5ec5657ee0979ecbec533
Reviewed-on: https://go-review.googlesource.com/c/go/+/486816
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

2 files changed, 41 insertions, 0 deletions

diff --git a/src/runtime/testdata/testwintls/main.c b/src/runtime/testdata/testwintls/main.c
new file mode 100644
index 0000000000..606182859c
--- /dev/null
+++ b/src/runtime/testdata/testwintls/main.c
@@ -0,0 +1,29 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+#include <windows.h>
+
+int main(int argc, char **argv) {
+    if (argc < 3) {
+        return 1;
+    }
+    // Allocate more than 64 TLS indices
+    // so the Go runtime doesn't find
+    // enough space in the TEB TLS slots.
+    for (int i = 0; i < 65; i++) {
+        TlsAlloc();
+    }
+    HMODULE hlib = LoadLibrary(argv[1]);
+    if (hlib == NULL) {
+        return 2;
+    }
+    FARPROC proc = GetProcAddress(hlib, argv[2]);
+    if (proc == NULL) {
+        return 3;
+    }
+    if (proc() != 42) {
+        return 4;
+    }
+    return 0;
+}
\ No newline at end of file
diff --git a/src/runtime/testdata/testwintls/main.go b/src/runtime/testdata/testwintls/main.go
new file mode 100644
index 0000000000..1cf296c403
--- /dev/null
+++ b/src/runtime/testdata/testwintls/main.go
@@ -0,0 +1,12 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "C"
+
+//export GoFunc
+func GoFunc() int { return 42 }
+
+func main() {}