runtime,cmd/internal/obj/x86: use TEB TLS slots on windows/amd64

This CL redesign how we get the TLS pointer on windows/amd64.

We were previously reading it from the [TEB] arbitrary data slot,
located at 0x28(GS), which can only hold 1 TLS pointer.

With this CL, we will read the TLS pointer from the TEB TLS slot array,
located at 0x1480(GS). The TLS slot array can hold multiple
TLS pointers, up to 64, so multiple Go runtimes running on the
same thread can coexists with different TLS.

Each new TLS slot has to be allocated via [TlsAlloc],
which returns the slot index. This index can then be used to get the
slot offset from GS with the following formula: 0x1480 + index*8

The slot index is fixed per Go runtime, so we can store it
in runtime.tls_g and use it latter on to read/update the TLS pointer.

Loading the TLS pointer requires the following asm instructions:

  MOVQ runtime.tls_g, AX
  MOVQ AX(GS), AX

Notice that this approach is also implemented on windows/arm64.

[TEB]: https://en.wikipedia.org/wiki/Win32_Thread_Information_Block
[TlsAlloc]: https://learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-tlsalloc

Updates #22192

Change-Id: Idea7119fd76a3cd083979a4d57ed64b552fa101b
Reviewed-on: https://go-review.googlesource.com/c/go/+/431775
Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/runtime/cgo/gcc_windows_amd64.c b/src/runtime/cgo/gcc_windows_amd64.c
index 996947eccf..3ff3c64565 100644
--- a/src/runtime/cgo/gcc_windows_amd64.c
+++ b/src/runtime/cgo/gcc_windows_amd64.c
@@ -13,11 +13,13 @@
 
 static void threadentry(void*);
 static void (*setg_gcc)(void*);
+static DWORD *tls_g;
 
 void
 x_cgo_init(G *g, void (*setg)(void*), void **tlsg, void **tlsbase)
 {
 	setg_gcc = setg;
+	tls_g = (DWORD *)tlsg;
 }
 
 
@@ -41,8 +43,8 @@ threadentry(void *v)
 	 * Set specific keys in thread local storage.
 	 */
 	asm volatile (
-	  "movq %0, %%gs:0x28\n"	// MOVL tls0, 0x28(GS)
-	  :: "r"(ts.tls)
+	  "movq %0, %%gs:0(%1)\n"	// MOVL tls0, 0(tls_g)(GS)
+	  :: "r"(ts.tls), "r"(*tls_g)
 	);
 
 	crosscall_amd64(ts.fn, setg_gcc, (void*)ts.g);