[PATCH] Cygwin: obtain stack base on AArch64

[Radek Barton via Cygwin-patches]

Hello.

This patch ports reading of stack base from TEB on AArch64 at cygload.cc and 
__getreent.

Radek

---
>From 08f9be50573a085fd3e5cb840455ea5fc3b1e82a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Radek=20Barto=C5=88?= <radek.bar...@microsoft.com>
Date: Wed, 4 Jun 2025 13:38:10 +0200
Subject: [PATCH] Cygwin: obtain stack base on AArch64
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Content-Type: text/plain; charset=UTF-8
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Signed-off-by: Radek Bartoň <radek.bar...@microsoft.com>
---
 winsup/cygwin/include/cygwin/config.h  | 7 ++++++-
 winsup/testsuite/winsup.api/cygload.cc | 7 +++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/include/cygwin/config.h 
b/winsup/cygwin/include/cygwin/config.h
index 2a7083278..d9f911d47 100644
--- a/winsup/cygwin/include/cygwin/config.h
+++ b/winsup/cygwin/include/cygwin/config.h
@@ -36,8 +36,13 @@ __attribute__((__gnu_inline__))
 extern inline struct _reent *__getreent (void)
 {
   register char *ret;
-#ifdef __x86_64__
+#if defined(__x86_64__)
   __asm __volatile__ ("movq %%gs:8,%0" : "=r" (ret));
+#elif defined(__aarch64__)
+  /* x18 register points to TEB, offset 0x8 points to stack base.
+     See _TEB structure definition in winsup\cygwin\local_includes\ntdll.h
+     for more details. */
+  __asm __volatile__ ("ldr %0, [x18, #0x8]" : "=r" (ret));
 #else
 #error unimplemented for this target
 #endif
diff --git a/winsup/testsuite/winsup.api/cygload.cc 
b/winsup/testsuite/winsup.api/cygload.cc
index afd3ee90f..08372a302 100644
--- a/winsup/testsuite/winsup.api/cygload.cc
+++ b/winsup/testsuite/winsup.api/cygload.cc
@@ -82,6 +82,13 @@ cygwin::padding::padding ()
     "movl %%fs:4, %0"
     :"=r"(stackbase)
     );
+# elif __aarch64__
+  // x18 register points to TEB. See _TEB structure definition in
+  // winsup\cygwin\local_includes\ntdll.h
+  __asm__ volatile (
+    "ldr %0, [x18, #0x8]"
+   :"=r" (stackbase)
+   );
 # else
 #  error Unknown architecture
 # endif
-- 
2.49.0.vfs.0.4

0001-Cygwin-obtain-stack-base-on-AArch64.patch
Description: 0001-Cygwin-obtain-stack-base-on-AArch64.patch