[PATCH] Cygwin: malloc_wrapper: port to AArch64

[Radek Barton]

Hello.

This patch implements `import_address` function by decoding `adr` AArch64 instructions to get
target address.

Radek

---
From 8bfc01898261e341bbc8abb437e159b6b33a9312 Mon Sep 17 00:00:00 2001
From: Evgeny Karpov <evgeny.karpov@microsoft.com>
Date: Fri, 4 Jul 2025 20:20:37 +0200
Subject: [PATCH] Cygwin: malloc_wrapper: port to AArch64
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Implements import_address function by decoding adr AArch64 instructions to get
target address.

Signed-off-by: Evgeny Karpov <evgeny.karpov@microsoft.com>
---
 winsup/cygwin/mm/malloc_wrapper.cc | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/winsup/cygwin/mm/malloc_wrapper.cc b/winsup/cygwin/mm/malloc_wrapper.cc
index de3cf7ddc..863d3089c 100644
--- a/winsup/cygwin/mm/malloc_wrapper.cc
+++ b/winsup/cygwin/mm/malloc_wrapper.cc
@@ -50,6 +50,19 @@ import_address (void *imp)
 {
   __try
     {
+#if defined(__aarch64__)
+      // If opcode is an adr instruction.
+      uint32_t opcode = *(uint32_t *) imp;
+      if ((opcode & 0x9f000000) == 0x10000000)
+     {
+       uint32_t immhi = (opcode >> 5) & 0x7ffff;
+       uint32_t immlo = (opcode >> 29) & 0x3;
+       int64_t sign_extend = (0l - (immhi >> 18)) << 21;
+       int64_t imm = sign_extend | (immhi << 2) | immlo;
+       uintptr_t jmpto = *(uintptr_t *) ((uint8_t *) imp + imm);
+       return (void *) jmpto;
+     }
+#else
       if (*((uint16_t *) imp) == 0x25ff)
      {
        const char *ptr = (const char *) imp;
@@ -57,6 +70,7 @@ import_address (void *imp)
                           (ptr + 6 + *(int32_t *)(ptr + 2));
        return (void *) *jmpto;
      }
+#endif
     }
   __except (NO_ERROR) {}
   __endtry
--
2.50.1.vfs.0.0

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