[libunwind] [libunwind] Fix an uninitialized read of __ra_sign_state (PR #205152)

[Jon Roelofs via cfe-commits]

https://github.com/jroelofs created https://github.com/llvm/llvm-project/pull/205152

The Arm DWARF spec defines UNW_AARCH64_RA_SIGN_STATE as being zeroed until the first .cfi_negate_ra_state / .cfi_set_ra_state [1]. The GPRs struct containing __ra_sign_state is memcpy'd directly from the unw_context_t, which in turn is initialized by __unw_getcontext. Since it is a pseudo register, there is no corresponding state to restore in __unw_resume.

https://github.com/ARM-software/abi-aa/blob/main/aadwarf64/aadwarf64.rst#44call-frame-instructions

>From 643822ea84f6347d9b662ff4f0cf2bef97da041a Mon Sep 17 00:00:00 2001
From: Jon Roelofs <jonathan_roelofs at apple.com>
Date: Thu, 18 Jun 2026 17:44:35 -0700
Subject: [PATCH] [libunwind] Fix an uninitialized read of __ra_sign_state

The Arm DWARF spec defines UNW_AARCH64_RA_SIGN_STATE as being zeroed until the
first .cfi_negate_ra_state / .cfi_set_ra_state [1]. The GPRs struct containing
__ra_sign_state is memcpy'd directly from the unw_context_t, which in turn is
initialized by __unw_getcontext. Since it is a pseudo register, there is no
corresponding state to restore in __unw_resume.

https://github.com/ARM-software/abi-aa/blob/main/aadwarf64/aadwarf64.rst#44call-frame-instructions
---
 libunwind/src/UnwindRegistersSave.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/libunwind/src/UnwindRegistersSave.S b/libunwind/src/UnwindRegistersSave.S
index ca9a97b18e764..a82ebd1ead23b 100644
--- a/libunwind/src/UnwindRegistersSave.S
+++ b/libunwind/src/UnwindRegistersSave.S
@@ -807,6 +807,7 @@ DEFINE_LIBUNWIND_FUNCTION(__unw_getcontext)
   mov    x1,sp
   str    x1,      [x0, #0x0F8]
   str    x30,     [x0, #0x100]    // store return address as pc
+  str    xzr,     [x0, #0x108]    // zero __ra_sign_state
   // skip cpsr
 #if defined(__ARM_FP) && __ARM_FP != 0
   stp    d0, d1,  [x0, #0x110]