[gcc(refs/vendors/ARM/heads/gcs-13)] libgcc: aarch64: Add SME unwinder support

[gcc(refs/vendors/ARM/heads/gcs-13)] libgcc: aarch64: Add SME unwinder support

[Szabolcs Nagy]

https://gcc.gnu.org/g:b33d3beaf89a1853e304c3c023d49fb130c4fa33

commit b33d3beaf89a1853e304c3c023d49fb130c4fa33
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Fri Sep 29 13:55:51 2023 +0100

    libgcc: aarch64: Add SME unwinder support
    
    To support the ZA lazy save scheme, the PCS requires the unwinder to
    reset the SME state to PSTATE.SM=0, PSTATE.ZA=0, TPIDR2_EL0=0 on entry
    to an exception handler. We use the __arm_za_disable SME runtime call
    unconditionally to achieve this.
    https://github.com/ARM-software/abi-aa/blob/main/aapcs64/aapcs64.rst#exceptions
    
    The hidden alias is used to avoid a PLT and avoid inconsistent VPCS
    marking (we don't rely on special PCS at the call site). In case of
    static linking the SME runtime init code is linked in code that raises
    exceptions.
    
    libgcc/ChangeLog:
    
            * config/aarch64/__arm_za_disable.S: Add hidden alias.
            * config/aarch64/aarch64-unwind.h: Reset the SME state before
            EH return via the _Unwind_Frames_Extra hook.
    
    (cherry picked from commit 91d68665b8b7a5dffd0bbf8cd1f74c3c41d4c2d8)

Diff:
---
 libgcc/config/aarch64/__arm_za_disable.S |  5 +++++
 libgcc/config/aarch64/aarch64-unwind.h   | 16 ++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/libgcc/config/aarch64/__arm_za_disable.S b/libgcc/config/aarch64/__arm_za_disable.S
index cff5b9cec47e..03fc28a39317 100644
--- a/libgcc/config/aarch64/__arm_za_disable.S
+++ b/libgcc/config/aarch64/__arm_za_disable.S
@@ -63,3 +63,8 @@ ENTRY (__arm_za_disable)
 L(end):
 	ret
 END (__arm_za_disable)
+
+/* Hidden alias used by the unwinder.  */
+.global __libgcc_arm_za_disable
+.hidden __libgcc_arm_za_disable
+.set __libgcc_arm_za_disable, __arm_za_disable
diff --git a/libgcc/config/aarch64/aarch64-unwind.h b/libgcc/config/aarch64/aarch64-unwind.h
index 3ad2f8239ed8..df223d8f6bb3 100644
--- a/libgcc/config/aarch64/aarch64-unwind.h
+++ b/libgcc/config/aarch64/aarch64-unwind.h
@@ -77,4 +77,20 @@ aarch64_demangle_return_addr (struct _Unwind_Context *context,
   return addr;
 }
 
+/* SME runtime function local to libgcc, streaming compatible
+   and preserves more registers than the base PCS requires, but
+   we don't rely on that here.  */
+__attribute__ ((visibility ("hidden")))
+void __libgcc_arm_za_disable (void);
+
+/* Disable the SME ZA state in case an unwound frame used the ZA
+   lazy saving scheme.  */
+#undef _Unwind_Frames_Extra
+#define _Unwind_Frames_Extra(x)				\
+  do							\
+    {							\
+      __libgcc_arm_za_disable ();			\
+    }							\
+  while (0)
+
 #endif /* defined AARCH64_UNWIND_H && defined __ILP32__ */