[gcc r15-3801] aarch64: skip copy of RA state register into target context

[Tamar Christina]

https://gcc.gnu.org/g:ba3e597681b640f6f9a676ec4f6cd3ca3878cefc

commit r15-3801-gba3e597681b640f6f9a676ec4f6cd3ca3878cefc
Author: Matthieu Longo <matthieu.longo@arm.com>
Date:   Mon Sep 23 15:03:35 2024 +0100

    aarch64: skip copy of RA state register into target context
    
    The RA state register is local to a frame, so it should not be copied to
    the target frame during the context installation.
    
    This patch adds a new backend handler that check whether a register
    needs to be skipped or not before its installation.
    
    libgcc/ChangeLog:
    
            * config/aarch64/aarch64-unwind.h
            (MD_FRAME_LOCAL_REGISTER_P): new handler checking whether a register
            from the current context needs to be skipped before installation into
            the target context.
            (aarch64_frame_local_register): Likewise.
            * unwind-dw2.c (uw_install_context_1): use MD_FRAME_LOCAL_REGISTER_P.

Diff:
---
 libgcc/config/aarch64/aarch64-unwind.h | 11 +++++++++++
 libgcc/unwind-dw2.c                    |  5 +++++
 2 files changed, 16 insertions(+)

diff --git a/libgcc/config/aarch64/aarch64-unwind.h b/libgcc/config/aarch64/aarch64-unwind.h
index 94ea5891b4eb..52bfd5409798 100644
--- a/libgcc/config/aarch64/aarch64-unwind.h
+++ b/libgcc/config/aarch64/aarch64-unwind.h
@@ -53,6 +53,9 @@ typedef enum {
 #define MD_DEMANGLE_RETURN_ADDR(context, fs, addr) \
   aarch64_demangle_return_addr (context, fs, addr)
 
+#define MD_FRAME_LOCAL_REGISTER_P(reg) \
+  aarch64_frame_local_register (reg)
+
 static inline aarch64_ra_signing_method_t
 aarch64_context_ra_state_get (struct _Unwind_Context *context)
 {
@@ -127,6 +130,14 @@ aarch64_arch_extension_frame_init (struct _Unwind_Context *context ATTRIBUTE_UNU
   aarch64_fs_ra_state_set (fs, aarch64_ra_no_signing);
 }
 
+/* Before copying the current context to the target context, check whether
+   the register is local to this context and should not be forwarded.  */
+static inline bool
+aarch64_frame_local_register(long reg)
+{
+  return (reg == AARCH64_DWARF_REGNUM_RA_STATE);
+}
+
 /* Do AArch64 private extraction on ADDR_WORD based on context info CONTEXT and
    unwind frame info FS.  If ADDR_WORD is signed, we do address authentication
    on it using CFA of current frame.
diff --git a/libgcc/unwind-dw2.c b/libgcc/unwind-dw2.c
index 40d64c0c0a39..5f33f80670ac 100644
--- a/libgcc/unwind-dw2.c
+++ b/libgcc/unwind-dw2.c
@@ -1423,6 +1423,11 @@ uw_install_context_1 (struct _Unwind_Context *current,
       void *c = (void *) (_Unwind_Internal_Ptr) current->reg[i];
       void *t = (void *) (_Unwind_Internal_Ptr)target->reg[i];
 
+#ifdef MD_FRAME_LOCAL_REGISTER_P
+      if (MD_FRAME_LOCAL_REGISTER_P (i))
+	continue;
+#endif
+
       gcc_assert (current->by_value[i] == 0);
       if (target->by_value[i] && c)
 	{