[PATCH v5 02/13] aarch64: Implement gdbarch function top_addr_empty_shadow_stack.

[Christina Joos <christina.joos@intel.com>]

From: Thiago Jung Bauermann <thiago.bauermann@linaro.org>

With the implementation of that gdbarch function we can remove
the arch specific function aarch64_linux_dwarf2_prev_gcspr and
use the generalized function dwarf2_prev_ssp instead.

Co-Authored-By: Christina Joos <christina.joos@intel.com>
---
 gdb/aarch64-linux-tdep.c | 51 ++--------------------------------------
 gdb/aarch64-tdep.c       | 31 ++++++++++++++++++++++--
 2 files changed, 31 insertions(+), 51 deletions(-)

diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
index 235b35bcfb4..57e3c304469 100644
--- a/gdb/aarch64-linux-tdep.c
+++ b/gdb/aarch64-linux-tdep.c
@@ -66,6 +66,7 @@
 #include "elf/common.h"
 #include "elf/aarch64.h"
 #include "arch/aarch64-insn.h"
+#include "shadow-stack.h"
 
 /* For std::pow */
 #include <cmath>
@@ -2617,54 +2618,6 @@ aarch64_linux_get_shadow_stack_pointer (gdbarch *gdbarch, regcache *regcache,
   return gcspr;
 }
 
-/* Implement Guarded Control Stack Pointer Register unwinding.  For each
-   previous GCS pointer check if its address is still in the GCS memory
-   range.  If it's outside the range set the returned value to unavailable,
-   otherwise return a value containing the new GCS pointer.  */
-
-static value *
-aarch64_linux_dwarf2_prev_gcspr (const frame_info_ptr &this_frame,
-				 void **this_cache, int regnum)
-{
-  value *v = frame_unwind_got_register (this_frame, regnum, regnum);
-  gdb_assert (v != nullptr);
-
-  gdbarch *gdbarch = get_frame_arch (this_frame);
-
-  if (v->entirely_available () && !v->optimized_out ())
-    {
-      int size = register_size (gdbarch, regnum);
-      bfd_endian byte_order = gdbarch_byte_order (gdbarch);
-      CORE_ADDR gcspr = extract_unsigned_integer (v->contents_all ().data (),
-						  size, byte_order);
-
-      /* Starting with v6.13, the Linux kernel supports Guarded Control
-	 Stack.  Using /proc/PID/smaps we can only check if the current
-	 GCSPR points to GCS memory.  Only if this is the case a valid
-	 previous GCS pointer can be calculated.  */
-      std::pair<CORE_ADDR, CORE_ADDR> range;
-      if (linux_address_in_shadow_stack_mem_range (gcspr, &range))
-	{
-	  /* The GCS grows downwards.  To compute the previous GCS pointer,
-	     we need to increment the GCSPR.  */
-	  CORE_ADDR new_gcspr = gcspr + 8;
-
-	  /* If NEW_GCSPR still points within the current GCS memory range
-	     we consider it to be valid.  */
-	  if (new_gcspr < range.second)
-	    return frame_unwind_got_address (this_frame, regnum, new_gcspr);
-	}
-    }
-
-  /* Return a value which is marked as unavailable in case we could not
-     calculate a valid previous GCS pointer.  */
-  value *retval
-    = value::allocate_register (get_next_frame_sentinel_okay (this_frame),
-				regnum, register_type (gdbarch, regnum));
-  retval->mark_bytes_unavailable (0, retval->type ()->length ());
-  return retval;
-}
-
 /* AArch64 Linux implementation of the report_signal_info gdbarch
    hook.  Displays information about possible memory tag violations.  */
 
@@ -3245,7 +3198,7 @@ aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
     {
       set_gdbarch_get_shadow_stack_pointer (gdbarch,
 					aarch64_linux_get_shadow_stack_pointer);
-      tdep->fn_prev_gcspr = aarch64_linux_dwarf2_prev_gcspr;
+      tdep->fn_prev_gcspr = dwarf2_prev_ssp;
     }
 }
 
diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index 848cee3043c..94893dd4bcf 100644
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -1908,6 +1908,26 @@ aarch64_pop_gcs_entry (regcache *regs)
   regcache_cooked_write_unsigned (regs, tdep->gcs_reg_base, gcs_addr + 8);
 }
 
+/* Implement the "top_addr_empty_shadow_stack" gdbarch method.  */
+
+static bool
+aarch64_top_addr_empty_shadow_stack
+  (const CORE_ADDR addr,
+   const std::pair<CORE_ADDR, CORE_ADDR> range)
+{
+  gdb_assert (addr >= range.first);
+
+  /* For AArch64, addr must be strictly less than the upper address in the
+     range, but other architectures allow it to be equal to the upper
+     address when the stack is empty so GDB core works with those addresses
+     and can send them our way.  */
+  gdb_assert (addr <= range.second);
+
+  /* The GCS grows down, and the oldest entry is the value '0', not an
+     address.  */
+  return addr >= range.second - 8;
+}
+
 /* Implement the "push_dummy_call" gdbarch method.  */
 
 static CORE_ADDR
@@ -4783,9 +4803,16 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   /* Register a hook for converting a memory tag to a string.  */
   set_gdbarch_memtag_to_string (gdbarch, aarch64_memtag_to_string);
 
-  /* AArch64's shadow stack pointer is the GCSPR.  */
   if (tdep->has_gcs ())
-    set_gdbarch_ssp_regnum (gdbarch, tdep->gcs_reg_base);
+    {
+      /* AArch64's shadow stack pointer is the GCSPR.  */
+      set_gdbarch_ssp_regnum (gdbarch, tdep->gcs_reg_base);
+    }
+
+  /* Implementing this hook is required to allow the unwinding of
+     the shadow stack pointer in shadow-stack.c:dwarf2_prev_ssp.  */
+  set_gdbarch_top_addr_empty_shadow_stack
+    (gdbarch, aarch64_top_addr_empty_shadow_stack);
 
   /* ABI */
   set_gdbarch_short_bit (gdbarch, 16);
-- 
2.53.0

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