GDB: aarch64: Fix inferior function call if GCS is present but disabled

On AArch64, even if the Guarded Control Stack feature is present on the
system the inferior may not have enabled it.

There's a bug in GDB's GCS support in that if the system supports GCS,
GDB will always push a GCS entry when doing an inferior function call
even if the inferior doesn't have it enabled.  This causes inferior
function calls to fail. E.g.:

  (gdb) p foo ()
  Can't write to Guarded Control Stack.

The error message is because the GCSPR doesn't point to a valid memory
address.

Fix by checking whether GCS is enabled in the inferior before trying to
push a GCS entry.

Regression tested on an aarch64-linux-gnu QEMU VM with GCS present.

Approved-By: Luis Machado <luis.machado.foss@gmail.com>

diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
index a84da1fd59eb94ee792a633b8aeb371091dc7bca..950ad4f6aaeb592161a3ccc1da8f469b762d0ad2 100644 (file)
--- a/gdb/aarch64-tdep.c
+++ b/gdb/aarch64-tdep.c
@@ -1934,7 +1934,11 @@ static void
 aarch64_shadow_stack_push (gdbarch *gdbarch, CORE_ADDR new_addr,
                           regcache *regcache)
 {
-  aarch64_push_gcs_entry (regcache, new_addr);
+  bool gcs_is_enabled;
+
+  (void) gdbarch_get_shadow_stack_pointer (gdbarch, regcache, gcs_is_enabled);
+  if (gcs_is_enabled)
+    aarch64_push_gcs_entry (regcache, new_addr);
 }
 
 /* Implement the "push_dummy_call" gdbarch method.  */