aarch64: Enhanced CPU diagnostics for ld.so

This prints some information from struct cpu_features, and the midr_el1
and dczid_el0 system register contents on every CPU.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

manual/dynlink.texi

@@ -224,6 +224,40 @@ reflect adjustment by @theglibc{}.
 These Linux-specific items show the values of @code{struct utsname}, as
 reported by the @code{uname} function.  @xref{Platform Type}.
 
+@item aarch64.cpu_features.@dots{}
+These items are specific to the AArch64 architectures.  They report data
+@theglibc{} uses to activate conditionally supported features such as
+BTI and MTE, and to select alternative function implementations.
+
+@item aarch64.processor[@var{index}].@dots{}
+These are additional items for the AArch64 architecture and are
+described below.
+
+@item aarch64.processor[@var{index}].requested=@var{kernel-cpu}
+The kernel is told to run the subsequent probing on the CPU numbered
+@var{kernel-cpu}.  The values @var{kernel-cpu} and @var{index} can be
+distinct if there are gaps in the process CPU affinity mask.  This line
+is not included if CPU affinity mask information is not available.
+
+@item aarch64.processor[@var{index}].observed=@var{kernel-cpu}
+This line reports the kernel CPU number @var{kernel-cpu} on which the
+probing code initially ran.  If the CPU number cannot be obtained,
+this line is not printed.
+
+@item aarch64.processor[@var{index}].observed_node=@var{node}
+This reports the observed NUMA node number, as reported by the
+@code{getcpu} system call.  If this information cannot be obtained, this
+line is not printed.
+
+@item aarch64.processor[@var{index}].midr_el1=@var{value}
+The value of the @code{midr_el1} system register on the processor
+@var{index}.  This line is only printed if the kernel indicates that
+this system register is supported.
+
+@item aarch64.processor[@var{index}].dczid_el0=@var{value}
+The value of the @code{dczid_el0} system register on the processor
+@var{index}.
+
 @cindex CPUID (diagnostics)
 @item x86.cpu_features.@dots{}
 These items are specific to the i386 and x86-64 architectures.  They

sysdeps/aarch64/dl-diagnostics-cpu.c

@@ -0,0 +1,84 @@
+/* Print CPU diagnostics data in ld.so.  AArch64 version.
+   Copyright (C) 2021-2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <dl-diagnostics.h>
+
+#include <cpu-features.h>
+#include <dl-iterate_cpu.h>
+#include <ldsodefs.h>
+#include <sys/auxv.h>
+
+static void
+print_cpu_features_value (const char *label, uint64_t value)
+{
+  _dl_printf ("aarch64.cpu_features.");
+  _dl_diagnostics_print_labeled_value (label, value);
+}
+
+static void
+print_per_cpu_value (const struct dl_iterate_cpu *dic,
+                     const char *label, uint64_t value)
+{
+  _dl_printf ("aarch64.processor[0x%x].", dic->processor_index);
+  _dl_diagnostics_print_labeled_value (label, value);
+}
+
+void
+_dl_diagnostics_cpu (void)
+{
+  print_cpu_features_value ("bti", GLRO (dl_aarch64_cpu_features).bti);
+  print_cpu_features_value ("midr_el1",
+                            GLRO (dl_aarch64_cpu_features).midr_el1);
+  print_cpu_features_value ("mops", GLRO (dl_aarch64_cpu_features).mops);
+  print_cpu_features_value ("mte_state",
+                            GLRO (dl_aarch64_cpu_features).mte_state);
+  print_cpu_features_value ("prefer_sve_ifuncs",
+                            GLRO (dl_aarch64_cpu_features).prefer_sve_ifuncs);
+  print_cpu_features_value ("sve", GLRO (dl_aarch64_cpu_features).sve);
+  print_cpu_features_value ("zva_size",
+                            GLRO (dl_aarch64_cpu_features).zva_size);
+
+  struct dl_iterate_cpu dic;
+  _dl_iterate_cpu_init (&dic);
+
+  while (_dl_iterate_cpu_next (&dic))
+    {
+      if (dic.requested_cpu >= 0)
+        _dl_printf ("aarch64.processor[0x%x].requested=0x%x\n",
+                    dic.processor_index, dic.requested_cpu);
+      if (dic.actual_cpu >= 0)
+        _dl_printf ("aarch64.processor[0x%x].observed=0x%x\n",
+                    dic.processor_index, dic.actual_cpu);
+      if (dic.actual_node >= 0)
+        _dl_printf ("aarch64.processor[0x%x].observed_node=0x%x\n",
+                    dic.processor_index, dic.actual_node);
+
+      if (GLRO (dl_hwcap) & HWCAP_CPUID)
+        {
+          uint64_t midr_el1;
+          asm ("mrs %0, midr_el1" : "=r" (midr_el1));
+          print_per_cpu_value (&dic, "midr_el1", midr_el1);
+        }
+
+      {
+        uint64_t dczid_el0;
+        asm ("mrs %0, dczid_el0" : "=r" (dczid_el0));
+        print_per_cpu_value (&dic, "dczid_el0", dczid_el0);
+      }
+    }
+}