gdb/arm: Remove tpidruro register from non-FreeBSD target descriptions

Commit 92d48a1e4e ("Add an arm-tls feature which includes the tpidruro
register from CP15.") introduced the org.gnu.gdb.arm.tls feature, which
adds the tpidruro register, and unconditionally enabled it in
aarch32_create_target_description.

In Linux, the tpidruro register isn't available via ptrace in the 32-bit
kernel but it is available for an aarch32 program running under an arm64
kernel via the ptrace compat interface.  This isn't currently implemented
however, which causes GDB on arm-linux with 64-bit kernel to list the
register but show it as unavailable, as reported by Tom de Vries:

  $ gdb -q -batch a.out -ex start -ex 'p $tpidruro'
  Temporary breakpoint 1 at 0x512

  Temporary breakpoint 1, 0xaaaaa512 in main ()
  $1 = <unavailable>

Simon Marchi then clarified:

> The only time we should be seeing some "unavailable" registers or memory
> is in the context of tracepoints, for things that are not collected.
> Seeing an unavailable register here is a sign that something is not
> right.

Therefore, disable the TLS feature in aarch32 target descriptions for Linux
and NetBSD targets (the latter also doesn't seem to support accessing
tpidruro either, based on a quick look at arm-netbsd-nat.c).

This patch fixes the following tests:

Running gdb.base/inline-frame-cycle-unwind.exp ...
FAIL: gdb.base/inline-frame-cycle-unwind.exp: cycle at level 3: backtrace when the unwind is broken at frame 3
FAIL: gdb.base/inline-frame-cycle-unwind.exp: cycle at level 5: backtrace when the unwind is broken at frame 5
FAIL: gdb.base/inline-frame-cycle-unwind.exp: cycle at level 1: backtrace when the unwind is broken at frame 1

Tested with Ubuntu 22.04.3 on armv8l-linux-gnueabihf in native,
native-gdbserver and native-extended-gdbserver targets with no regressions.

PR tdep/31418
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=31418

Approved-By: John Baldwin <jhb@FreeBSD.org>

gdb/aarch32-tdep.c

@@ -22,15 +22,20 @@
 #include "gdbsupport/common-regcache.h"
 #include "arch/aarch32.h"
 
-static struct target_desc *tdesc_aarch32;
+static struct target_desc *tdesc_aarch32_list[2];
 
 /* See aarch32-tdep.h.  */
 
 const target_desc *
-aarch32_read_description ()
+aarch32_read_description (bool tls)
 {
-  if (tdesc_aarch32 == nullptr)
+  struct target_desc *tdesc = tdesc_aarch32_list[tls];
-    tdesc_aarch32 = aarch32_create_target_description ();
 
-  return tdesc_aarch32;
+  if (tdesc == nullptr)
+    {
+      tdesc = aarch32_create_target_description (tls);
+      tdesc_aarch32_list[tls] = tdesc;
+    }
+
+  return tdesc;
 }

gdb/aarch32-tdep.h

@@ -22,6 +22,6 @@ struct target_desc;
 
 /* Get the AArch32 target description.  */
 
-const target_desc *aarch32_read_description ();
+const target_desc *aarch32_read_description (bool tls);
 
 #endif /* aarch32-tdep.h.  */

gdb/aarch64-linux-nat.c

@@ -887,7 +887,7 @@ aarch64_linux_nat_target::read_description ()
 
   ret = ptrace (PTRACE_GETREGSET, tid, NT_ARM_VFP, &iovec);
   if (ret == 0)
-    return aarch32_read_description ();
+    return aarch32_read_description (false);
 
   CORE_ADDR hwcap = linux_get_hwcap ();
   CORE_ADDR hwcap2 = linux_get_hwcap2 ();

gdb/arch/aarch32.c

@@ -25,7 +25,7 @@
 /* See aarch32.h.  */
 
 target_desc *
-aarch32_create_target_description ()
+aarch32_create_target_description (bool tls)
 {
   target_desc_up tdesc = allocate_target_description ();
 
@@ -39,6 +39,7 @@ aarch32_create_target_description ()
   /* Create a vfpv3 feature, then a blank NEON feature.  */
   regnum = create_feature_arm_arm_vfpv3 (tdesc.get (), regnum);
   tdesc_create_feature (tdesc.get (), "org.gnu.gdb.arm.neon");
+  if (tls)
     regnum = create_feature_arm_arm_tls (tdesc.get (), regnum);
 
   return tdesc.release ();

gdb/arch/aarch32.h

@@ -22,6 +22,6 @@
 
 /* Create the AArch32 target description.  */
 
-target_desc *aarch32_create_target_description ();
+target_desc *aarch32_create_target_description (bool tls);
 
 #endif /* aarch32.h.  */

gdb/arm-fbsd-tdep.c

@@ -228,7 +228,7 @@ arm_fbsd_read_description_auxv (const std::optional<gdb::byte_vector> &auxv,
   if (arm_hwcap & HWCAP_VFP)
     {
       if (arm_hwcap & HWCAP_NEON)
-	return aarch32_read_description ();
+	return aarch32_read_description (tls);
       else if ((arm_hwcap & (HWCAP_VFPv3 | HWCAP_VFPD32))
 	       == (HWCAP_VFPv3 | HWCAP_VFPD32))
 	return arm_read_description (ARM_FP_TYPE_VFPV3, tls);

gdb/arm-linux-nat.c

@@ -568,7 +568,7 @@ arm_linux_nat_target::read_description ()
       /* NEON implies VFPv3-D32 or no-VFP unit.  Say that we only support
 	 Neon with VFPv3-D32.  */
       if (arm_hwcap & HWCAP_NEON)
-	return aarch32_read_description ();
+	return aarch32_read_description (false);
       else if ((arm_hwcap & (HWCAP_VFPv3 | HWCAP_VFPv3D16)) == HWCAP_VFPv3)
 	return arm_read_description (ARM_FP_TYPE_VFPV3, false);
 

gdb/arm-linux-tdep.c

@@ -740,7 +740,7 @@ arm_linux_core_read_description (struct gdbarch *gdbarch,
       /* NEON implies VFPv3-D32 or no-VFP unit.  Say that we only support
 	 Neon with VFPv3-D32.  */
       if (arm_hwcap & HWCAP_NEON)
-	return aarch32_read_description ();
+	return aarch32_read_description (false);
       else if ((arm_hwcap & (HWCAP_VFPv3 | HWCAP_VFPv3D16)) == HWCAP_VFPv3)
 	return arm_read_description (ARM_FP_TYPE_VFPV3, false);
 

gdb/arm-netbsd-nat.c

@@ -350,7 +350,7 @@ arm_netbsd_nat_target::read_description ()
 
   len = sizeof(flag);
   if (sysctlbyname("machdep.neon_present", &flag, &len, NULL, 0) == 0 && flag)
-    return aarch32_read_description ();
+    return aarch32_read_description (false);
 
   return arm_read_description (ARM_FP_TYPE_VFPV3, false);
 }

gdbserver/linux-aarch32-tdesc.cc

@@ -32,7 +32,7 @@ aarch32_linux_read_description ()
 {
   if (tdesc_aarch32 == nullptr)
     {
-      tdesc_aarch32 = aarch32_create_target_description ();
+      tdesc_aarch32 = aarch32_create_target_description (false);
 
       static const char *expedite_regs[] = { "r11", "sp", "pc", 0 };
       init_target_desc (tdesc_aarch32, expedite_regs);