Re: [PATCH v1] gdb/aarch64: Add support for FEAT_S1POE POR_EL0 register

[Ezra Sitorus <ezra.sitorus@arm.com>]

On the whole it looks OK, these are just some observations from me.  I haven't
tested it yet, I can do so later.  Also, I can't give the final approval.

On Wed, Jun 17, 2026 at 05:00:03PM +0000, srinath.parvathaneni@arm.com wrote:
> From: Srinath Parvathaneni <srinath.parvathaneni@arm.com>
> 
> Hi,
> 
> FEAT_S1POE introduces the POR_EL0 register. This patch adds
> support for POR_EL0 in both native GDB and gdbserver using
> NT_ARM_POE and HWCAP2_POE detection.
> 
> With this change, POR_EL0 is available through:
> * info registers
> * info registers por_el0
> * p $por_el0
> * p/x $por_el0
> 
> This patch also extends AArch64 SIGSEGV reporting for POE permission
> faults. When a fault is reported with SEGV_PKUERR, GDB displays the
> fault address together with the decoded POR_EL0 permissions associated
> with the protection key that generated the fault and the current thread
> ID.
> 
> Example:
> Program received signal SIGSEGV, Segmentation fault
> Protection overlay violation while accessing address 0x0000fffff7ff3000
> POR_EL0[Protection-Key=1] = r-x (3) Thread Id = 1.
> 0x0000aaaaaaaa0990 in main () at aarch64-poe-sigsegv.c:49
> 
> The gdb.arch/aarch64-poe.exp testcase verifies POR_EL0 register
> visibility and access. The gdb.arch/aarch64-poe-sigsegv.exp testcase
> verifies POE-specific SIGSEGV reporting and is marked unsupported when
> the required userspace or kernel support is not available.
> 
> The tests were run on Arm FVP with FEAT_S1POE support and a Linux
> kernel built with CONFIG_ARM64_POE enabled.
> 
> Please note:
> 1. Support for "set $por_el0" is not included in this patch.
> 2. POR_EL0 write support will be addressed separately.
> 
> Regression tested on aarch64-none-linux-gnu target and found
> no regressions.
> 
> Regards,
> Srinath
> ---
>  gdb/Makefile.in                               |  2 +
>  gdb/aarch64-linux-nat.c                       | 35 ++++++++++
>  gdb/aarch64-linux-tdep.c                      | 68 ++++++++++++++++++-
>  gdb/aarch64-tdep.c                            | 15 ++++
>  gdb/aarch64-tdep.h                            | 10 +++
>  gdb/arch/aarch64-poe.h                        | 35 ++++++++++
>  gdb/arch/aarch64.c                            |  4 ++
>  gdb/arch/aarch64.h                            |  7 +-
>  gdb/features/Makefile                         |  1 +
>  gdb/features/aarch64-poe.c                    | 68 +++++++++++++++++++
>  gdb/features/aarch64-poe.xml                  | 50 ++++++++++++++
>  gdb/linux-tdep.c                              |  9 ++-
>  gdb/nat/aarch64-poe.h                         | 49 +++++++++++++
>  gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.c  | 52 ++++++++++++++
>  .../gdb.arch/aarch64-poe-sigsegv.exp          | 51 ++++++++++++++
>  gdb/testsuite/gdb.arch/aarch64-poe.c          | 29 ++++++++
>  gdb/testsuite/gdb.arch/aarch64-poe.exp        | 44 ++++++++++++
>  gdb/testsuite/lib/gdb.exp                     | 55 +++++++++++++++
>  gdbserver/linux-aarch64-low.cc                | 20 ++++++
>  19 files changed, 598 insertions(+), 6 deletions(-)
>  create mode 100644 gdb/arch/aarch64-poe.h
>  create mode 100644 gdb/features/aarch64-poe.c
>  create mode 100644 gdb/features/aarch64-poe.xml
>  create mode 100644 gdb/nat/aarch64-poe.h
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.c
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.exp
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-poe.c
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-poe.exp
> 
> diff --git a/gdb/Makefile.in b/gdb/Makefile.in
> index 57f384170ab..6cdc896d342 100644
> --- a/gdb/Makefile.in
> +++ b/gdb/Makefile.in
> @@ -1292,6 +1292,7 @@ HFILES_NO_SRCDIR = \
>  	arch/aarch32.h \
>  	arch/aarch64-fpmr-linux.h \
>  	arch/aarch64-gcs-linux.h \
> +	arch/aarch64-poe.h \
>  	arch/aarch64.h \
>  	arch/aarch64-insn.h \
>  	arch/aarch64-mte.h \
> @@ -1540,6 +1541,7 @@ HFILES_NO_SRCDIR = \
>  	namespace.h \
>  	nat/aarch64-fpmr-linux.h \
>  	nat/aarch64-gcs-linux.h \
> +	nat/aarch64-poe.h \
>  	nat/aarch64-hw-point.h \
>  	nat/aarch64-linux.h \
>  	nat/aarch64-linux-hw-point.h \
> diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
> index 52ace4aab41..181f3596481 100644
> --- a/gdb/aarch64-linux-nat.c
> +++ b/gdb/aarch64-linux-nat.c
> @@ -34,6 +34,7 @@
>  #include "arch/arm.h"
>  #include "nat/aarch64-fpmr-linux.h"
>  #include "nat/aarch64-gcs-linux.h"
> +#include "nat/aarch64-poe.h"
>  #include "nat/aarch64-linux.h"
>  #include "nat/aarch64-linux-hw-point.h"
>  #include "nat/aarch64-mte-linux-ptrace.h"
> @@ -569,6 +570,30 @@ fetch_gcsregs_from_thread (regcache *regcache)
>  			&user_gcs.features_locked);
>  }
>  
> +/* Fill GDB's register array with the POE register value from the current
> +   thread.  */
> +
> +static void
> +fetch_por_el0_from_thread (regcache *regcache)
> +{
> +  aarch64_gdbarch_tdep *tdep
> +    = gdbarch_tdep<aarch64_gdbarch_tdep> (regcache->arch ());
> +
> +  gdb_assert (tdep->poe_regnum != -1);
> +
> +  user_poe user_poe;
> +  iovec iovec;
> +
> +  iovec.iov_base = &user_poe;
> +  iovec.iov_len = sizeof (user_poe);
> +
> +  int tid = get_ptrace_pid (regcache->ptid ());
> +  if (ptrace (PTRACE_GETREGSET, tid, NT_ARM_POE, &iovec) != 0)
> +    perror_with_name (_("Unable to fetch POE register"));
> +
> +  regcache->raw_supply (tdep->poe_regnum, &user_poe.por_el0);
> +}
> +
>  /* Store to the current thread the valid GCS register set in the GDB's
>     register array.  */
>  
> @@ -683,6 +708,9 @@ aarch64_fetch_registers (struct regcache *regcache, int regno)
>        if (tdep->has_gcs_linux ())
>  	fetch_gcsregs_from_thread (regcache);
>  
> +      if (tdep->has_poe ())
> +	fetch_por_el0_from_thread (regcache);
> +
>        if (tdep->has_fpmr ())
>  	fetch_fpmr_from_thread (regcache);
>      }
> @@ -722,6 +750,10 @@ aarch64_fetch_registers (struct regcache *regcache, int regno)
>  	   && (regno == tdep->gcs_reg_base || regno == tdep->gcs_linux_reg_base
>  	       || regno == tdep->gcs_linux_reg_base + 1))
>      fetch_gcsregs_from_thread (regcache);
> +  /* POE register?  */
> +  else if (tdep->has_poe () && (regno == tdep->poe_regnum))
> +    fetch_por_el0_from_thread (regcache);
> +
>    /* FPMR?  */
>    else if (tdep->has_fpmr () && (regno == tdep->fpmr_regnum))
>      fetch_fpmr_from_thread (regcache);
> @@ -1024,6 +1056,9 @@ aarch64_linux_nat_target::read_description ()
>    /* Check for FPMR.  */
>    features.fpmr = hwcap2 & HWCAP2_FPMR;
>  
> +  /* Check for POE support.  */
> +  features.poe = hwcap2 & HWCAP2_POE;
> +
>    return aarch64_read_description (features);
>  }
>  
> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
> index f11eccc1bc1..be6ef8db526 100644
> --- a/gdb/aarch64-linux-tdep.c
> +++ b/gdb/aarch64-linux-tdep.c
> @@ -53,6 +53,7 @@
>  
>  #include "arch/aarch64-fpmr-linux.h"
>  #include "arch/aarch64-gcs-linux.h"
> +#include "arch/aarch64-poe.h"
>  #include "arch/aarch64-mte.h"
>  #include "arch/aarch64-mte-linux.h"
>  #include "arch/aarch64-pauth-linux.h"
> @@ -66,6 +67,7 @@
>  #include "elf/common.h"
>  #include "elf/aarch64.h"
>  #include "arch/aarch64-insn.h"
> +#include "gdbthread.h"
>  
>  /* For std::pow */
>  #include <cmath>
> @@ -274,6 +276,31 @@ struct aarch64_linux_sigframe
>  
>  };
>  
> +/* Convert a POR_EL0 Perm<m> overlay permission encoding into rwx-style string.
> +   For example:
> +     0b0011 -> "r-x" (3)
> +     0b0101 -> "rw-" (5)
> +     0b0111 -> "rwx" (7)
> +     0b0000 -> "---" (0)
> +   Reserved encodings (0b1xxx) are returned as "???".  */
> +
> +static const char*
> +aarch64_perm_overlay_decode (unsigned int perm)
> +{
> +  switch (perm)
> +   {
> +     case 0: return "---";
> +     case 1: return "r--";
> +     case 2: return "--x";
> +     case 3: return "r-x";
> +     case 4: return "-w-";
> +     case 5: return "rw-";
> +     case 6: return "-wx";
> +     case 7: return "rwx";
> +     default: return "???";
> +   }
> +}
> +
>  /* Read an aarch64_ctx, returning the magic value, and setting *SIZE to the
>     size, or return 0 on error.  */
>  
> @@ -2675,11 +2702,12 @@ aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
>  {
>    aarch64_gdbarch_tdep *tdep = gdbarch_tdep<aarch64_gdbarch_tdep> (gdbarch);
>  
> -  if (!(tdep->has_mte () || tdep->has_gcs ()) || siggnal != GDB_SIGNAL_SEGV)
> +  if (!(tdep->has_mte () || tdep->has_gcs () || tdep->has_poe ())
> +      || siggnal != GDB_SIGNAL_SEGV)
>      return;
>  
>    CORE_ADDR fault_addr = 0;
> -  long si_code = 0, si_errno = 0;
> +  long si_code = 0, si_errno = 0, si_pkey = -1;
>  
>    try
>      {
> @@ -2687,6 +2715,8 @@ aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
>  	 violation.  */
>        si_code = parse_and_eval_long ("$_siginfo.si_code");
>        si_errno = parse_and_eval_long ("$_siginfo.si_errno");
> +      if (tdep->has_poe ())
> +	si_pkey = parse_and_eval_long ("$_siginfo._sifields._sigfault.si_pkey");
>  
>        fault_addr
>  	= parse_and_eval_long ("$_siginfo._sifields._sigfault.si_addr");
> @@ -2703,6 +2733,8 @@ aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
>      meaning = _("Memory tag violation");
>    else if (si_code == AARCH64_SEGV_CPERR && si_errno == 0)
>      meaning = _("Guarded Control Stack error");
> +  else if (si_code == AARCH64_SEGV_PKUERR && si_errno == 0)
> +    meaning = _("Protection overlay violation");
>    else
>      return;
>  
> @@ -2734,6 +2766,36 @@ aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
>  	  uiout->field_string ("logical-tag", hex_string (ltag));
>  	}
>      }
> +  /* For POE SEGSEGV, show additional information.  */
> +  else if (si_code == AARCH64_SEGV_PKUERR)
> +    {
> +      frame_info_ptr frame = get_selected_frame (nullptr);
> +      value *v = value_of_register (tdep->poe_regnum, frame);
> +      ULONGEST por_el0 = (ULONGEST) value_as_long (v);
> +      unsigned int perm = (por_el0 >> (si_pkey * 4)) & 0xf;
> +
> +      uiout->text (_(" while accessing address "));
> +      uiout->field_core_addr ("fault-addr", gdbarch, fault_addr);
> +      uiout->text ("\n");
> +
> +      /* In the case of a SIGSEGV, print the POR_EL0[si_pkey] permission
> +	 associated with the faulting address as an rwx-style permission
> +	string, followed by its decimal value in parentheses and the
> +	current thread ID.
> +
> +	e.g. POR_EL0[Protection-Key=1] = r-x (3) Thread Id = 1.  */
> +

There's a minor issue with whitespacing here.

> +      uiout->text (_("POR_EL0[Protection-Key="));
> +      uiout->field_signed ("protection-key", si_pkey);
> +      uiout->text (_("] = "));
> +      uiout->text (aarch64_perm_overlay_decode (perm));
> +      uiout->text (" (");
> +      uiout->field_unsigned ("por-el0-permission", perm);
> +      uiout->text (")");
> +      thread_info *thr = inferior_thread ();
> +      uiout->text (" Thread Id = ");
> +      uiout->field_signed ("thread-id", thr->global_num);
> +    }
>    else if (si_code != AARCH64_SEGV_CPERR)
>      {
>        uiout->text ("\n");
> @@ -3054,7 +3116,7 @@ aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
>  					 aarch64_linux_decode_memtag_section);
>      }
>  
> -  if (tdep->has_mte () || tdep->has_gcs ())
> +  if (tdep->has_mte () || tdep->has_gcs () || tdep->has_poe ())
>      set_gdbarch_report_signal_info (gdbarch, aarch64_linux_report_signal_info);
>  
>    /* Initialize the aarch64_linux_record_tdep.  */
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index 886e7ce1e7b..23bca26ce43 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -4136,6 +4136,10 @@ aarch64_features_from_target_desc (const struct target_desc *tdesc)
>    features.fpmr = (tdesc_find_feature (tdesc, "org.gnu.gdb.aarch64.fpmr")
>  		   != nullptr);
>  
> +  /* Check for POE feature.  */
> +  features.poe = (tdesc_find_feature (tdesc, "org.gnu.gdb.aarch64.poe")
> +		   != nullptr);
> +
>    return features;
>  }
>  
> @@ -4556,6 +4560,16 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>  					  fpmr_regnum, "fpmr");
>      }
>  
> +  int poe_regnum = -1;
> +  const struct tdesc_feature *feature_poe
> +      = tdesc_find_feature (tdesc, "org.gnu.gdb.aarch64.poe");
> +  if (feature_poe != nullptr)
> +    {
> +      poe_regnum = num_regs++;
> +      valid_p &= tdesc_numbered_register (feature_poe, tdesc_data.get (),
> +					  poe_regnum, "por_el0");
> +    }
> +
>    int first_sme_regnum = -1;
>    int first_sme2_regnum = -1;
>    int first_sme_pseudo_regnum = -1;
> @@ -4755,6 +4769,7 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>    tdep->tls_register_count = tls_register_count;
>    tdep->gcs_reg_base = first_gcs_regnum;
>    tdep->gcs_linux_reg_base = first_gcs_linux_regnum;
> +  tdep->poe_regnum = poe_regnum;
>    tdep->fpmr_regnum = fpmr_regnum;
>  
>    /* Set the SME register set details.  The pseudo-registers will be adjusted
> diff --git a/gdb/aarch64-tdep.h b/gdb/aarch64-tdep.h
> index dff05a08f84..3b959132ca6 100644
> --- a/gdb/aarch64-tdep.h
> +++ b/gdb/aarch64-tdep.h
> @@ -208,6 +208,16 @@ struct aarch64_gdbarch_tdep : gdbarch_tdep_base
>      return gcs_linux_reg_base != -1;
>    }
>  
> +  /* First POE register.  This is -1 if no POE feature is available.  */
> +  int poe_regnum = -1;
> +
> +  /* Returns true if the target supports the Linux POE feature.  */
> +  bool
> +  has_poe () const
> +  {
> +    return poe_regnum != -1;
> +  }
> +
>    /* First FPMR register.  This is -1 if FPMR is not supported.  */
>    int fpmr_regnum = -1;
>  
> diff --git a/gdb/arch/aarch64-poe.h b/gdb/arch/aarch64-poe.h
> new file mode 100644
> index 00000000000..1f2ac5c0cd2
> --- /dev/null
> +++ b/gdb/arch/aarch64-poe.h
> @@ -0,0 +1,35 @@
> +/* Common Linux target-dependent definitions for AArch64 POE
> +
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +
> +   This file is part of GDB.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program 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 General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +#ifndef GDB_ARCH_AARCH64_POE_H
> +#define GDB_ARCH_AARCH64_POE_H
> +
> +/* Feature check for Permission Overlay Extension.  */
> +#ifndef HWCAP2_POE
> +#define AARCH64_HWCAP2_POE (1ULL << 63)
> +#endif
> +
> +#ifndef AARCH64_SEGV_PKUERR
> +#define AARCH64_SEGV_PKUERR 4  /* Protection overlay violation.  */
> +#endif
> +
> +/* The POE regset consists of 1 64-bit register.  */
> +#define AARCH64_LINUX_SIZEOF_POE_REGSET (8)
> +
> +#endif /* GDB_ARCH_AARCH64_POE_H */
> diff --git a/gdb/arch/aarch64.c b/gdb/arch/aarch64.c
> index 2401a325b7b..a567938d06d 100644
> --- a/gdb/arch/aarch64.c
> +++ b/gdb/arch/aarch64.c
> @@ -28,6 +28,7 @@
>  #include "../features/aarch64-sme2.c"
>  #include "../features/aarch64-tls.c"
>  #include "../features/aarch64-gcs.c"
> +#include "../features/aarch64-poe.c"
>  #include "../features/aarch64-gcs-linux.c"
>  
>  /* See arch/aarch64.h.  */
> @@ -77,6 +78,9 @@ aarch64_create_target_description (const aarch64_features &features)
>    if (features.fpmr)
>      regnum = create_feature_aarch64_fpmr (tdesc.get (), regnum);
>  
> +  if (features.poe)
> +    regnum = create_feature_aarch64_poe (tdesc.get (), regnum);
> +
>    return tdesc;
>  }
>  
> diff --git a/gdb/arch/aarch64.h b/gdb/arch/aarch64.h
> index cf7318cbe74..4e4b50f729e 100644
> --- a/gdb/arch/aarch64.h
> +++ b/gdb/arch/aarch64.h
> @@ -35,6 +35,7 @@ struct aarch64_features
>    bool pauth = false;
>    bool mte = false;
>    bool fpmr = false;
> +  bool poe = false;
>  
>    /* A positive TLS value indicates the number of TLS registers available.  */
>    uint8_t tls = 0;
> @@ -70,7 +71,8 @@ inline bool operator==(const aarch64_features &lhs, const aarch64_features &rhs)
>      && lhs.sme2 == rhs.sme2
>      && lhs.gcs == rhs.gcs
>      && lhs.gcs_linux == rhs.gcs_linux
> -    && lhs.fpmr == rhs.fpmr;
> +    && lhs.fpmr == rhs.fpmr
> +    && lhs.poe == rhs.poe;
>  }
>  
>  namespace std
> @@ -103,6 +105,9 @@ namespace std
>  
>        /* FPMR feature.  */
>        h = h << 1 | features.fpmr;
> +
> +      /* POE feature.  */
> +      h = h << 1 | features.poe;
>        return h;
>      }
>    };
> diff --git a/gdb/features/Makefile b/gdb/features/Makefile
> index 161a7453d66..cc77e5bb652 100644
> --- a/gdb/features/Makefile
> +++ b/gdb/features/Makefile
> @@ -207,6 +207,7 @@ FEATURE_XMLFILES = aarch64-core.xml \
>  	aarch64-pauth.xml \
>  	aarch64-mte.xml \
>  	aarch64-gcs.xml \
> +	aarch64-poe.xml \
>  	aarch64-gcs-linux.xml \
>  	arc/v1-core.xml \
>  	arc/v1-aux.xml \
> diff --git a/gdb/features/aarch64-poe.c b/gdb/features/aarch64-poe.c
> new file mode 100644
> index 00000000000..6892b52c1cf
> --- /dev/null
> +++ b/gdb/features/aarch64-poe.c
> @@ -0,0 +1,68 @@
> +/* THIS FILE IS GENERATED.  -*- buffer-read-only: t -*- vi:set ro:
> +  Original: aarch64-poe.xml */
> +
> +#include "gdbsupport/tdesc.h"
> +
> +static int
> +create_feature_aarch64_poe (struct target_desc *result, long regnum)
> +{
> +  struct tdesc_feature *feature;
> +
> +  feature = tdesc_create_feature (result, "org.gnu.gdb.aarch64.poe");
> +  tdesc_type_with_fields *type_with_fields;
> +  type_with_fields = tdesc_create_enum (feature, "por_el0_fmt", 4);
> +  tdesc_add_enum_value (type_with_fields, 0, "---");
> +  tdesc_add_enum_value (type_with_fields, 1, "r--");
> +  tdesc_add_enum_value (type_with_fields, 2, "--x");
> +  tdesc_add_enum_value (type_with_fields, 3, "r-x");
> +  tdesc_add_enum_value (type_with_fields, 4, "-w-");
> +  tdesc_add_enum_value (type_with_fields, 5, "rw-");
> +  tdesc_add_enum_value (type_with_fields, 6, "-wx");
> +  tdesc_add_enum_value (type_with_fields, 7, "rwx");
> +  tdesc_add_enum_value (type_with_fields, 8, "???");
> +  tdesc_add_enum_value (type_with_fields, 9, "???");
> +  tdesc_add_enum_value (type_with_fields, 10, "???");
> +  tdesc_add_enum_value (type_with_fields, 11, "???");
> +  tdesc_add_enum_value (type_with_fields, 12, "???");
> +  tdesc_add_enum_value (type_with_fields, 13, "???");
> +  tdesc_add_enum_value (type_with_fields, 14, "???");
> +  tdesc_add_enum_value (type_with_fields, 15, "???");
> +
> +  type_with_fields = tdesc_create_flags (feature, "por_el0_flags", 8);
> +  tdesc_type *field_type;
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "Pf", 60, 63, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "Pe", 56, 59, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "Pd", 52, 55, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "Pc", 48, 51, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "Pb", 44, 47, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "Pa", 40, 43, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P9", 36, 39, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P8", 32, 35, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P7", 28, 31, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P6", 24, 27, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P5", 20, 23, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P4", 16, 19, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P3", 12, 15, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P2", 8, 11, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P1", 4, 7, field_type);
> +  field_type = tdesc_named_type (feature, "por_el0_fmt");
> +  tdesc_add_typed_bitfield (type_with_fields, "P0", 0, 3, field_type);
> +
> +  tdesc_create_reg (feature, "por_el0", regnum++, 1, "system", 64, "por_el0_flags");
> +  return regnum;
> +}
> diff --git a/gdb/features/aarch64-poe.xml b/gdb/features/aarch64-poe.xml
> new file mode 100644
> index 00000000000..e415a0f6bb6
> --- /dev/null
> +++ b/gdb/features/aarch64-poe.xml
> @@ -0,0 +1,50 @@
> +<?xml version="1.0"?>
> +<!-- Copyright (C) 2026 Free Software Foundation, Inc.
> +
> +     Copying and distribution of this file, with or without modification,
> +     are permitted in any medium without royalty provided the copyright
> +     notice and this notice are preserved.  -->
> +
> +<!DOCTYPE feature SYSTEM "gdb-target.dtd">
> +<feature name="org.gnu.gdb.aarch64.poe">
> +
> +  <enum id="por_el0_fmt" size="4">
> +    <evalue name="---" value="0"/>
> +    <evalue name="r--" value="1"/>
> +    <evalue name="--x" value="2"/>
> +    <evalue name="r-x" value="3"/>
> +    <evalue name="-w-" value="4"/>
> +    <evalue name="rw-" value="5"/>
> +    <evalue name="-wx" value="6"/>
> +    <evalue name="rwx" value="7"/>
> +    <evalue name="???" value="8"/>
> +    <evalue name="???" value="9"/>
> +    <evalue name="???" value="10"/>
> +    <evalue name="???" value="11"/>
> +    <evalue name="???" value="12"/>
> +    <evalue name="???" value="13"/>
> +    <evalue name="???" value="14"/>
> +    <evalue name="???" value="15"/>
> +  </enum>
> +
> +  <flags id="por_el0_flags" size="8">
> +    <field name="Pf" start="60" end="63" type="por_el0_fmt"/>
> +    <field name="Pe" start="56" end="59" type="por_el0_fmt"/>
> +    <field name="Pd" start="52" end="55" type="por_el0_fmt"/>
> +    <field name="Pc" start="48" end="51" type="por_el0_fmt"/>
> +    <field name="Pb" start="44" end="47" type="por_el0_fmt"/>
> +    <field name="Pa" start="40" end="43" type="por_el0_fmt"/>
> +    <field name="P9" start="36" end="39" type="por_el0_fmt"/>
> +    <field name="P8" start="32" end="35" type="por_el0_fmt"/>
> +    <field name="P7" start="28" end="31" type="por_el0_fmt"/>
> +    <field name="P6" start="24" end="27" type="por_el0_fmt"/>
> +    <field name="P5" start="20" end="23" type="por_el0_fmt"/>
> +    <field name="P4" start="16" end="19" type="por_el0_fmt"/>
> +    <field name="P3" start="12" end="15" type="por_el0_fmt"/>
> +    <field name="P2" start="8" end="11" type="por_el0_fmt"/>
> +    <field name="P1" start="4" end="7" type="por_el0_fmt"/>
> +    <field name="P0" start="0" end="3" type="por_el0_fmt"/>
> +  </flags>
> +
> +  <reg name="por_el0" bitsize="64" type="por_el0_flags" group="system"/>
> +</feature>
> diff --git a/gdb/linux-tdep.c b/gdb/linux-tdep.c
> index a7381677498..44236ebe86e 100644
> --- a/gdb/linux-tdep.c
> +++ b/gdb/linux-tdep.c
> @@ -366,8 +366,13 @@ linux_get_siginfo_type (struct gdbarch *gdbarch)
>  
>    /* _sigfault */
>    type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
> -  append_composite_type_field (type, "si_addr", void_ptr_type);
> -  append_composite_type_field (sifields_type, "_sigfault", type);
> +   {
> +     int size_of_ptr = gdbarch_ptr_bit (gdbarch) / HOST_CHAR_BIT;
> +     append_composite_type_field (type, "si_addr", void_ptr_type);
> +     append_composite_type_field (type, "_pad", init_vector_type (builtin_type (gdbarch)->builtin_char, size_of_ptr));
> +     append_composite_type_field (type, "si_pkey", builtin_type (gdbarch)->builtin_uint32);
> +     append_composite_type_field (sifields_type, "_sigfault", type);
> +   }
>  
>    /* _sigpoll */
>    type = arch_composite_type (gdbarch, NULL, TYPE_CODE_STRUCT);
> diff --git a/gdb/nat/aarch64-poe.h b/gdb/nat/aarch64-poe.h
> new file mode 100644
> index 00000000000..3221634fd25
> --- /dev/null
> +++ b/gdb/nat/aarch64-poe.h
> @@ -0,0 +1,49 @@
> +/* Common native Linux definitions for AArch64 Permission Overlay Extension.
> +
> +   Copyright (C) 2026 Free Software Foundation, Inc.
> +
> +   This file is part of GDB.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program 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 General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +#ifndef GDB_NAT_AARCH64_POE_H
> +#define GDB_NAT_AARCH64_POE_H
> +
> +#include <stdint.h>
> +#include <asm/hwcap.h>
> +#include <asm/ptrace.h>
> +
> +/* Feature check for Permission Overlay Extension.  */
> +#ifndef HWCAP2_POE
> +#define HWCAP2_POE (1ULL << 63)
> +#endif
> +
> +#ifndef HAVE_STRUCT_USER_POE
> +
> +/* POE state (NT_ARM_POE).  */
> +#ifndef NT_ARM_POE
> +#define NT_ARM_POE 0x40f
> +#endif
> +
> +struct user_poe
> +{
> +  uint64_t por_el0;
> +};
> +

Any particular reason as to why a struct is used here?  From looking at kernel,
I don't think there's any more fields to be added.

> +#endif /* HAVE_STRUCT_USER_POE */
> +
> +/* The POE regset consists of 1 64-bit register.  */
> +#define AARCH64_LINUX_SIZEOF_POE_REGSET (8)
> +
> +#endif /* GDB_NAT_AARCH64_POE_H */
> diff --git a/gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.c b/gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.c
> new file mode 100644
> index 00000000000..6b0c07e782f
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.c
> @@ -0,0 +1,52 @@
> +/* This test program is part of GDB, the GNU debugger.
> +
> +   Copyright 2026 Free Software Foundation, Inc.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program 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 General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +/* Exercise AArch64's POE Extension.  */
> +
> +/* This test is based on the Linux kernel documentation for Memory
> +   Protection Keys, including the arm64 Permission Overlay Extension
> +   (FEAT_S1POE) support described in
> +   Documentation/core-api/protection-keys.rst.  */
> +
> +#define _GNU_SOURCE
> +#include <sys/mman.h>
> +#include <unistd.h>
> +
> +int
> +main (void)
> +{
> +  long pagesize = sysconf (_SC_PAGESIZE);
> +
> +  int *buf = mmap (NULL, pagesize, PROT_READ | PROT_WRITE,
> +		   MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +  if (buf == MAP_FAILED)
> +    return 1;
> +
> +  int pkey = pkey_alloc (0, 0);
> +  if (pkey == -1)
> +    return 1;
> +
> +  if (pkey_mprotect (buf, pagesize, PROT_READ | PROT_WRITE, pkey) == -1)
> +    return 1;
> +
> +  if (pkey_set (pkey, PKEY_DISABLE_WRITE) == -1)
> +    return 1;
> +
> +  buf[0] = 42;  /* Expect SIGSEGV POE violation.  */
> +
> +  return 1;
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.exp b/gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.exp
> new file mode 100644
> index 00000000000..dfd91f652f0
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-poe-sigsegv.exp
> @@ -0,0 +1,51 @@
> +# Copyright (C) 2026 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program 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 General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# Test a binary that uses POE and exposed POR_EL0 register.
> +
> +global hex
> +global decimal
> +
> +require is_aarch64_target
> +
> +if {![allow_aarch64_poe_tests]} {
> +    unsupported "AArch64 POE not supported"
> +    return
> +}
> +
> +standard_testfile
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> +    return
> +}
> +
> +if {![runto_main]} {
> +    return
> +}
> +
> +# Display POE violation SIGSEGV error message.
> +set poe_sigsegv_re [multi_line \
> +    "Program received signal SIGSEGV, Segmentation fault" \
> +    "Protection overlay violation while accessing address ${hex}" \
> +    "POR_EL0\\\[Protection-Key=${decimal}\\\] = \[-rwx\]+ \\(${decimal}\\) Thread Id = ${decimal}"]
> +
> +gdb_test_multiple "continue" "display POE violation information" {
> +    -re "$poe_sigsegv_re.*$gdb_prompt $" {
> +	pass $gdb_test_name
> +    }
> +
> +    -re ".*exited with code 01.*$gdb_prompt $" {
> +	unsupported "POE userspace support unavailable"
> +    }
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-poe.c b/gdb/testsuite/gdb.arch/aarch64-poe.c
> new file mode 100644
> index 00000000000..2c95dc2a99b
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-poe.c
> @@ -0,0 +1,29 @@
> +/* This test program is part of GDB, the GNU debugger.
> +
> +   Copyright 2026 Free Software Foundation, Inc.
> +
> +   This program is free software; you can redistribute it and/or modify
> +   it under the terms of the GNU General Public License as published by
> +   the Free Software Foundation; either version 3 of the License, or
> +   (at your option) any later version.
> +
> +   This program 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 General Public License for more details.
> +
> +   You should have received a copy of the GNU General Public License
> +   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
> +
> +/* Exercise AArch64's POE Extension.  */
> +
> +/* This test is based on the Linux kernel documentation for Memory
> +   Protection Keys, including the arm64 Permission Overlay Extension
> +   (FEAT_S1POE) support described in
> +   Documentation/core-api/protection-keys.rst.  */
> +
> +int
> +main (void)
> +{
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-poe.exp b/gdb/testsuite/gdb.arch/aarch64-poe.exp
> new file mode 100644
> index 00000000000..ae2663a7dbc
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-poe.exp
> @@ -0,0 +1,44 @@
> +# Copyright (C) 2026 Free Software Foundation, Inc.
> +
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 3 of the License, or
> +# (at your option) any later version.
> +#
> +# This program 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 General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program.  If not, see <http://www.gnu.org/licenses/>.
> +
> +# Test a binary that uses POE and exposed POR_EL0 register.
> +
> +global hex
> +global decimal
> +
> +require is_aarch64_target
> +
> +if {![allow_aarch64_poe_tests]} {
> +    unsupported "AArch64 POE not supported"
> +    return
> +}
> +
> +standard_testfile
> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
> +    return
> +}
> +
> +if {![runto_main]} {
> +    return
> +}
> +
> +# Validate the presence of the POE register.
> +    gdb_test "info registers por_el0" \
> +	     "por_el0\[ \t\]+$hex.*" \
> +	     "register por_el0 available"
> +
> +    gdb_test "p/x \$por_el0" \
> +	     "\\$\[0-9\]+ = ${hex}" \
> +	     "print por_el0"
> diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
> index 7b1feeaac84..fe2c533791c 100644
> --- a/gdb/testsuite/lib/gdb.exp
> +++ b/gdb/testsuite/lib/gdb.exp
> @@ -5616,6 +5616,61 @@ gdb_caching_proc allow_aarch64_gcs_tests {} {
>      return $allow_gcs_tests
>  }
>  
> +# Run a test on the target to see if it supports AArch64 POE extensions.
> +# Return 1 if so, 0 if it does not.  Note this causes a restart of GDB.
> +
> +gdb_caching_proc allow_aarch64_poe_tests {} {
> +    global srcdir subdir gdb_prompt inferior_exited_re
> +
> +    set me "allow_aarch64_poe_tests"
> +
> +    if { ![is_aarch64_target]} {
> +	return 0
> +    }
> +
> +    # Compile a program that tests the POE feature.
> +    set src {
> +	#include <stdbool.h>
> +	#include <sys/auxv.h>
> +
> +	/* Feature check for POE feature.  */
> +	#ifndef HWCAP2_POE
> +	#define HWCAP2_POE (1ULL << 63)
> +	#endif
> +
> +	int main (void) {
> +	    bool poe_supported = getauxval (AT_HWCAP2) & HWCAP2_POE;
> +
> +	    /* Return success if POE is supported.  */
> +	    return !poe_supported;
> +	}
> +    }
> +
> +    if {![gdb_simple_compile $me $src executable]} {
> +	return 0
> +    }
> +
> +    # Compilation succeeded so now run it via gdb.
> +    set allow_poe_tests 0
> +    clean_restart
> +    gdb_load $obj
> +    gdb_run_cmd
> +    gdb_expect {
> +	-re ".*$inferior_exited_re normally.*${gdb_prompt} $" {
> +	    verbose -log "\n$me: poe support detected"
> +	    set allow_poe_tests 1
> +	}
> +	-re ".*$inferior_exited_re with code 01.*${gdb_prompt} $" {
> +	    verbose -log "\n$me: poe support not detected"
> +	}
> +    }
> +    gdb_exit
> +    remote_file build delete $obj
> +
> +    verbose "$me:  returning $allow_poe_tests" 2
> +    return $allow_poe_tests
> +}
> +
>  # A helper that compiles a test case to see if __int128 is supported.
>  proc gdb_int128_helper {lang} {
>      return [gdb_can_simple_compile "i128-for-$lang" {
> diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
> index a2588a6e2a9..c27525be1ac 100644
> --- a/gdbserver/linux-aarch64-low.cc
> +++ b/gdbserver/linux-aarch64-low.cc
> @@ -45,6 +45,7 @@
>  #include "linux-aarch32-tdesc.h"
>  #include "linux-aarch64-tdesc.h"
>  #include "nat/aarch64-fpmr-linux.h"
> +#include "nat/aarch64-poe.h"
>  #include "nat/aarch64-gcs-linux.h"
>  #include "nat/aarch64-mte-linux-ptrace.h"
>  #include "nat/aarch64-scalable-linux-ptrace.h"
> @@ -250,6 +251,16 @@ aarch64_store_fpregset (struct regcache *regcache, const void *buf)
>    supply_register (regcache, AARCH64_FPCR_REGNUM, &regset->fpcr);
>  }
>  
> +/* Store the POE (POR_EL0) register set to regcache.  */
> +
> +static void
> +aarch64_store_por_el0_regset (struct regcache *regcache, const void *buf)
> +{
> +  const user_poe *regset = (const user_poe *) buf;
> +  int poe_regnum  = find_regno (regcache->tdesc, "por_el0");

I've noticed that a few of the regnum have 2 spaces before the '=' (gcspr,
features_enabled).  I'm not sure if this is intentional or not.

> +  supply_register (regcache, poe_regnum, &regset->por_el0);
> +}
> +
>  /* Fill BUF with the FPMR register set from the regcache.  */
>  
>  static void
> @@ -901,6 +912,10 @@ static struct regset_info aarch64_regsets[] =
>    { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_ARM_FPMR,
>      0, OPTIONAL_REGS,
>      aarch64_fill_fpmr_regset, aarch64_store_fpmr_regset },
> +  /* POE register (POR_EL0).  */
> +  { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_ARM_POE,
> +    0, OPTIONAL_REGS,
> +    nullptr, aarch64_store_por_el0_regset },
>    /* TLS register.  */
>    { PTRACE_GETREGSET, PTRACE_SETREGSET, NT_ARM_TLS,
>      0, OPTIONAL_REGS,
> @@ -980,6 +995,10 @@ aarch64_adjust_register_sets (const struct aarch64_features &features)
>  	  if (features.fpmr)
>  	    regset->size = sizeof (uint64_t);
>  	  break;
> +	case NT_ARM_POE:
> +	  if (features.poe)
> +	    regset->size = sizeof (user_poe);
> +	  break;
>  	default:
>  	  gdb_assert_not_reached ("Unknown register set found.");
>  	}
> @@ -1010,6 +1029,7 @@ aarch64_target::low_arch_setup ()
>        features.tls = aarch64_tls_register_count (tid);
>        features.gcs = features.gcs_linux = linux_get_hwcap (pid, 8) & HWCAP_GCS;
>        features.fpmr = linux_get_hwcap2 (pid, 8) & HWCAP2_FPMR;
> +      features.poe = linux_get_hwcap2 (pid, 8) & HWCAP2_POE;
>  
>        /* Scalable Matrix Extension feature and size check.  */
>        if (linux_get_hwcap2 (pid, 8) & HWCAP2_SME)
> -- 
> 2.43.0
>