[Ping v2][PATCH,v2] [aarch64] Fix removal of non-address bits for PAuth

[Luis Machado <luis.machado@arm.com>]

On 7/18/22 09:16, Luis Machado wrote:
> On 7/11/22 12:55, Luis Machado via Gdb-patches wrote:
>> v2:
>>
>> - Renamed aarch64_remove_top_bytes to aarch64_remove_top_bits
>> - Formatting issues.
>>
>> -- 
>>
>> The address_significant gdbarch setting was introduced as a way to remove
>> non-address bits from pointers, and it is specified by a constant.  This
>> constant represents the number of address bits in a pointer.
>>
>> Right now AArch64 is the only architecture that uses it, and 56 was a
>> correct option so far.
>>
>> But if we are using Pointer Authentication (PAuth), we might use up to 2 bytes
>> from the address space to store the required information.  We could also have
>> cases where we're using both PAuth and MTE.
>>
>> We could adjust the constant to 48 to cover those cases, but this doesn't
>> cover the case where GDB needs to sign-extend kernel addresses after removal
>> of the non-address bits.
>>
>> This has worked so far because bit 55 is used to select between kernel-space
>> and user-space addresses.  But trying to clear a range of bits crossing the
>> bit 55 boundary requires the hook to be smarter.
>>
>> The following patch renames the gdbarch hook from significant_addr_bit to
>> remove_non_address_bits and passes a pointer as opposed to the number of
>> bits.  The hook is now responsible for removing the required non-address bits
>> and sign-extending the address if needed.
>>
>> While at it, make GDB and GDBServer share some more code for aarch64 and add a
>> new arch-specific testcase gdb.arch/aarch64-non-address-bits.exp.
>>
>> Bug-url: https://sourceware.org/bugzilla/show_bug.cgi?id=28947
>> ---
>>   gdb/aarch64-linux-nat.c                       |   2 +-
>>   gdb/aarch64-linux-tdep.c                      |  57 ++++++++-
>>   gdb/arch-utils.c                              |   8 ++
>>   gdb/arch-utils.h                              |   4 +
>>   gdb/arch/aarch64.c                            |  19 +++
>>   gdb/arch/aarch64.h                            |   9 ++
>>   gdb/breakpoint.c                              |   6 +-
>>   gdb/gdbarch-components.py                     |  20 ++-
>>   gdb/gdbarch-gen.h                             |  19 ++-
>>   gdb/gdbarch.c                                 |  25 ++--
>>   gdb/target.c                                  |   2 +-
>>   .../gdb.arch/aarch64-non-address-bits.c       |  25 ++++
>>   .../gdb.arch/aarch64-non-address-bits.exp     | 121 ++++++++++++++++++
>>   gdb/utils.c                                   |  22 ----
>>   gdb/utils.h                                   |   3 -
>>   gdbserver/linux-aarch64-low.cc                |  40 ++++--
>>   16 files changed, 309 insertions(+), 73 deletions(-)
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-non-address-bits.c
>>   create mode 100644 gdb/testsuite/gdb.arch/aarch64-non-address-bits.exp
>>
>> diff --git a/gdb/aarch64-linux-nat.c b/gdb/aarch64-linux-nat.c
>> index d58ad0143a2..3f41aae188e 100644
>> --- a/gdb/aarch64-linux-nat.c
>> +++ b/gdb/aarch64-linux-nat.c
>> @@ -843,7 +843,7 @@ aarch64_linux_nat_target::stopped_data_address (CORE_ADDR *addr_p)
>>        kernel can potentially be tagged addresses.  */
>>     struct gdbarch *gdbarch = thread_architecture (inferior_ptid);
>>     const CORE_ADDR addr_trap
>> -    = address_significant (gdbarch, (CORE_ADDR) siginfo.si_addr);
>> +    = gdbarch_remove_non_address_bits (gdbarch, (CORE_ADDR) siginfo.si_addr);
>>     /* Check if the address matches any watched address.  */
>>     state = aarch64_get_debug_reg_state (inferior_ptid.pid ());
>> diff --git a/gdb/aarch64-linux-tdep.c b/gdb/aarch64-linux-tdep.c
>> index 453692df2f4..fffeb6f3df7 100644
>> --- a/gdb/aarch64-linux-tdep.c
>> +++ b/gdb/aarch64-linux-tdep.c
>> @@ -1586,7 +1586,7 @@ aarch64_linux_tagged_address_p (struct gdbarch *gdbarch, struct value *address)
>>     CORE_ADDR addr = value_as_address (address);
>>     /* Remove the top byte for the memory range check.  */
>> -  addr = address_significant (gdbarch, addr);
>> +  addr = gdbarch_remove_non_address_bits (gdbarch, addr);
>>     /* Check if the page that contains ADDRESS is mapped with PROT_MTE.  */
>>     if (!linux_address_in_memtag_page (addr))
>> @@ -1612,7 +1612,7 @@ aarch64_linux_memtag_matches_p (struct gdbarch *gdbarch,
>>     /* Fetch the allocation tag for ADDRESS.  */
>>     gdb::optional<CORE_ADDR> atag
>> -    = aarch64_mte_get_atag (address_significant (gdbarch, addr));
>> +    = aarch64_mte_get_atag (gdbarch_remove_non_address_bits (gdbarch, addr));
>>     if (!atag.has_value ())
>>       return true;
>> @@ -1651,7 +1651,7 @@ aarch64_linux_set_memtags (struct gdbarch *gdbarch, struct value *address,
>>     else
>>       {
>>         /* Remove the top byte.  */
>> -      addr = address_significant (gdbarch, addr);
>> +      addr = gdbarch_remove_non_address_bits (gdbarch, addr);
>>         /* Make sure we are dealing with a tagged address to begin with.  */
>>         if (!aarch64_linux_tagged_address_p (gdbarch, address))
>> @@ -1708,7 +1708,7 @@ aarch64_linux_get_memtag (struct gdbarch *gdbarch, struct value *address,
>>       return nullptr;
>>         /* Remove the top byte.  */
>> -      addr = address_significant (gdbarch, addr);
>> +      addr = gdbarch_remove_non_address_bits (gdbarch, addr);
>>         gdb::optional<CORE_ADDR> atag = aarch64_mte_get_atag (addr);
>>         if (!atag.has_value ())
>> @@ -1782,7 +1782,8 @@ aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
>>         uiout->text ("\n");
>>         gdb::optional<CORE_ADDR> atag
>> -    = aarch64_mte_get_atag (address_significant (gdbarch, fault_addr));
>> +    = aarch64_mte_get_atag (gdbarch_remove_non_address_bits (gdbarch,
>> +                                 fault_addr));
>>         gdb_byte ltag = aarch64_mte_get_ltag (fault_addr);
>>         if (!atag.has_value ())
>> @@ -1803,6 +1804,49 @@ aarch64_linux_report_signal_info (struct gdbarch *gdbarch,
>>       }
>>   }
>> +/* AArch64 implementation of the remove_non_address_bits gdbarch hook.  Remove
>> +   non address bits from a pointer value.  */
>> +
>> +static CORE_ADDR
>> +aarch64_remove_non_address_bits (struct gdbarch *gdbarch, CORE_ADDR pointer)
>> +{
>> +  aarch64_gdbarch_tdep *tdep
>> +    = (aarch64_gdbarch_tdep *) gdbarch_tdep (gdbarch);
>> +
>> +  /* By default, we assume TBI and discard the top 8 bits plus the VA range
>> +     select bit (55).  */
>> +  CORE_ADDR mask = (((CORE_ADDR) 1) << (64 - 9)) - 1;
>> +  mask = ~mask;
>> +
>> +  if (tdep->has_pauth ())
>> +    {
>> +      /* Fetch the PAC masks.  These masks are per-process, so we can just
>> +     fetch data from whatever thread we have at the moment.
>> +
>> +     Also, we have both a code mask and a data mask.  For now they are the
>> +     same, but this may change in the future.  */
>> +      struct regcache *regs = get_current_regcache ();
>> +      CORE_ADDR cmask, dmask;
>> +
>> +      if (regs->cooked_read (tdep->pauth_reg_base, &dmask) != REG_VALID)
>> +    dmask = mask;
>> +
>> +      if (regs->cooked_read (tdep->pauth_reg_base + 1, &cmask) != REG_VALID)
>> +    cmask = mask;
>> +
>> +      if (dmask != cmask)
>> +    {
>> +      /* Warn if the masks are different.  */
>> +      warning (_("C mask and D mask differ"));
>> +      mask |= dmask > cmask? dmask : cmask;
>> +    }
>> +      else
>> +    mask |= cmask;
>> +    }
>> +
>> +  return aarch64_remove_top_bits (pointer, mask);
>> +}
>> +
>>   static void
>>   aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
>>   {
>> @@ -1858,7 +1902,8 @@ aarch64_linux_init_abi (struct gdbarch_info info, struct gdbarch *gdbarch)
>>     /* The top byte of a user space address known as the "tag",
>>        is ignored by the kernel and can be regarded as additional
>>        data associated with the address.  */
>> -  set_gdbarch_significant_addr_bit (gdbarch, 56);
>> +  set_gdbarch_remove_non_address_bits (gdbarch,
>> +                       aarch64_remove_non_address_bits);
>>     /* MTE-specific settings and hooks.  */
>>     if (tdep->has_mte ())
>> diff --git a/gdb/arch-utils.c b/gdb/arch-utils.c
>> index ff946ee3767..db77dc44c74 100644
>> --- a/gdb/arch-utils.c
>> +++ b/gdb/arch-utils.c
>> @@ -82,6 +82,14 @@ legacy_register_sim_regno (struct gdbarch *gdbarch, int regnum)
>>       return LEGACY_SIM_REGNO_IGNORE;
>>   }
>> +/* See arch-utils.h */
>> +
>> +CORE_ADDR
>> +default_remove_non_address_bits (struct gdbarch *gdbarch, CORE_ADDR pointer)
>> +{
>> +  /* By default, just return the pointer value.  */
>> +  return pointer;
>> +}
>>   /* See arch-utils.h */
>> diff --git a/gdb/arch-utils.h b/gdb/arch-utils.h
>> index f850e5fd6e7..e117599b171 100644
>> --- a/gdb/arch-utils.h
>> +++ b/gdb/arch-utils.h
>> @@ -132,6 +132,10 @@ extern const struct floatformat **
>>     default_floatformat_for_type (struct gdbarch *gdbarch,
>>                   const char *name, int len);
>> +/* Default implementation of gdbarch_remove_non_address_bits.  */
>> +CORE_ADDR default_remove_non_address_bits (struct gdbarch *gdbarch,
>> +                       CORE_ADDR pointer);
>> +
>>   /* Default implementation of gdbarch_memtag_to_string.  */
>>   extern std::string default_memtag_to_string (struct gdbarch *gdbarch,
>>                            struct value *tag);
>> diff --git a/gdb/arch/aarch64.c b/gdb/arch/aarch64.c
>> index 0f73286f145..120664b5fdf 100644
>> --- a/gdb/arch/aarch64.c
>> +++ b/gdb/arch/aarch64.c
>> @@ -58,3 +58,22 @@ aarch64_create_target_description (const aarch64_features &features)
>>     return tdesc.release ();
>>   }
>> +
>> +/* See arch/aarch64.h.  */
>> +
>> +CORE_ADDR
>> +aarch64_remove_top_bits (CORE_ADDR pointer, CORE_ADDR mask)
>> +{
>> +  /* The VA range select bit is 55.  This bit tells us if we have a
>> +     kernel-space address or a user-space address.  */
>> +  bool kernel_address = (pointer & VA_RANGE_SELECT_BIT_MASK) != 0;
>> +
>> +  /* Remove the top non-address bits.  */
>> +  pointer &= ~mask;
>> +
>> +  /* Sign-extend if we have a kernel-space address.  */
>> +  if (kernel_address)
>> +    pointer |= mask;
>> +
>> +  return pointer;
>> +}
>> diff --git a/gdb/arch/aarch64.h b/gdb/arch/aarch64.h
>> index 8e3fd36726a..f2589666a1e 100644
>> --- a/gdb/arch/aarch64.h
>> +++ b/gdb/arch/aarch64.h
>> @@ -67,6 +67,12 @@ namespace std
>>   target_desc *
>>     aarch64_create_target_description (const aarch64_features &features);
>> +/* Given a pointer value POINTER and a MASK of non-address bits, remove the
>> +   non-address bits from the pointer and sign-extend the result if required.
>> +   The sign-extension is required so we can handle kernel addresses
>> +   correctly.  */
>> +CORE_ADDR aarch64_remove_top_bits (CORE_ADDR pointer, CORE_ADDR mask);
>> +
>>   /* Register numbers of various important registers.
>>      Note that on SVE, the Z registers reuse the V register numbers and the V
>>      registers become pseudo registers.  */
>> @@ -96,6 +102,9 @@ enum aarch64_regnum
>>     AARCH64_LAST_V_ARG_REGNUM = AARCH64_V0_REGNUM + 7
>>   };
>> +/* Bit 55 is used to select between a kernel-space and user-space address.  */
>> +#define VA_RANGE_SELECT_BIT_MASK 0x80000000000000
>> +
>>   #define V_REGISTER_SIZE 16
>>   /* Pseudo register base numbers.  */
>> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
>> index a3be12557f6..c7ccb6c4f0d 100644
>> --- a/gdb/breakpoint.c
>> +++ b/gdb/breakpoint.c
>> @@ -2113,7 +2113,8 @@ update_watchpoint (struct watchpoint *b, int reparse)
>>             loc->gdbarch = value_type (v)->arch ();
>>             loc->pspace = frame_pspace;
>> -          loc->address = address_significant (loc->gdbarch, addr);
>> +          loc->address
>> +            = gdbarch_remove_non_address_bits (loc->gdbarch, addr);
>>             if (bitsize != 0)
>>               {
>> @@ -7136,7 +7137,8 @@ adjust_breakpoint_address (struct gdbarch *gdbarch,
>>         adjusted_bpaddr = gdbarch_adjust_breakpoint_address (gdbarch, bpaddr);
>>       }
>> -      adjusted_bpaddr = address_significant (gdbarch, adjusted_bpaddr);
>> +      adjusted_bpaddr
>> +    = gdbarch_remove_non_address_bits (gdbarch, adjusted_bpaddr);
>>         /* An adjusted breakpoint address can significantly alter
>>        a user's expectations.  Print a warning if an adjustment
>> diff --git a/gdb/gdbarch-components.py b/gdb/gdbarch-components.py
>> index fc10e8600ba..c6836b63c50 100644
>> --- a/gdb/gdbarch-components.py
>> +++ b/gdb/gdbarch-components.py
>> @@ -1116,15 +1116,21 @@ possible it should be in TARGET_READ_PC instead).
>>       invalid=False,
>>   )
>> -Value(
>> +Method(
>>       comment="""
>> -On some machines, not all bits of an address word are significant.
>> -For example, on AArch64, the top bits of an address known as the "tag"
>> -are ignored by the kernel, the hardware, etc. and can be regarded as
>> -additional data associated with the address.
>> +On some architectures, not all bits of a pointer are significant.
>> +On AArch64, for example, the top bits of a pointer may carry a "tag", which
>> +can be ignored by the kernel and the hardware. The "tag" can be regarded as
>> +additional data associated with the pointer, but it is not part of the address.
>> +
>> +Given a pointer for the architecture, this hook removes all the
>> +non-significant bits and sign-extends things as needed. It is used mostly
>> +for data pointers, as opposed to code pointers.
>>   """,
>> -    type="int",
>> -    name="significant_addr_bit",
>> +    type="CORE_ADDR",
>> +    name="remove_non_address_bits",
>> +    params=[("CORE_ADDR", "pointer")],
>> +    predefault="default_remove_non_address_bits",
>>       invalid=False,
>>   )
>> diff --git a/gdb/gdbarch-gen.h b/gdb/gdbarch-gen.h
>> index ddcb4c55615..64930f7f239 100644
>> --- a/gdb/gdbarch-gen.h
>> +++ b/gdb/gdbarch-gen.h
>> @@ -609,13 +609,18 @@ typedef CORE_ADDR (gdbarch_addr_bits_remove_ftype) (struct gdbarch *gdbarch, COR
>>   extern CORE_ADDR gdbarch_addr_bits_remove (struct gdbarch *gdbarch, CORE_ADDR addr);
>>   extern void set_gdbarch_addr_bits_remove (struct gdbarch *gdbarch, gdbarch_addr_bits_remove_ftype *addr_bits_remove);
>> -/* On some machines, not all bits of an address word are significant.
>> -   For example, on AArch64, the top bits of an address known as the "tag"
>> -   are ignored by the kernel, the hardware, etc. and can be regarded as
>> -   additional data associated with the address. */
>> -
>> -extern int gdbarch_significant_addr_bit (struct gdbarch *gdbarch);
>> -extern void set_gdbarch_significant_addr_bit (struct gdbarch *gdbarch, int significant_addr_bit);
>> +/* On some architectures, not all bits of a pointer are significant.
>> +   On AArch64, for example, the top bits of a pointer may carry a "tag", which
>> +   can be ignored by the kernel and the hardware. The "tag" can be regarded as
>> +   additional data associated with the pointer, but it is not part of the address.
>> +
>> +   Given a pointer for the architecture, this hook removes all the
>> +   non-significant bits and sign-extends things as needed. It is used mostly
>> +   for data pointers, as opposed to code pointers. */
>> +
>> +typedef CORE_ADDR (gdbarch_remove_non_address_bits_ftype) (struct gdbarch *gdbarch, CORE_ADDR pointer);
>> +extern CORE_ADDR gdbarch_remove_non_address_bits (struct gdbarch *gdbarch, CORE_ADDR pointer);
>> +extern void set_gdbarch_remove_non_address_bits (struct gdbarch *gdbarch, gdbarch_remove_non_address_bits_ftype *remove_non_address_bits);
>>   /* Return a string representation of the memory tag TAG. */
>> diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c
>> index 68ef0480219..d536d8578af 100644
>> --- a/gdb/gdbarch.c
>> +++ b/gdb/gdbarch.c
>> @@ -140,7 +140,7 @@ struct gdbarch
>>     int frame_red_zone_size;
>>     gdbarch_convert_from_func_ptr_addr_ftype *convert_from_func_ptr_addr;
>>     gdbarch_addr_bits_remove_ftype *addr_bits_remove;
>> -  int significant_addr_bit;
>> +  gdbarch_remove_non_address_bits_ftype *remove_non_address_bits;
>>     gdbarch_memtag_to_string_ftype *memtag_to_string;
>>     gdbarch_tagged_address_p_ftype *tagged_address_p;
>>     gdbarch_memtag_matches_p_ftype *memtag_matches_p;
>> @@ -327,6 +327,7 @@ gdbarch_alloc (const struct gdbarch_info *info,
>>     gdbarch->stabs_argument_has_addr = default_stabs_argument_has_addr;
>>     gdbarch->convert_from_func_ptr_addr = convert_from_func_ptr_addr_identity;
>>     gdbarch->addr_bits_remove = core_addr_identity;
>> +  gdbarch->remove_non_address_bits = default_remove_non_address_bits;
>>     gdbarch->memtag_to_string = default_memtag_to_string;
>>     gdbarch->tagged_address_p = default_tagged_address_p;
>>     gdbarch->memtag_matches_p = default_memtag_matches_p;
>> @@ -496,7 +497,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
>>     /* Skip verify of frame_red_zone_size, invalid_p == 0 */
>>     /* Skip verify of convert_from_func_ptr_addr, invalid_p == 0 */
>>     /* Skip verify of addr_bits_remove, invalid_p == 0 */
>> -  /* Skip verify of significant_addr_bit, invalid_p == 0 */
>> +  /* Skip verify of remove_non_address_bits, invalid_p == 0 */
>>     /* Skip verify of memtag_to_string, invalid_p == 0 */
>>     /* Skip verify of tagged_address_p, invalid_p == 0 */
>>     /* Skip verify of memtag_matches_p, invalid_p == 0 */
>> @@ -974,8 +975,8 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
>>                         "gdbarch_dump: addr_bits_remove = <%s>\n",
>>                         host_address_to_string (gdbarch->addr_bits_remove));
>>     gdb_printf (file,
>> -                      "gdbarch_dump: significant_addr_bit = %s\n",
>> -                      plongest (gdbarch->significant_addr_bit));
>> +                      "gdbarch_dump: remove_non_address_bits = <%s>\n",
>> +                      host_address_to_string (gdbarch->remove_non_address_bits));
>>     gdb_printf (file,
>>                         "gdbarch_dump: memtag_to_string = <%s>\n",
>>                         host_address_to_string (gdbarch->memtag_to_string));
>> @@ -3147,21 +3148,21 @@ set_gdbarch_addr_bits_remove (struct gdbarch *gdbarch,
>>     gdbarch->addr_bits_remove = addr_bits_remove;
>>   }
>> -int
>> -gdbarch_significant_addr_bit (struct gdbarch *gdbarch)
>> +CORE_ADDR
>> +gdbarch_remove_non_address_bits (struct gdbarch *gdbarch, CORE_ADDR pointer)
>>   {
>>     gdb_assert (gdbarch != NULL);
>> -  /* Skip verify of significant_addr_bit, invalid_p == 0 */
>> +  gdb_assert (gdbarch->remove_non_address_bits != NULL);
>>     if (gdbarch_debug >= 2)
>> -    gdb_printf (gdb_stdlog, "gdbarch_significant_addr_bit called\n");
>> -  return gdbarch->significant_addr_bit;
>> +    gdb_printf (gdb_stdlog, "gdbarch_remove_non_address_bits called\n");
>> +  return gdbarch->remove_non_address_bits (gdbarch, pointer);
>>   }
>>   void
>> -set_gdbarch_significant_addr_bit (struct gdbarch *gdbarch,
>> -                                  int significant_addr_bit)
>> +set_gdbarch_remove_non_address_bits (struct gdbarch *gdbarch,
>> +                                     gdbarch_remove_non_address_bits_ftype remove_non_address_bits)
>>   {
>> -  gdbarch->significant_addr_bit = significant_addr_bit;
>> +  gdbarch->remove_non_address_bits = remove_non_address_bits;
>>   }
>>   std::string
>> diff --git a/gdb/target.c b/gdb/target.c
>> index 18e53aa5d27..4ce1b9451a0 100644
>> --- a/gdb/target.c
>> +++ b/gdb/target.c
>> @@ -1644,7 +1644,7 @@ memory_xfer_partial (struct target_ops *ops, enum target_object object,
>>     if (len == 0)
>>       return TARGET_XFER_EOF;
>> -  memaddr = address_significant (target_gdbarch (), memaddr);
>> +  memaddr = gdbarch_remove_non_address_bits (target_gdbarch (), memaddr);
>>     /* Fill in READBUF with breakpoint shadows, or WRITEBUF with
>>        breakpoint insns, thus hiding out from higher layers whether
>> diff --git a/gdb/testsuite/gdb.arch/aarch64-non-address-bits.c b/gdb/testsuite/gdb.arch/aarch64-non-address-bits.c
>> new file mode 100644
>> index 00000000000..3cf6d63da17
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.arch/aarch64-non-address-bits.c
>> @@ -0,0 +1,25 @@
>> +/* This file is part of GDB, the GNU debugger.
>> +
>> +   Copyright 2022 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/>.  */
>> +
>> +static long l = 0;
>> +static long *l_ptr = &l;
>> +
>> +int
>> +main (int argc, char **argv)
>> +{
>> +  return *l_ptr;
>> +}
>> diff --git a/gdb/testsuite/gdb.arch/aarch64-non-address-bits.exp b/gdb/testsuite/gdb.arch/aarch64-non-address-bits.exp
>> new file mode 100644
>> index 00000000000..2b5a7b2f517
>> --- /dev/null
>> +++ b/gdb/testsuite/gdb.arch/aarch64-non-address-bits.exp
>> @@ -0,0 +1,121 @@
>> +# Copyright 2022 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/>.
>> +#
>> +# This file is part of the gdb testsuite.
>> +#
>> +# Test that GDB for AArch64/Linux can properly handle pointers with
>> +# the upper 16 bits (PAC) or 8 bits (Tag) set, as well as the
>> +# VA_RANGE_SELECT bit (55).
>> +
>> +if {![is_aarch64_target]} {
>> +    verbose "Skipping ${gdb_test_file_name}."
>> +    return
>> +}
>> +
>> +global hex
>> +global decimal
>> +
>> +standard_testfile
>> +if { [prepare_for_testing "failed to prepare" ${testfile} ${srcfile}] } {
>> +    return -1
>> +}
>> +
>> +if ![runto_main] {
>> +    return -1
>> +}
>> +
>> +# We need to iterate over two distinct ranges, separated by a single bit.
>> +# This bit is 55 (VA_RANGE_SELECT) which tells us if we have a kernel-space
>> +# address or a user-space address.
>> +
>> +# The tag field has 8 bits.
>> +set tag_bits_count 8
>> +
>> +# The pac field has 7 bits.
>> +set pac_bits_count 7
>> +
>> +# A couple patterns that we reuse for the tests later.  One is for a successful
>> +# memory read and the other is for a memory read failure.
>> +set memory_read_ok_pattern "$hex\( <l>\)?:\[ \t\]+$hex"
>> +set memory_read_fail_pattern "$hex:\[ \t\]+Cannot access memory at address $hex"
>> +
>> +set pac_enabled 0
>> +
>> +# Check if PAC is enabled.
>> +gdb_test_multiple "ptype \$pauth_cmask" "fetch PAC cmask" {
>> +    -re "type = long\r\n$gdb_prompt" {
>> +    set pac_enabled 1
>> +    }
>> +    -re "type = void\r\n$gdb_prompt" {
>> +    }
>> +    -re ".*$gdb_prompt $" {
>> +    fail $gdb_test_name
>> +    return 1
>> +    }
>> +}
>> +
>> +# Value of the cmask register.
>> +set cmask 0
>> +
>> +# If there are PAC registers, GDB uses those to unmask the PAC bits.
>> +if {$pac_enabled} {
>> +    set cmask [get_valueof "" "\$pauth_cmask >> 48" "0" "fetch PAC cmask"]
>> +}
>> +
>> +# Cycle through the tag and pac bit ranges and check how GDB
>> +# behaves when trying to access these addresses.
>> +foreach upper_bits {"0x0" "0x1" "0x2" "0x4" "0x8" "0x10" "0x20" "0x40" "0x80"} {
>> +    foreach lower_bits {"0x0" "0x1" "0x2" "0x4" "0x8" "0x10" "0x20" "0x40"} {
>> +
>> +    # A successful memory read pattern
>> +    set pattern $memory_read_ok_pattern
>> +
>> +    if {!$pac_enabled} {
>> +        # If PAC is not supported, memory reads will fail if
>> +        # lower_bits != 0x0
>> +        if {$lower_bits != "0x0"} {
>> +        set pattern $memory_read_fail_pattern
>> +        }
>> +    } else {
>> +        # Otherwise, figure out if the memory read will succeed or not by
>> +        # checking cmask.
>> +        gdb_test_multiple "p/x (~${cmask}ULL & (${lower_bits}ULL))" "" {
>> +        -re "= 0x0\r\n$gdb_prompt" {
>> +            # Either cmask is 0x7F or lower_bits is 0x0. Either way, the
>> +            # memory read should succeed.
>> +        }
>> +        -re "= $hex\r\n$gdb_prompt" {
>> +            if {$lower_bits != "0x0"} {
>> +            # cmask doesn't mask off all the PAC bits, which
>> +            # results in a memory read failure, with the actual
>> +            # address being accessed differing from the one we
>> +            # passed.
>> +            set pattern $memory_read_fail_pattern
>> +            }
>> +        }
>> +        }
>> +    }
>> +
>> +    # Test without the VA_RANGE_SELECT bit set.
>> +    gdb_test "x/gx ((unsigned long) l_ptr | ((${upper_bits}ULL << 56) | (${lower_bits}ULL << 48)))" \
>> +        $pattern \
>> +        "user-space memory access tag bits $upper_bits and pac bits $lower_bits"
>> +
>> +    # Now test with the VA_RANGE_SELECT bit set.
>> +    gdb_test "x/gx ((unsigned long) l_ptr | ((${upper_bits}ULL << 56) | (${lower_bits}ULL << 48) | (1ULL << 55))) " \
>> +        $memory_read_fail_pattern \
>> +        "kernel-space memory access tag bits $upper_bits and pac bits $lower_bits"
>> +    }
>> +}
>> diff --git a/gdb/utils.c b/gdb/utils.c
>> index 413a4f4d53b..f88d669c016 100644
>> --- a/gdb/utils.c
>> +++ b/gdb/utils.c
>> @@ -3139,28 +3139,6 @@ show_debug_timestamp (struct ui_file *file, int from_tty,
>>   }
>>   \f
>> -/* See utils.h.  */
>> -
>> -CORE_ADDR
>> -address_significant (gdbarch *gdbarch, CORE_ADDR addr)
>> -{
>> -  /* Clear insignificant bits of a target address and sign extend resulting
>> -     address, avoiding shifts larger or equal than the width of a CORE_ADDR.
>> -     The local variable ADDR_BIT stops the compiler reporting a shift overflow
>> -     when it won't occur.  Skip updating of target address if current target
>> -     has not set gdbarch significant_addr_bit.  */
>> -  int addr_bit = gdbarch_significant_addr_bit (gdbarch);
>> -
>> -  if (addr_bit && (addr_bit < (sizeof (CORE_ADDR) * HOST_CHAR_BIT)))
>> -    {
>> -      CORE_ADDR sign = (CORE_ADDR) 1 << (addr_bit - 1);
>> -      addr &= ((CORE_ADDR) 1 << addr_bit) - 1;
>> -      addr = (addr ^ sign) - sign;
>> -    }
>> -
>> -  return addr;
>> -}
>> -
>>   const char *
>>   paddress (struct gdbarch *gdbarch, CORE_ADDR addr)
>>   {
>> diff --git a/gdb/utils.h b/gdb/utils.h
>> index d2acf899ba2..237ef0a5d99 100644
>> --- a/gdb/utils.h
>> +++ b/gdb/utils.h
>> @@ -278,9 +278,6 @@ extern void fputs_styled (const char *linebuffer,
>>   extern void fputs_highlighted (const char *str, const compiled_regex &highlight,
>>                      struct ui_file *stream);
>> -/* Return the address only having significant bits.  */
>> -extern CORE_ADDR address_significant (gdbarch *gdbarch, CORE_ADDR addr);
>> -
>>   /* Convert CORE_ADDR to string in platform-specific manner.
>>      This is usually formatted similar to 0x%lx.  */
>>   extern const char *paddress (struct gdbarch *gdbarch, CORE_ADDR addr);
>> diff --git a/gdbserver/linux-aarch64-low.cc b/gdbserver/linux-aarch64-low.cc
>> index db508696261..8a6077b6c76 100644
>> --- a/gdbserver/linux-aarch64-low.cc
>> +++ b/gdbserver/linux-aarch64-low.cc
>> @@ -508,21 +508,37 @@ aarch64_target::low_remove_point (raw_bkpt_type type, CORE_ADDR addr,
>>     return ret;
>>   }
>> -/* Return the address only having significant bits.  This is used to ignore
>> -   the top byte (TBI).  */
>> -
>>   static CORE_ADDR
>> -address_significant (CORE_ADDR addr)
>> +aarch64_remove_non_address_bits (CORE_ADDR pointer)
>>   {
>> -  /* Clear insignificant bits of a target address and sign extend resulting
>> -     address.  */
>> -  int addr_bit = 56;
>> +  /* By default, we assume TBI and discard the top 8 bits plus the
>> +     VA range select bit (55).  */
>> +  CORE_ADDR mask = (((CORE_ADDR) 1) << (64 - 9)) - 1;
>> +  mask = ~mask;
>> +
>> +  /* Check if PAC is available for this target.  */
>> +  if (tdesc_contains_feature (current_process ()->tdesc,
>> +                  "org.gnu.gdb.aarch64.pauth"))
>> +    {
>> +      /* Fetch the PAC masks.  These masks are per-process, so we can just
>> +     fetch data from whatever thread we have at the moment.
>> +
>> +     Also, we have both a code mask and a data mask.  For now they are the
>> +     same, but this may change in the future.  */
>> -  CORE_ADDR sign = (CORE_ADDR) 1 << (addr_bit - 1);
>> -  addr &= ((CORE_ADDR) 1 << addr_bit) - 1;
>> -  addr = (addr ^ sign) - sign;
>> +      struct regcache *regs = get_thread_regcache (current_thread, 1);
>> +      CORE_ADDR dmask = regcache_raw_get_unsigned_by_name (regs, "pauth_dmask");
>> +      CORE_ADDR cmask = regcache_raw_get_unsigned_by_name (regs, "pauth_cmask");
>> +
>> +      if (dmask != cmask && dmask != 0 && cmask != 0)
>> +    {
>> +      /* Warn if the masks are different.  */
>> +      warning (_("C mask and D mask differ"));
>> +      mask |= (dmask > cmask)? dmask : cmask;
>> +    }
>> +    }
>> -  return addr;
>> +  return aarch64_remove_top_bits (pointer, mask);
>>   }
>>   /* Implementation of linux target ops method "low_stopped_data_address".  */
>> @@ -549,7 +565,7 @@ aarch64_target::low_stopped_data_address ()
>>        hardware watchpoint hit.  The stopped data addresses coming from the
>>        kernel can potentially be tagged addresses.  */
>>     const CORE_ADDR addr_trap
>> -    = address_significant ((CORE_ADDR) siginfo.si_addr);
>> +    = aarch64_remove_non_address_bits ((CORE_ADDR) siginfo.si_addr);
>>     /* Check if the address matches any watched address.  */
>>     state = aarch64_get_debug_reg_state (pid_of (current_thread));
>