Re: [PATCHv4] aarch64: detect atomic sequences like other ll/sc architectures

[Andrew Pinski <pinskia@gmail.com>]

On Thu, Apr 24, 2014 at 11:35 AM, Kyle McMartin <kmcmarti@redhat.com> wrote:
> Once more with feeling. :-) Fixed ChangeLog entries and whitespace.
>
> 2014-04-24  Kyle McMartin  <kyle@redhat.com>
>
> gdb:
>         * aarch64-tdep.c (aarch64_software_single_step): New function.
>         (aarch64_gdbarch_init): Handle single stepping of atomic sequences
>         with aarch64_software_single_step.
>
> gdb/testsuite:
>         * gdb.arch/aarch64-atomic-inst.c: New file.
>         * gdb.arch/aarch64-atomic-inst.exp: New file.
>
> ---
>  gdb/aarch64-tdep.c                             | 77 ++++++++++++++++++++++++++
>  gdb/testsuite/gdb.arch/aarch64-atomic-inst.c   | 48 ++++++++++++++++
>  gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp | 48 ++++++++++++++++
>  3 files changed, 173 insertions(+)
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-atomic-inst.c
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp
>
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index bba10d8..b64bbde 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -2509,6 +2509,82 @@ value_of_aarch64_user_reg (struct frame_info *frame, const void *baton)
>  }
>
>
> +/* Implement the "software_single_step" gdbarch method, needed to
> +   single step through atomic sequences on AArch64.  */
> +
> +static int
> +aarch64_software_single_step (struct frame_info *frame)
> +{
> +  struct gdbarch *gdbarch = get_frame_arch (frame);
> +  struct address_space *aspace = get_frame_address_space (frame);
> +  enum bfd_endian byte_order = gdbarch_byte_order (gdbarch);
> +  const int insn_size = 4;
> +  const int atomic_sequence_length = 16; /* Instruction sequence length.  */
> +  CORE_ADDR pc = get_frame_pc (frame);
> +  CORE_ADDR breaks[2] = { -1, -1 };
> +  CORE_ADDR loc = pc;
> +  CORE_ADDR closing_insn = 0;
> +  uint32_t insn = read_memory_unsigned_integer (loc, insn_size, byte_order);


I think this is broken for big-endian aarch64.  Instructions are
always in little-endian mode so we really should be reading them
always as little-endian.


Thanks,
Andrew Pinski

> +  int index;
> +  int insn_count;
> +  int bc_insn_count = 0; /* Conditional branch instruction count.  */
> +  int last_breakpoint = 0; /* Defaults to 0 (no breakpoints placed).  */
> +
> +  /* Look for a Load Exclusive instruction which begins the sequence.  */
> +  if (!decode_masked_match (insn, 0x3fc00000, 0x08400000))
> +    return 0;
> +
> +  for (insn_count = 0; insn_count < atomic_sequence_length; ++insn_count)
> +    {
> +      int32_t offset;
> +      unsigned cond;
> +
> +      loc += insn_size;
> +      insn = read_memory_unsigned_integer (loc, insn_size, byte_order);
> +
> +      /* Check if the instruction is a conditional branch.  */
> +      if (decode_bcond (loc, insn, &cond, &offset))
> +       {
> +         if (bc_insn_count >= 1)
> +           return 0;
> +
> +         /* It is, so we'll try to set a breakpoint at the destination.  */
> +         breaks[1] = loc + offset;
> +
> +         bc_insn_count++;
> +         last_breakpoint++;
> +       }
> +
> +      /* Look for the Store Exclusive which closes the atomic sequence.  */
> +      if (decode_masked_match (insn, 0x3fc00000, 0x08000000))
> +       {
> +         closing_insn = loc;
> +         break;
> +       }
> +    }
> +
> +  /* We didn't find a closing Store Exclusive instruction, fall back.  */
> +  if (!closing_insn)
> +    return 0;
> +
> +  /* Insert breakpoint after the end of the atomic sequence.  */
> +  breaks[0] = loc + insn_size;
> +
> +  /* Check for duplicated breakpoints, and also check that the second
> +     breakpoint is not within the atomic sequence.  */
> +  if (last_breakpoint
> +      && (breaks[1] == breaks[0]
> +         || (breaks[1] >= pc && breaks[1] <= closing_insn)))
> +    last_breakpoint = 0;
> +
> +  /* Insert the breakpoint at the end of the sequence, and one at the
> +     destination of the conditional branch, if it exists.  */
> +  for (index = 0; index <= last_breakpoint; index++)
> +    insert_single_step_breakpoint (gdbarch, aspace, breaks[index]);
> +
> +  return 1;
> +}
> +
>  /* Initialize the current architecture based on INFO.  If possible,
>     re-use an architecture from ARCHES, which is a list of
>     architectures already created during this debugging session.
> @@ -2624,6 +2700,7 @@ aarch64_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
>    set_gdbarch_breakpoint_from_pc (gdbarch, aarch64_breakpoint_from_pc);
>    set_gdbarch_cannot_step_breakpoint (gdbarch, 1);
>    set_gdbarch_have_nonsteppable_watchpoint (gdbarch, 1);
> +  set_gdbarch_software_single_step (gdbarch, aarch64_software_single_step);
>
>    /* Information about registers, etc.  */
>    set_gdbarch_sp_regnum (gdbarch, AARCH64_SP_REGNUM);
> diff --git a/gdb/testsuite/gdb.arch/aarch64-atomic-inst.c b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.c
> new file mode 100644
> index 0000000..9a73c7a
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.c
> @@ -0,0 +1,48 @@
> +/* This file is part of GDB, the GNU debugger.
> +
> +   Copyright 2008-2014 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/>.  */
> +
> +int main(void)
> +{
> +  unsigned long tmp, cond;
> +  unsigned long dword = 0;
> +
> +  /* Test that we can step over ldxr/stxr. This sequence should step from
> +     ldxr to the following __asm __volatile.  */
> +  __asm __volatile ("1:     ldxr    %0,%2\n"                             \
> +                    "       cmp     %0,#1\n"                             \
> +                    "       b.eq    out\n"                               \
> +                    "       add     %0,%0,1\n"                           \
> +                    "       stxr    %w1,%0,%2\n"                         \
> +                    "       cbnz    %w1,1b"                              \
> +                    : "=&r" (tmp), "=&r" (cond), "+Q" (dword)            \
> +                    : : "memory");
> +
> +  /* This sequence should take the conditional branch and step from ldxr
> +     to the return dword line.  */
> +  __asm __volatile ("1:     ldxr    %0,%2\n"                             \
> +                    "       cmp     %0,#1\n"                             \
> +                    "       b.eq    out\n"                               \
> +                    "       add     %0,%0,1\n"                           \
> +                    "       stxr    %w1,%0,%2\n"                         \
> +                    "       cbnz    %w1,1b\n"                            \
> +                    : "=&r" (tmp), "=&r" (cond), "+Q" (dword)            \
> +                    : : "memory");
> +
> +  dword = -1;
> +__asm __volatile ("out:\n");
> +  return dword;
> +}
> diff --git a/gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp
> new file mode 100644
> index 0000000..377aebc
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-atomic-inst.exp
> @@ -0,0 +1,48 @@
> +# Copyright 2008-2014 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, write to the Free Software
> +# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
> +#
> +# This file is part of the gdb testsuite.
> +
> +# Test single stepping through atomic sequences beginning with
> +# a ldxr instruction and ending with a stxr instruction.
> +
> +if {![istarget "aarch64*"]} {
> +    verbose "Skipping ${gdb_test_file_name}."
> +    return
> +}
> +
> +standard_testfile
> +if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
> +    return -1
> +}
> +
> +if ![runto_main] {
> +    untested "could not run to main"
> +    return -1
> +}
> +
> +gdb_breakpoint "[gdb_get_line_number "ldxr"]" \
> +  "Breakpoint $decimal at $hex" \
> +  "Set the breakpoint at the start of the sequence"
> +
> +gdb_test "continue" "Continuing.*Breakpoint $decimal.*" \
> +  "Continue until breakpoint"
> +
> +gdb_test "next" ".*__asm __volatile.*" \
> +  "Step through the ldxr/stxr sequence"
> +
> +gdb_test "next" ".*return dword.*" \
> +  "Stepped through sequence through conditional branch"
> --
> 1.9.0
>