[PATCH v3] Return the regnum for PC (32) on aarch64

[Yichao Yu]

Sorry for the duplicated post.... I think somehow the university
network prevented the email from going out earlier today...

On Tue, May 17, 2022 at 8:45 PM Yichao Yu <yyc1992@gmail.com> wrote:
>
> This will allow the unwind info to explicitly specify a different value
> for the return address from the link register.
> Such usage, although uncommon, is valid and useful for signal frames.
> It is also supported by aadwarf64 from ARM (Note 9 in [1]).
>
> Ref https://sourceware.org/pipermail/gdb/2022-May/050091.html
>
> [1] https://github.com/ARM-software/abi-aa/blob/2022Q1/aadwarf64/aadwarf64.rst#dwarf-register-names
> ---
>  gdb/aarch64-tdep.c                           |  3 +
>  gdb/aarch64-tdep.h                           |  1 +
>  gdb/testsuite/gdb.arch/aarch64-unwind-pc.S   | 48 ++++++++++++++
>  gdb/testsuite/gdb.arch/aarch64-unwind-pc.exp | 70 ++++++++++++++++++++
>  4 files changed, 122 insertions(+)
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-unwind-pc.S
>  create mode 100644 gdb/testsuite/gdb.arch/aarch64-unwind-pc.exp
>
> diff --git a/gdb/aarch64-tdep.c b/gdb/aarch64-tdep.c
> index 9d06ebfe27c..f9eb455232f 100644
> --- a/gdb/aarch64-tdep.c
> +++ b/gdb/aarch64-tdep.c
> @@ -2219,6 +2219,9 @@ aarch64_dwarf_reg_to_regnum (struct gdbarch *gdbarch, int reg)
>    if (reg == AARCH64_DWARF_SP)
>      return AARCH64_SP_REGNUM;
>
> +  if (reg == AARCH64_DWARF_PC)
> +    return AARCH64_PC_REGNUM;
> +
>    if (reg >= AARCH64_DWARF_V0 && reg <= AARCH64_DWARF_V0 + 31)
>      return AARCH64_V0_REGNUM + reg - AARCH64_DWARF_V0;
>
> diff --git a/gdb/aarch64-tdep.h b/gdb/aarch64-tdep.h
> index e4cdebb6311..aa1bedbdac6 100644
> --- a/gdb/aarch64-tdep.h
> +++ b/gdb/aarch64-tdep.h
> @@ -34,6 +34,7 @@ struct regset;
>  /* AArch64 Dwarf register numbering.  */
>  #define AARCH64_DWARF_X0   0
>  #define AARCH64_DWARF_SP  31
> +#define AARCH64_DWARF_PC  32
>  #define AARCH64_DWARF_PAUTH_RA_STATE  34
>  #define AARCH64_DWARF_PAUTH_DMASK  35
>  #define AARCH64_DWARF_PAUTH_CMASK  36
> diff --git a/gdb/testsuite/gdb.arch/aarch64-unwind-pc.S b/gdb/testsuite/gdb.arch/aarch64-unwind-pc.S
> new file mode 100644
> index 00000000000..6cc4f80e349
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-unwind-pc.S
> @@ -0,0 +1,48 @@
> +/* Copyright 2022 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/>.  */
> +
> +        .text
> +        .globl main
> +        .type main,#function
> +main:
> +        .cfi_startproc
> +        stp     x29, x30, [sp, -16]!
> +        .cfi_def_cfa sp, 16
> +        .cfi_offset x29, 0
> +        .cfi_offset x30, 8
> +        bl test_func
> +        ldp     x29, x30, [sp], 16
> +        .cfi_restore x29
> +        .cfi_restore x30
> +        .cfi_def_cfa sp, 0
> +        mov     x0, 0
> +        ret
> +        .cfi_endproc
> +
> +        .globl test_func
> +test_func:
> +        .cfi_startproc
> +        // Unwind x30 to a different value
> +        // CFA_val_expression x30 const2u 0x1234
> +        .cfi_escape 0x16, 30, 0x03, 0x0a, 0x34, 0x12
> +        // CFA_val_expression pc breg30 0
> +        .cfi_escape 0x16, 32, 0x02, 0x8e, 0x00
> +        mov     x0, x30
> +        .cfi_register 32, x0
> +        mov     x30, 0x1234
> +        ret     x0
> +        .cfi_endproc
> diff --git a/gdb/testsuite/gdb.arch/aarch64-unwind-pc.exp b/gdb/testsuite/gdb.arch/aarch64-unwind-pc.exp
> new file mode 100644
> index 00000000000..105b9a9cc3a
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/aarch64-unwind-pc.exp
> @@ -0,0 +1,70 @@
> +# 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 explicitly unwinding the PC DWARF register on aarch64
> +
> +if {![is_aarch64_target]} then {
> +    verbose "Skipping ${gdb_test_file_name}."
> +    return
> +}
> +
> +standard_testfile .S
> +
> +if { [prepare_for_testing "failed to prepare" $testfile $srcfile] } {
> +    return -1
> +}
> +
> +if ![runto_main] {
> +    return -1
> +}
> +
> +proc test_reg_vals {} {
> +    gdb_test "p \$pc - &main" "= 8" "p \$pc"
> +    gdb_test "p/x \$x30" "= 0x1234" "p \$x30"
> +}
> +
> +proc test_unwind_pc { inst } {
> +    gdb_test "si" "$inst" "single step"
> +    gdb_test "backtrace" \
> +       ".*#1.*in main ().*" \
> +       "backtrace"
> +    gdb_test "up" "in main ().*" "parent frame"
> +    test_reg_vals
> +}
> +
> +# Ready to enter the function
> +gdb_test "si" "bl test_func" "call site"
> +# Step through the 3 instructions in the function to make sure that
> +# we have the same unwind info throughout.
> +with_test_prefix "1st stepi" {
> +    test_unwind_pc "mov     x0, x30"
> +}
> +with_test_prefix "2nd stepi" {
> +    test_unwind_pc "mov     x30, 0x1234"
> +}
> +with_test_prefix "3rd stepi" {
> +    test_unwind_pc "ret     x0"
> +}
> +# Check again after we returned
> +with_test_prefix "final" {
> +    # Check that we've stepped out (si prints out the new function name)
> +    gdb_test "si" ".*main *().*" "single step out"
> +    gdb_test "backtrace" \
> +       "#0\[\t \]+main ().*" \
> +       "backtrace"
> +    test_reg_vals
> +}
> --
> 2.36.1
>