[PATCH 4/4] Add support for Intel PKRU register to GDB and GDBserver.

[Pedro Alves]

On 05/13/2016 01:50 PM, Michael Sturm wrote:
> This patch adds support for the registers added by the
> Memory Protection Keys for Userspace (PKU aka PKEYs) feature.
> Native and remote debugging are covered by this patch.
> 
> The XSAVE area is extended with a new state containing
> the 32-bit wide PKRU register. The new register is added to
> amd64-avx-mpx_avx512-* tdesc, thus it is renamed accordingly.

Is that really the right thing to do?  What about machines that
_don't_ support pkru?  Shouldn't we keep the older descriptions
for those?

> Also,
> respective xstate mask X86_XSTATE_AVX_MPX_AVX512_MASK is renamed to
> X86_XSTATE_AVX_MPX_AVX512_PKU_MASK to reflect the new feature set
> it supports.

>      (X86_XSTATE_PKRU_SIZE): New makro.
>      (HAS_PKRU(XCR0)): New makro.

"macro".

>      (i386_linux_gregset_reg_offset): Adde PKRU register.

"Add".

> diff --git a/gdb/gdbserver/linux-amd64-ipa.c b/gdb/gdbserver/linux-amd64-ipa.c
> index 40c6995..1851b60 100644
> --- a/gdb/gdbserver/linux-amd64-ipa.c
> +++ b/gdb/gdbserver/linux-amd64-ipa.c
> @@ -185,7 +185,7 @@ get_ipa_tdesc (int idx)
>      case X86_TDESC_AVX_MPX:
>        return tdesc_amd64_avx_mpx_linux;
>      case X86_TDESC_AVX_MPX_AVX512:
> -      return tdesc_amd64_avx_mpx_avx512_linux;
> +      return tdesc_amd64_avx_mpx_avx512_pku_linux;

No rename for X86_TDESC_AVX_MPX_AVX512?

>      case X86_TDESC_AVX_AVX512:
>        return tdesc_amd64_avx_avx512_linux;
>      default:
> @@ -219,6 +219,6 @@ initialize_low_tracepoint (void)
>    init_registers_amd64_avx_linux ();
>    init_registers_amd64_avx_mpx_linux ();
>    init_registers_amd64_mpx_linux ();
> -  init_registers_amd64_avx_mpx_avx512_linux ();
> +  init_registers_amd64_avx_mpx_avx512_pku_linux ();
>    init_registers_amd64_avx_avx512_linux ();
>  }
> diff --git a/gdb/gdbserver/linux-i386-ipa.c b/gdb/gdbserver/linux-i386-ipa.c
> index 5e00a59..5f1e09d 100644
> --- a/gdb/gdbserver/linux-i386-ipa.c
> +++ b/gdb/gdbserver/linux-i386-ipa.c
> @@ -265,7 +265,7 @@ get_ipa_tdesc (int idx)
>      case X86_TDESC_AVX_AVX512:
>        return tdesc_i386_avx_avx512_linux;
>      case X86_TDESC_AVX_MPX_AVX512:

Ditto.

> -      return tdesc_i386_avx_mpx_avx512_linux;
> +      return tdesc_i386_avx_mpx_avx512_pku_linux;
>      default:
>        internal_error (__FILE__, __LINE__,
>  		      "unknown ipa tdesc index: %d", idx);

> diff --git a/gdb/nat/x86-gcc-cpuid.h b/gdb/nat/x86-gcc-cpuid.h
> index 1045521..2283ea3 100644
> --- a/gdb/nat/x86-gcc-cpuid.h
> +++ b/gdb/nat/x86-gcc-cpuid.h
> @@ -84,6 +84,10 @@
>  #define bit_AVX512CD	(1 << 28)
>  #define bit_SHA		(1 << 29)
>  
> +/* %ecx */
> +#define bit_PKU	(1 << 3)
> +#define bit_OSPKE	(1 << 4)
> +

This file is imported from gcc, and the upstream file has more bits in
in.  Please instead submit a separate, preliminary patch that syncs
our copy with upstream's.

> +static inline unsigned long
> +rdpkru(void)

Space before parens.

> +{
> +  unsigned int eax, edx;
> +  unsigned int ecx = 0;
> +  unsigned int pkru;
> +
> +  asm volatile(".byte 0x0f,0x01,0xee\n\t"

Ditto.

> +               : "=a" (eax), "=d" (edx)
> +               : "c" (ecx));
> +  pkru = eax;
> +  return pkru;
> +}
> +
> +static inline void
> +wrpkru(unsigned int pkru)

Ditto.

> +{
> +  unsigned int eax = pkru;
> +  unsigned int ecx = 0;
> +  unsigned int edx = 0;
> +
> +  asm volatile(".byte 0x0f,0x01,0xef\n\t"
> +               : : "a" (eax), "c" (ecx), "d" (edx));

Ditto.


> +}
> +
> +
> +unsigned int NOINLINE
> +have_pkru (void)
> +{
> +  unsigned int eax, ebx, ecx, edx;
> +
> +  if (!__get_cpuid (1, &eax, &ebx, &ecx, &edx))
> +    return 0;
> +
> +  if ((ecx & bit_OSXSAVE) == bit_OSXSAVE)
> +    {
> +      if (__get_cpuid_max (0, NULL) < 7)
> +	return 0;
> +
> +      __cpuid_count (7, 0, eax, ebx, ecx, edx);
> +
> +      if ((ecx & bit_PKU) == bit_PKU)
> +	return 1;
> +      else
> +	return 0;
> +    }
> +  return 0;
> +}
> +
> +int
> +main (int argc, char **argv)
> +{
> +  unsigned int wr_value = 0x12345678;
> +  unsigned int rd_value = 0x0;
> +
> +  if (have_pkru ())
> +    {
> +      wrpkru(wr_value);

Ditto.

> +      asm ("nop\n\t");	/* break here 1.  */
> +
> +      rd_value = rdpkru();

Ditto.

> +      asm ("nop\n\t");	/* break here 2.  */
> +    }
> +  return 0;
> +}
> diff --git a/gdb/testsuite/gdb.arch/i386-pkru.exp b/gdb/testsuite/gdb.arch/i386-pkru.exp
> new file mode 100644
> index 0000000..79d25fb
> --- /dev/null
> +++ b/gdb/testsuite/gdb.arch/i386-pkru.exp
> @@ -0,0 +1,73 @@
> +# Copyright 2015-2016 Free Software Foundation, Inc.
> +#
> +# Contributed by Intel Corp. <michael.sturm@intel.com>
> +#
> +# 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/>.
> +
> +standard_testfile
> +
> +if { ![istarget i?86-*-*] && ![istarget x86_64-*-* ] } {
> +    verbose "Skipping PKEYS tests."
> +    return
> +}
> +
> +set comp_flags "-I${srcdir}/../nat/"
> +
> +if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile} \
> +     [list debug nowarnings additional_flags=${comp_flags}]] } {

Why "nowarnings" ?

> +    return -1
> +}
> +
> +if ![runto_main] {
> +    untested "could not run to main"
> +    return -1
> +}
> +
> +set supports_pkru 0
> +set test "probe PKRU support"
> +gdb_test_multiple "print have_pkru()" $test {
> +    -re ".. = 1\r\n$gdb_prompt $" {
> +        pass $test
> +        set supports_pkru 1
> +    }
> +    -re ".. = 0\r\n$gdb_prompt $" {
> +        pass $test
> +    }
> +}
> +
> +if { !$supports_pkru } {
> +    unsupported "processor does not support protection key feature."
> +    return
> +}
> +
> +# Test pkru register at startup
> +set test_string "0"
> +
> +gdb_test "print \$pkru" $test_string "pkru formating"
> +
> +# Read values from pseudo registers.
> +gdb_breakpoint [ gdb_get_line_number "break here 1" ]
> +gdb_continue_to_breakpoint "break here 1" ".*break here 1.*"
> +
> +set test_string ".*0x12345678.*"
> +gdb_test "info register pkru" ".*pkru$test_string" "read pkru register"
> +
> +set test_string ".*0x44444444.*"
> +gdb_test "print /x \$pkru = 0x44444444" "= 0x44444444" "set pkru value"
> +gdb_test "info register pkru" ".*pkru$test_string" "read value after setting value"

There doesn't seem to be much point to the "test_string" indirection; 
it's used only once each time.

Thanks,
Pedro Alves