Re: [PATCH] x86-64: fix ZMM register state tracking

Jan Beulich
2018-09-18T13:38:00Z

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>>> On 10.09.18 at 15:01, <simon.marchi@polymtl.ca> wrote:
> On 2018-09-10 07:25, Jan Beulich wrote:
>>>>> Simon Marchi <simon.marchi@ericsson.com> 09/08/18 1:13 AM >>>
>>> Would it be possible to update or create a test to exercise that?
>>> arch-specific tests are in testsuite/gdb.arch.
>>
>> I'm sure it would be possible, but while I was happy to invest the time
>> to
>> fix the actual bug (because it affects work I'm doing), I'm afraid I
>> don't have
>> the time to learn how gdb test cases are to be constructed (I'm
>> familiar
>> only with the binutils / gas side of things).
>
> I understand. If you can provide:
>
> - a minimal source file (C + assembly in this case, I suppose)
> - GDB commands to reproduce the bug
> - actual and expected output

Attached. vzero.s is the source file used (no C file needed). gdb.log
is a transcript of a session with a broken gdb (the one installed on
the system), while gdb.txt is a transcript for the fixed one that I've
built myself.

> I can take care of turning it in a GDB test case.

Thanks.

Jan

[-- Attachment #2: vzero.s --]
[-- Type: application/octet-stream, Size: 139 bytes --]

.text
.global main
main:
vpternlogd $0xff, %zmm0, %zmm0, %zmm0
vpternlogd $0xff, %zmm0, %zmm0, %zmm16
vzeroupper
xor %eax, %eax
ret

[-- Attachment #3: gdb.log --]
[-- Type: application/octet-stream, Size: 1636 bytes --]

[jbeulich@dus-dev-sles15v ~]$ gcc -Wall -W -o vzero{,.s} && gdb ./vzero
GNU gdb (GDB; SUSE Linux Enterprise 15) 8.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-suse-linux".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://bugs.opensuse.org/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./vzero...done.
(gdb) break main
Breakpoint 1 at 0x400497
(gdb) r
Starting program: /home/jbeulich/vzero

Breakpoint 1, 0x0000000000400497 in main ()
(gdb) disp/i $pc
2: x/i $pc
=> 0x400497 : vpternlogd zmm0,zmm0,zmm0,0xff
(gdb) si
0x000000000040049e in main ()
2: x/i $pc
=> 0x40049e <main+7>: vpternlogd zmm16,zmm0,zmm0,0xff
(gdb)
0x00000000004004a5 in main ()
2: x/i $pc
=> 0x4004a5 <main+14>: vzeroupper
(gdb) print $zmm0.v16_int32
$1 = {-1 <repeats 16 times>}
(gdb) print $zmm16.v16_int32
$2 = {-1 <repeats 16 times>}
(gdb) si
0x00000000004004a8 in main ()
2: x/i $pc
=> 0x4004a8 <main+17>: xor eax,eax
(gdb) print $zmm16.v16_int32
$3 = {-1, -1, -1, -1, -1, -1, -1, -1, 0, 0, 0, 0, 0, 0, 0, 0}
(gdb) q
A debugging session is active.

Inferior 1 [process 56844] will be killed.

Quit anyway? (y or n) y

[-- Attachment #4: gdb.txt --]
[-- Type: text/plain, Size: 1645 bytes --]

[jbeulich@dus-dev-sles15v ~]$ gcc -Wall -W -o vzero{,.s} && gdbx ./vzero
GNU gdb (GDB) 8.1.1
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
<http://www.gnu.org/software/gdb/documentation/>.
For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./vzero...done.
(gdb) break main
Breakpoint 1 at 0x400497
(gdb) r
Starting program: /home/jbeulich/vzero

Breakpoint 1, 0x0000000000400497 in main ()
(gdb) disp/i $pc
2: x/i $pc
=> 0x400497 : vpternlogd zmm0,zmm0,zmm0,0xff
(gdb) si
0x000000000040049e in main ()
2: x/i $pc
=> 0x40049e <main+7>: vpternlogd zmm16,zmm0,zmm0,0xff
(gdb)
0x00000000004004a5 in main ()
2: x/i $pc
=> 0x4004a5 <main+14>: vzeroupper
(gdb) print $zmm0.v16_int32
$1 = {-1 <repeats 16 times>}
(gdb) print $zmm16.v16_int32
$2 = {-1 <repeats 16 times>}
(gdb) si
0x00000000004004a8 in main ()
2: x/i $pc
=> 0x4004a8 <main+17>: xor eax,eax
(gdb) print $zmm16.v16_int32
$3 = {-1 <repeats 16 times>}
(gdb) q
A debugging session is active.

Inferior 1 [process 56857] will be killed.

Quit anyway? (y or n) y