Re: linux-next: Tree for Oct 14 (insn_decoder_test)
From: Randy Dunlap
Date: Wed Nov 27 2019 - 19:04:17 EST
On 10/22/19 10:49 PM, Masami Hiramatsu wrote:
> Hi,
>
> On Mon, 14 Oct 2019 08:30:02 -0700
> Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>
>> On 10/13/19 11:47 PM, Stephen Rothwell wrote:
>>> Hi all,
>>>
>>> Changes since 20191011:
>>>
>>
>> on x86_64:
>>
>> HOSTCC arch/x86/tools/insn_decoder_test
>> HOSTCC arch/x86/tools/insn_sanity
>> TEST posttest
>> arch/x86/tools/insn_decoder_test: warning: Found an x86 instruction decoder bug, please report this.
>> arch/x86/tools/insn_decoder_test: warning: ffffffff81000bf1: f7 0b 00 01 08 00 testl $0x80100,(%rbx)
>> arch/x86/tools/insn_decoder_test: warning: objdump says 6 bytes, but insn_get_length() says 2
>> arch/x86/tools/insn_decoder_test: warning: Decoded and checked 11913894 instructions with 1 failures
>> TEST posttest
>> arch/x86/tools/insn_sanity: Success: decoded and checked 1000000 random instructions with 0 errors (seed:0x871ce29c)
>
> Hmm, curious.
>
> x86-opcode-map.txt said,
> f7: Grp3_2 Ev (1A)
>
> and "0x0b" is 00001011b, Group encoding bits are 5,4,3 (reg field),
> so group index is 001.
>
> GrpTable: Grp3_2
> 0: TEST Ev,Iz
> 1:
>
> Hmm, "f7 0b" is not assigned to any instruction... (testl should be f7 03)
>
> I've checked Intel SDM May 2019 version(*), but the Opcode Map (Table A-6. Opecode
> Extensions for One- and Two-byte Opecodes by Group Number) showed the group index
> 001 is still blank. I've also checked that Table B-13 (General Purpose Instruction
> Formats and Encodings for Non-64-Bit Modes (Note that this has no REX prefix)) but
> I couldn't find "f7 0b".
>
> At last, I found that on AMD64 Architecture Programmer's Manual Volume 3, Appendix A.2
> Table A-6. ModRM.reg Extensions for the Primary Opcode Map(**), which shows that both
> f7 + reg=000 and f7 + reg=001 are same. So only on AMD64, it is officially available
> instruction.
>
> (*) https://software.intel.com/sites/default/files/managed/a4/60/325383-sdm-vol-2abcd.pdf
> (**) https://www.amd.com/system/files/TechDocs/24594.pdf
>
> OK, so this should be fixed with below patch.
>
> ------
>>From b3f45b86df25be59fcf417730ab4c69c6310eaad Mon Sep 17 00:00:00 2001
> From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Date: Wed, 23 Oct 2019 14:45:35 +0900
> Subject: [PATCH] x86/decoder: Add TEST opcode to Group3-2
>
> Add TEST opcode to Group3-2 reg=001b as same as Group3-1 does.
>
> Commit 12a78d43de76 ("x86/decoder: Add new TEST instruction pattern")
> added a TEST opcode assignment to f6 XX/001/XXX (Group 3-1), but not
> added f7 XX/001/XXX (Group 3-2). Actually these TEST opcode is not
> described in Intel SDM Vol2, but described in AMD64 Architecture
> Programmer's Manual Vol.3, Appendix A.2 Table A-6. ModRM.reg
> Extensions for the Primary Opcode Map.
>
> Without this fix, Randy found a warning by insn_decoder_test related
> to this issue as below.
>
> HOSTCC arch/x86/tools/insn_decoder_test
> HOSTCC arch/x86/tools/insn_sanity
> TEST posttest
> arch/x86/tools/insn_decoder_test: warning: Found an x86 instruction decoder bug, please report this.
> arch/x86/tools/insn_decoder_test: warning: ffffffff81000bf1: f7 0b 00 01 08 00 testl $0x80100,(%rbx)
> arch/x86/tools/insn_decoder_test: warning: objdump says 6 bytes, but insn_get_length() says 2
> arch/x86/tools/insn_decoder_test: warning: Decoded and checked 11913894 instructions with 1 failures
> TEST posttest
> arch/x86/tools/insn_sanity: Success: decoded and checked 1000000 random instructions with 0 errors (seed:0x871ce29c)
>
> To fix this error, add TEST opcode according to AMD64 APM Vol.3.
>
> Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Acked-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Tested-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Thanks.
> ---
> arch/x86/lib/x86-opcode-map.txt | 2 +-
> tools/arch/x86/lib/x86-opcode-map.txt | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/lib/x86-opcode-map.txt b/arch/x86/lib/x86-opcode-map.txt
> index e0b85930dd77..4635ce298d1d 100644
> --- a/arch/x86/lib/x86-opcode-map.txt
> +++ b/arch/x86/lib/x86-opcode-map.txt
> @@ -907,7 +907,7 @@ EndTable
>
> GrpTable: Grp3_2
> 0: TEST Ev,Iz
> -1:
> +1: TEST Ev,Iz
> 2: NOT Ev
> 3: NEG Ev
> 4: MUL rAX,Ev
> diff --git a/tools/arch/x86/lib/x86-opcode-map.txt b/tools/arch/x86/lib/x86-opcode-map.txt
> index e0b85930dd77..4635ce298d1d 100644
> --- a/tools/arch/x86/lib/x86-opcode-map.txt
> +++ b/tools/arch/x86/lib/x86-opcode-map.txt
> @@ -907,7 +907,7 @@ EndTable
>
> GrpTable: Grp3_2
> 0: TEST Ev,Iz
> -1:
> +1: TEST Ev,Iz
> 2: NOT Ev
> 3: NEG Ev
> 4: MUL rAX,Ev
>
--
~Randy