RE: [PATCH] x86: allow 32-bit reg to be used with U{RD,WR}MSR

["Hu, Lin1" <lin1.hu@intel.com>]

I talked to the people involved. They found the eds description about "ignoring h32 bits of the MSR address for register variants" is a documentation bug. The right version is USER_MSR have a GP fault on h32 of the MSR address for the register version. So they update the description from #GP(0) If MSR_address[63:0] & 0x0000_0000_FFFF_C000 != 0
to #GP(0) If MSR_address[63:0] & 0xFFFF_FFFF_FFFF_C000 != 0. And the source register will still be r64 in the spec.

BRs,
Lin

> -----Original Message-----
> From: Jan Beulich <jbeulich@suse.com>
> Sent: Friday, November 24, 2023 5:18 PM
> To: Binutils <binutils@sourceware.org>
> Cc: H.J. Lu <hjl.tools@gmail.com>; Hu, Lin1 <lin1.hu@intel.com>
> Subject: [PATCH] x86: allow 32-bit reg to be used with U{RD,WR}MSR
> 
> ... as MSR index specifier: It is unreasonable to demand that people write
> less readable / understandable code, just because the present
> documentation mentions only Reg64. Whether to also adjust the
> disassembler is a separate question, perhaps indeed more tightly tied to
> what the spec says.
> 
> --- a/gas/testsuite/gas/i386/x86-64-user_msr.s
> +++ b/gas/testsuite/gas/i386/x86-64-user_msr.s
> @@ -5,7 +5,7 @@ _start:
>  	urdmsr	%r14, %r12
>  	urdmsr	%r14, %rax
>  	urdmsr	%rdx, %r12
> -	urdmsr	%rdx, %rax
> +	urdmsr	%edx, %rax
>  	urdmsr	$51515151, %r12
>  	urdmsr	$51515151, %rax
>  	urdmsr	$0x7f, %r12
> @@ -14,7 +14,7 @@ _start:
>  	uwrmsr	%r12, %r14
>  	uwrmsr	%rax, %r14
>  	uwrmsr	%r12, %rdx
> -	uwrmsr	%rax, %rdx
> +	uwrmsr	%rax, %edx
>  	uwrmsr	%r12, $51515151
>  	uwrmsr	%rax, $51515151
>  	uwrmsr	%r12, $0x7f
> @@ -24,7 +24,7 @@ _start:
>  	.intel_syntax noprefix
>  	urdmsr	r12, r14
>  	urdmsr	rax, r14
> -	urdmsr	r12, rdx
> +	urdmsr	r12, edx
>  	urdmsr	rax, rdx
>  	urdmsr	r12, 51515151
>  	urdmsr	rax, 51515151
> @@ -33,7 +33,7 @@ _start:
>  	urdmsr	r12, 0x80000000
>  	uwrmsr	r14, r12
>  	uwrmsr	r14, rax
> -	uwrmsr	rdx, r12
> +	uwrmsr	edx, r12
>  	uwrmsr	rdx, rax
>  	uwrmsr	51515151, r12
>  	uwrmsr	51515151, rax
> --- a/opcodes/i386-opc.tbl
> +++ b/opcodes/i386-opc.tbl
> @@ -3359,9 +3359,9 @@ eretu, 0xf30f01ca, FRED, NoSuf, {}
> 
>  // USER_MSR instructions.
> 
> -urdmsr, 0xf20f38f8, USER_MSR, RegMem|NoSuf|NoRex64, { Reg64, Reg64 }
> +urdmsr, 0xf20f38f8, USER_MSR, RegMem|NoSuf|NoRex64, { Reg32|Reg64,
> +Reg64 }
>  urdmsr, 0xf2f8/0, USER_MSR, Modrm|Vex128|VexMap7|VexW0|NoSuf,
> { Imm32, Reg64 } -uwrmsr, 0xf30f38f8, USER_MSR, Modrm|NoSuf|NoRex64,
> { Reg64, Reg64 }
> +uwrmsr, 0xf30f38f8, USER_MSR, Modrm|NoSuf|NoRex64, { Reg64,
> Reg32|Reg64
> +}
>  // Immediates want to be first; md_assemble() takes care of swapping
> operands  // accordingly.
>  uwrmsr, 0xf3f8/0, USER_MSR, Modrm|Vex128|VexMap7|VexW0|NoSuf,
> { Imm32, Reg64 }