Re: [PATCH v8 0/1] MR721: ntoskrnl: Implement cmp instruction with opcode 0x83

[Etaash Mathamsetty (＠etaash.mathamsetty)]

On Sat Sep  3 17:53:35 2022 +0000, **** wrote:
> Zebediah Figura replied on the mailing list:
> On 9/3/22 12:48, Etaash Mathamsetty (@etaash.mathamsetty) wrote:
> > On Sat Sep  3 17:43:11 2022 +0000, **** wrote:
> >> Zebediah Figura replied on the mailing list:
> >> \`\`\`
> >> On 9/3/22 12:22, Etaash Mathamsetty (@etaash.mathamsetty) wrote:
> >>> This instruction only needs to compare 1 byte, since it's imm8 is just
> >> an 8 bit number (unless I am wrong)
> >> The 0x83 family is an arithmetic operation between a sign-extended
> >> immediate byte and a 2/4/8-byte register or memory location. The
> >> equivalent 1-byte comparison is 0x80 or 0x82 (they are duplicates).
> >> \`\`\`
> > the comparison is between a signed byte and a 2/4/8 byte
> register/memory location, how am I supposed to compare more than 1 byte?
> > 
> As stated, the immediate byte should be sign-extended to the appropriate 
> length.

Do you have any info on how to set these other flags?  
`OF, PF, AF, SF`  
I can't find much info about it.

[PATCH v8 0/1] MR721: ntoskrnl: Implement cmp instruction with opcode 0x83

[Zebediah Figura]

On 9/3/22 16:10, Etaash Mathamsetty (@etaash.mathamsetty) wrote:
> On Sat Sep  3 17:53:35 2022 +0000, **** wrote:
> > Zebediah Figura replied on the mailing list:
> > On 9/3/22 12:48, Etaash Mathamsetty (@etaash.mathamsetty) wrote:
> > > On Sat Sep  3 17:43:11 2022 +0000, **** wrote:
> > >> Zebediah Figura replied on the mailing list:
> > >> \`\`\`
> > >> On 9/3/22 12:22, Etaash Mathamsetty (@etaash.mathamsetty) wrote:
> > >>> This instruction only needs to compare 1 byte, since it's imm8 is just
> > >> an 8 bit number (unless I am wrong)
> > >> The 0x83 family is an arithmetic operation between a sign-extended
> > >> immediate byte and a 2/4/8-byte register or memory location. The
> > >> equivalent 1-byte comparison is 0x80 or 0x82 (they are duplicates).
> > >> \`\`\`
> > > the comparison is between a signed byte and a 2/4/8 byte
> > register/memory location, how am I supposed to compare more than 1 byte?
> > >
> > As stated, the immediate byte should be sign-extended to the appropriate
> > length.
>
> Do you have any info on how to set these other flags?
> `OF, PF, AF, SF`
> I can't find much info about it.

There are many resources on the x86 architecture online, including the 
official Intel and AMD processor specifications. sandpile.org is another 
unofficial resource which may be easier to browse.