On 9/30/19 2:29 PM, Laszlo Ersek via Groups.Io wrote: > On 09/24/19 20:57, Lendacky, Thomas wrote: >> On 9/24/19 8:42 AM, Laszlo Ersek wrote: >>> On 09/19/19 21:52, Lendacky, Thomas wrote: > >>>> + ; Issue VMGEXIT (rep; vmmcall) >>>> + db 0xf3 >>>> + db 0x0f >>>> + db 0x01 >>>> + db 0xd9 >>> >>> (8) Can you please file an RFE at <https://bugzilla.nasm.us/>, for >>> supporting this instruction, and add the link here, as a comment? I've >>> been fighting an uphill battle against DB-encoded instructions in edk2 >>> assembly code. >> >> Yes, let me look into that. > > Actually, from peeking ahead at patch "MdePkg/BaseLib: Add support for > the VMGEXIT instruction", it looks like "rep; vmmcall" is already > understood by NASM. > > Can you use that here? > > ... In case that sequence of mnemonics is specific to NASM's 64-bit > mode: can you bracket it with BITS 64 / BITS 32, just so we can avoid > the DBs? Something like (if necessary): > > ; Issue VMGEXIT > BITS 64 > rep; vmmcall > BITS 32 > > > Hmmm why don't I try this out myself... > > ... So, first, the semicolon (;) seems wrong in the NASM source. It > turns vmmcall into a comment, and NASM assembles only the REP prefix (to > a single 0xF3 byte).
Yeah, missed that. I'm so used to the GCC/GAS syntax. > > Second, when I remove the semicolon, NASM indeed complains in 32-bit > mode "error: instruction not supported in 32-bit mode". Right, that was why I moved to the DBs. > > But the following does work: > > BITS 64 > rep vmmcall > BITS 32 > > and for it, NASM generates the bytes seen above (f3 0f 01 d9). Excellent, I'll use that. > > So I suggest: > - using this pattern in the present patch > - using this pattern in the Ia32/VmgExit.nasm source file in the > MdePkg/BaseLib patch > - removing the semicolon in the X64/VmgExit.nasm source file in the > MdePkg/BaseLib patch > Will do. Thanks, Tom > Thanks! > Laszlo > > > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#48298): https://edk2.groups.io/g/devel/message/48298 Mute This Topic: https://groups.io/mt/34203539/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
