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). Second, when I remove the semicolon, NASM indeed complains in 32-bit mode "error: instruction not supported in 32-bit mode". But the following does work: BITS 64 rep vmmcall BITS 32 and for it, NASM generates the bytes seen above (f3 0f 01 d9). 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 Thanks! Laszlo -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#48292): https://edk2.groups.io/g/devel/message/48292 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] -=-=-=-=-=-=-=-=-=-=-=-
