(This patch is the 64-bit variant of commit e75ee97224,
"UefiCpuPkg/PiSmmCpuDxeSmm: remove unneeded DBs from IA32 SmmStartup()",
2018-01-31.)
The SmmStartup() function executes in SMM, which is very similar to real
mode. Add "BITS 16" before it and "BITS 64" after it (just before the
@LongMode label).
Remove the manual 0x66 operand-size override prefixes, for selecting
32-bit operands -- the sizes of our operands trigger NASM to insert the
prefixes automatically in almost every spot. The one place where we have
to add it back manually is the LGDT instruction. In the LGDT instruction
we also replace the binary 0x2E prefix with the normal NASM syntax for CS
segment override.
The stores to the Control Registers were always 32-bit wide; the source
code only used RAX as source operand because it generated the expected
object code (with NASM compiling the source as if in BITS 64). With BITS
16 added, we can use the actual register width in the source operands
(EAX).
This patch causes NASM to generate byte-identical object code (determined
by disassembling both the pre-patch and post-patch versions, and comparing
the listings), except:
> @@ -231,7 +231,7 @@
> 000001D2 6689D3 mov ebx,edx
> 000001D5 66B800000000 mov eax,0x0
> 000001DB 0F22D8 mov cr3,eax
> -000001DE 662E670F0155F6 o32 lgdt [cs:ebp-0xa]
> +000001DE 2E66670F0155F6 o32 lgdt [cs:ebp-0xa]
> 000001E5 66B800000000 mov eax,0x0
> 000001EB 80CC02 or ah,0x2
> 000001EE 0F22E0 mov cr4,eax
The only difference is the prefix list order, it changes from:
- 0x66, 0x2E, 0x67
to
- 0x2E, 0x66, 0x67
Cc: Eric Dong <eric.dong@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=866
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
The majority of the content in the EDK II open source project uses a
BSD 2-Clause License. The EDK II open source project contains
the following components that are covered by additional licenses:
00c5eede48