The IA32 version of "SmmInit.nasm" does not need "gSmmJmpAddr" at all (its
PiSmmCpuSmmInitFixupAddress() variant doesn't do anything either). We can
simply use the NASM syntax for the following Mixed-Size Jump:
> jmp PROTECT_MODE_CS : dword @32bit
The generated object code for the instruction is unchanged:
> 00000182 66EA5A0000000800 jmp dword 0x8:0x5a
(The NASM manual explains that putting the DWORD prefix after the colon
":" reflects the intent better, since it is the offset that is a DWORD.
Thus, that's what I used. However, both syntaxes are interchangeable,
hence the ndisasm output.)
The X64 version of "SmmInit.nasm" appears to require "gSmmJmpAddr";
however that's accidental, not inherent:
- Bring LONG_MODE_CODE_SEGMENT from
"UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h" to "SmmInit.nasm" as
LONG_MODE_CS, same as PROTECT_MODE_CODE_SEGMENT was brought to the IA32
version as PROTECT_MODE_CS earlier.
- Apply the NASM-native Mixed-Size Jump syntax again, but jump to the
fixed zero offset in LONG_MODE_CS. This will produce no relocation
record at all. Add a label after the instruction.
- Modify PiSmmCpuSmmInitFixupAddress() to patch the jump target backwards
from the label. Because we modify the DWORD offset with a DWORD access,
the segment selector is unharmed in the instruction, and we need not set
it from PiCpuSmmEntry().
According to "objdump --reloc", the X64 version undergoes only the
following relocations, after this patch:
> RELOCATION RECORDS FOR [.text]:
> OFFSET TYPE VALUE
> 0000000000000095 R_X86_64_PC32 SmmInitHandler-0x0000000000000004
> 00000000000000e0 R_X86_64_PC32 mRebasedFlag-0x0000000000000004
> 00000000000000ea R_X86_64_PC32 mSmmRelocationOriginalAddress-0x0000000000000004
Therefore the patch does not regress
<https://bugzilla.tianocore.org/show_bug.cgi?id=849> ("Enable XCODE5 tool
chain for UefiCpuPkg with nasm source code").
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>
456c4ccab2