Intel IA-32 Manuale Utente

9-22 Vol. 3A

In this example, the Intel assembler ASM386 and build tools BLD386 are used to assemble and
build the initialization code module. The following assumptions are used when using the Intel
ASM386 and BLD386 tools.

•

The ASM386 will generate the right operand size opcodes according to the code-segment
attribute. The attribute is assigned either by the ASM386 invocation controls or in the
code-segment definition.

•

If a code segment that is going to run in real-address mode is defined, it must be set to a
USE 16 attribute. If a 32-bit operand is used in an instruction in this code segment (for
example, MOV EAX, EBX), the assembler automatically generates an operand prefix for
the instruction that forces the processor to execute a 32-bit operation, even though its
default code-segment attribute is 16-bit.

•

Intel's ASM386 assembler allows specific use of the 16- or 32-bit instructions, for
example, LGDTW, LGDTD, IRETD. If the generic instruction LGDT is used, the default-
segment attribute will be used to generate the right opcode.

196

218

Copy the application's GDT from ROM into RAM

220

238

Copy the application's IDT from ROM into RAM

241

243

Load application's GDTR

244

245

Load application's IDTR

247

261

Copy the application's TSS from ROM into RAM

263

267

Update TSS descriptor and other aliases in GDT (GDT alias or IDT alias) 

277

277

Load the task register (without task switch) using LTR instruction

282

286

Load SS, ESP with the value found in the application's TSS

287

287

Push EFLAGS value found in the application's TSS

288

288

Push CS value found in the application's TSS

289

289

Push EIP value found in the application's TSS

290

293

Load DS, ES with the value found in the application's TSS

296

296

Perform IRET; pop the above values and enter the application code