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copied!<p><strong><em>New answer:</em></strong></p> <p>I've already encounter this problem some time ago and the only way I found to update the GDT with MASM inline assembly is to use a far return instruction, instead of the far jump instruction. </p> <pre><code>struct gdt_entry gdt[3]; struct gdt_ptr gp; void gdt_flush(){ __asm{ lgdt [gp] mov ax, 0x10 mov ds, ax mov es, ax mov fs, ax mov gs, ax mov ss, ax ; push the address on the stack push 0x08 mov eax, offset flush2 push eax ; ret use the previous pushed address _emit 0xCB ; far return flush2: ;ret } } </code></pre> <p>As far as I remember, there are two problems:</p> <ul> <li>the 32 bits MASM inline assembly cannot compile far instructions, so you have to emit the opcode.</li> <li>the <code>jmp</code> instruction does not do the right stuff and you should use instead the <code>ret</code> instruction to jump to the next line of code.</li> </ul> <p>Also, don't call the ret instruction from the inline assembly, otherwise you'll skip the epilog code that the compiler puts at the end of the function to clean the stack.</p> <hr> <p><strong><em>My first answer below:</em></strong></p> <p>Maybe your GDT descriptor (gp) is badly initialized. </p> <p>When you the jump instruction is executed, the processor try to switch to protected mode and the GDT is then required. If the GDT is not set correctly, it crashed.</p> <p>The first 16 bits of gp are the size of the gdt (here 3*8 = 24 bytes) and the following 32 bytes are the address of the gdt (here &gdt[0]).</p> <p>Also, make sure the ds register is null before calling lgdt: this register is used by the instruction.</p>

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