This version of save/restore general register seems a bit too ugly, I
will change it and commit another patch.
Some of the registers cannot be set as realmode.c do, for example %rax
used to save return value, wrong %esp %ebp may cause crash, and I
think changed %rflags may cause some unknown error. So these registers
should not be set by caller.
Arthur
On Thu, Jun 6, 2013 at 11:24 PM, Arthur Chunqi Li <yzt356@xxxxxxxxx> wrote:
> Add a function trap_emulator to run an instruction in emulator.
> Set inregs first (%rax is invalid because it is used as return
> address), put instruction codec in alt_insn and call func with
> alt_insn_length. Get results in outregs.
>
> Signed-off-by: Arthur Chunqi Li <yzt356@xxxxxxxxx>
> ---
> x86/emulator.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 81 insertions(+)
>
> diff --git a/x86/emulator.c b/x86/emulator.c
> index 96576e5..8ab9904 100644
> --- a/x86/emulator.c
> +++ b/x86/emulator.c
> @@ -11,6 +11,14 @@ int fails, tests;
>
> static int exceptions;
>
> +struct regs {
> + u64 rax, rbx, rcx, rdx;
> + u64 rsi, rdi, rsp, rbp;
> + u64 rip, rflags;
> +};
> +
> +static struct regs inregs, outregs;
> +
> void report(const char *name, int result)
> {
> ++tests;
> @@ -685,6 +693,79 @@ static void test_shld_shrd(u32 *mem)
> report("shrd (cl)", *mem == ((0x12345678 >> 3) | (5u << 29)));
> }
>
> +static void trap_emulator(uint64_t *mem, uint8_t *insn_page,
> + uint8_t *alt_insn_page, void *insn_ram,
> + uint8_t *alt_insn, int alt_insn_length)
> +{
> + ulong *cr3 = (ulong *)read_cr3();
> + int i;
> +
> + // Pad with RET instructions
> + memset(insn_page, 0xc3, 4096);
> + memset(alt_insn_page, 0xc3, 4096);
> +
> + // Place a trapping instruction in the page to trigger a VMEXIT
> + insn_page[0] = 0x89; // mov %eax, (%rax)
> + insn_page[1] = 0x00;
> + insn_page[2] = 0x90; // nop
> + insn_page[3] = 0xc3; // ret
> +
> + // Place the instruction we want the hypervisor to see in the alternate page
> + for (i=0; i<alt_insn_length; i++)
> + alt_insn_page[i] = alt_insn[i];
> +
> + // Save general registers
> + asm volatile(
> + "push %rax\n\r"
> + "push %rbx\n\r"
> + "push %rcx\n\r"
> + "push %rdx\n\r"
> + "push %rsi\n\r"
> + "push %rdi\n\r"
> + );
> + // Load the code TLB with insn_page, but point the page tables at
> + // alt_insn_page (and keep the data TLB clear, for AMD decode assist).
> + // This will make the CPU trap on the insn_page instruction but the
> + // hypervisor will see alt_insn_page.
> + install_page(cr3, virt_to_phys(insn_page), insn_ram);
> + invlpg(insn_ram);
> + // Load code TLB
> + asm volatile("call *%0" : : "r"(insn_ram + 3));
> + install_page(cr3, virt_to_phys(alt_insn_page), insn_ram);
> + // Trap, let hypervisor emulate at alt_insn_page
> + asm volatile(
> + "call *%1\n\r"
> +
> + "mov %%rax, 0+%[outregs] \n\t"
> + "mov %%rbx, 8+%[outregs] \n\t"
> + "mov %%rcx, 16+%[outregs] \n\t"
> + "mov %%rdx, 24+%[outregs] \n\t"
> + "mov %%rsi, 32+%[outregs] \n\t"
> + "mov %%rdi, 40+%[outregs] \n\t"
> + "mov %%rsp,48+ %[outregs] \n\t"
> + "mov %%rbp, 56+%[outregs] \n\t"
> +
> + /* Save RFLAGS in outregs*/
> + "pushf \n\t"
> + "popq 72+%[outregs] \n\t"
> + : [outregs]"+m"(outregs)
> + : "r"(insn_ram),
> + "a"(mem), "b"(inregs.rbx),
> + "c"(inregs.rcx), "d"(inregs.rdx),
> + "S"(inregs.rsi), "D"(inregs.rdi)
> + : "memory", "cc"
> + );
> + // Restore general registers
> + asm volatile(
> + "pop %rax\n\r"
> + "pop %rbx\n\r"
> + "pop %rcx\n\r"
> + "pop %rdx\n\r"
> + "pop %rsi\n\r"
> + "pop %rdi\n\r"
> + );
> +}
> +
> static void advance_rip_by_3_and_note_exception(struct ex_regs *regs)
> {
> ++exceptions;
> --
> 1.7.9.5
>
--
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China
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