On Thu, Jun 13, 2013 at 4:50 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> Il 06/06/2013 11:24, Arthur Chunqi Li ha scritto:
>> 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"
>> + );
>
> This will not work if GCC is using rsp-relative addresses to access
> local variables. You need to use mov instructions to load from inregs,
> and put the push/pop sequences inside the "main" asm that does the "call
> *%1".
Is there any way to let gcc use absolute address to access variables?
I move variant "save" to the global and use "xchg %%rax, 0+%[save]"
and it seems that addressing for "save" is wrong.
Arthur
>
> Paolo
>
>> + // 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;
>>
>
--
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China
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