On Thu, Jun 13, 2013 at 05:30:03PM +0800, 李春奇 <Arthur Chunqi Li> wrote: > Hi Gleb, > I'm trying to solve these problems in the past days and meet many > difficulties. You want to save all the general registers in calling > insn_page, so registers should be saved to (save) in insn_page. > Because all the instructions should be generated outside and copy to > insn_page, and the instructions generated outside is RIP-relative, so > inside insn_page (save) will be wrong pointed with RIP-relative code. > They do not have to be generated outside. You can write code into insn_page directly. Something like this outside of any functions: asm(".align 4096\n\t" ".global insn_page\n\t" ".global insn_page_end\n\t" ".global test_insn\n\t" ".global test_insn_end\n\t" "insn_page:" "mov %%rax, outregs \n\t" ... "test_insn:\n\t" "in (%ds), %al\n\t" ". = . + 31\n\t" "test_insn_end:\n\t" "mov outregs, %%rax\n\t" ... "ret\n\t" ".align 4096\n\t" "insn_page_end:\n\t"); Now you copy that into alt_insn_page, put instruction you want to test into test_insn offset and remap alt_insn_page into "insn_page" virtual address. > I have tried to move (save) into insn_page. But when calling > insn_page, data in it can only be read and any instructions like "xchg > %%rax, 0+%[save]" may cause error, because at this time read is from > TLB but write will cause inconsistent. > > Another way is disabling RIP-relative code, but I failed when using > "-mcmodel-large -fno-pic", the binary is also using RIP-relative mode. > Is there any way to totally disable RIP-relative code? Besides, using > this feature may specified to some newer C compiler. This may not be a > good solution. > > If we don't set %rsp and %rbp when executing emulator code, we can > just use “push/pop" to save other general registers. > > If you have any better solutions, please let me know. > > Thanks, > Arthur > > On Thu, Jun 13, 2013 at 12:50 PM, 李春奇 <Arthur Chunqi Li> > <yzt356@xxxxxxxxx> wrote: > > 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 > > > > -- > Arthur Chunqi Li > Department of Computer Science > School of EECS > Peking University > Beijing, China -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html