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Re: [Xen-devel] [PATCH] x86_emulate: properly do IP updates and other side effects on success



Il 07/08/2014 15:24, Fabio Fantoni ha scritto:
Il 07/08/2014 10:30, Jan Beulich ha scritto:
The two MMX/SSE/AVX code blocks failed to update IP properly, and these
as well as get_reg_refix(), which "manually" updated IP so far, failed
to do the TF and RF processing needed at the end of successfully
emulated instructions.

Reported-by: Andrei LUTAS <vlutas@xxxxxxxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Tested-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>

Thanks for the patch, I tested it to see if solves also qxl on linux domUs problem but with this patch the domU crashes and I cannot get a backtrace or specific errors. xl create is ok, gdb on qemu close on domU's crash without having backtrace and in xl dmesg I not saw errors. Setting preserve always in xl cfg I can only see that crash and do a core dump but I not know how to use it to take a backtrace or any other useful information. Someone can explain how to debug the problem for post all useful informations please?
In attachment for now I put xl -vvv create and xl dmesg output.

Thanks for any reply and sorry for my bad english.

Now I also tried gdbsx:
gdbsx -a 2 64 9999
...
(gdb) target remote localhost:9999
Remote debugging using localhost:9999
[Switching to Remote target]
0x66666666 in ?? ()
(gdb) c
Continuing.

Program received signal SIGINT, Interrupt.
0x000000ff in ?? ()
(gdb) bt full
#0  0x000000ff in ?? ()
No symbol table info available.
Cannot access memory at address 0x6d2966c0

I not know if what I did is correct.



--- a/xen/arch/x86/x86_emulate/x86_emulate.c
+++ b/xen/arch/x86/x86_emulate/x86_emulate.c
@@ -720,29 +720,26 @@ do{ uint8_t stub[] = { _bytes, 0xc3 };
put_fpu(&fic); \
  } while (0)
  -static unsigned long __get_rep_prefix(
-    struct cpu_user_regs *int_regs,
-    struct cpu_user_regs *ext_regs,
+static unsigned long _get_rep_prefix(
+    const struct cpu_user_regs *int_regs,
      int ad_bytes)
  {
-    unsigned long ecx = ((ad_bytes == 2) ? (uint16_t)int_regs->ecx :
-                         (ad_bytes == 4) ? (uint32_t)int_regs->ecx :
-                         int_regs->ecx);
-
-    /* Skip the instruction if no repetitions are required. */
-    if ( ecx == 0 )
-        ext_regs->eip = int_regs->eip;
-
-    return ecx;
+    return (ad_bytes == 2) ? (uint16_t)int_regs->ecx :
+           (ad_bytes == 4) ? (uint32_t)int_regs->ecx :
+           int_regs->ecx;
  }
#define get_rep_prefix() ({ \ unsigned long max_reps = 1; \ if ( rep_prefix() ) \ - max_reps = __get_rep_prefix(&_regs, ctxt->regs, ad_bytes); \ + max_reps = _get_rep_prefix(&_regs, ad_bytes); \ if ( max_reps == 0 ) \ - goto done; \
- max_reps; \
+ { \
+ /* Skip the instruction if no repetitions are required. */ \ + dst.type = OP_NONE; \ + goto writeback; \
+ } \
+ max_reps; \
  })
    static void __put_rep_prefix(
@@ -3921,7 +3918,8 @@ x86_emulate(
          if ( !rc && (b & 1) && (ea.type == OP_MEM) )
              rc = ops->write(ea.mem.seg, ea.mem.off, mmvalp,
                              ea.bytes, ctxt);
-        goto done;
+        dst.type = OP_NONE;
+        break;
      }
        case 0x20: /* mov cr,reg */
@@ -4188,7 +4186,8 @@ x86_emulate(
          if ( !rc && (b != 0x6f) && (ea.type == OP_MEM) )
              rc = ops->write(ea.mem.seg, ea.mem.off, mmvalp,
                              ea.bytes, ctxt);
-        goto done;
+        dst.type = OP_NONE;
+        break;
      }
        case 0x80 ... 0x8f: /* jcc (near) */ {







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