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Re: [Xen-devel] [PATCH 02/17] x86emul: fetch all insn bytes during the decode phase

On 14/09/16 10:55, Jan Beulich wrote:
On 13.09.16 at 20:44, <andrew.cooper3@xxxxxxxxxx> wrote:
On 08/09/16 14:07, Jan Beulich wrote:
@@ -1602,6 +1602,45 @@ struct x86_emulate_state {
  #define _regs (state->regs)
static int
What do you mean by decode_base here?
The base instruction set (no 0f or alike prefixes). Suggestions for
a better name welcome.

x86_decode_onebyte() to match the table of opcodes it is further decoding.

@@ -2644,18 +2704,13 @@ x86_emulate(
case 0x9a: /* call (far, absolute) */ {
          struct segment_register reg;
-        uint16_t sel;
-        uint32_t eip;
- generate_exception_if(mode_64bit(), EXC_UD, -1);
+        ASSERT(!mode_64bit());
Are we going to strictly require that noone ever hand-crafts a
x86_emulate_state and hands it to x86_emulate()?
Absolutely - that's why its definition does not live in a header.


I would suggest leaving the generate_exception_if(mode_64bit(), EXC_UD,
-1); after the ASSERT() so even if we do end up in a wonky state, we
don't try to jump the guest to 0.
That would look really strange to a reader, I think, and hence I'd
rather not do this if I can get the patch accepted without.

It is conceptually no different to



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