[Xen-devel] Re: [RFC, PATCH 5/24] i386 Vmi code patching

[Chuck Ebbert <76306.1226@xxxxxxxxxxxxxx>]

In-Reply-To: <200603222115.46926.ak@xxxxxxx>

On Wed, 22 Mar 2006 21:15:44 +0100, Andi Kleen wrote:

> On Monday 13 March 2006 19:02, Zachary Amsden wrote:
> > The VMI ROM detection and code patching mechanism is illustrated in
> > setup.c.  There ROM is a binary block published by the hypervisor, and
> > and there are certainly implications of this.  ROMs certainly have a
> > history of being proprietary, very differently licensed pieces of
> > software, and mostly under non-free licenses.  Before jumping to the
> > conclusion that this is a bad thing, let us consider more carefully
> > why hiding the interface layer to the hypervisor is actually a good
> > thing.
> 
> How about you fix all these issues you describe here first 
> and then submit it again?
> 
> The disassembly stuff indeed doesn't look like something
> that belongs in the kernel.

I think they put the disassembler in there as a joke. ;)

It's not necessary for fixing up the call site, anyway. Something like
this should work, assuming there is always a call in every vmi
translation.


 /* Now, measure and emit the vmi translation sequence */
 #define vmi_translation_start                  \
        .pushsection .vmi.translation,"ax";     \
        781:;
 #define vmi_translation_finish                 \
-       782:;                                   \
+       783:;                                   \
        .popsection;
 #define vmi_translation_begin  781b
-#define vmi_translation_end    782b
+#define vmi_call_location      782b
+#define vmi_translation_end    783b
 #define vmi_translation_len    (vmi_translation_end - vmi_translation_begin)
+#define vmi_call_offset        (vmi_call_location - vmi_translation_begin)

 #define vmi_call(name)                                         \
-       call .+5+name
+       782: call .+5+name

 #define vmi_annotate(name)                             \
        .pushsection .vmi.annotation,"a";               \
        .align 4;                                       \
        .long name;                                     \
        .long vmi_padded_begin;                         \
        .long vmi_translation_begin;                    \
        .byte vmi_padded_len;                           \
        .byte vmi_translation_len;                      \
        .byte vmi_pad_total;                            \
-       .byte 0;                                        \
+       .byte vmi_call_offset;                          \
        .popsection;

 struct vmi_annotation {
        unsigned long   vmi_call;
        unsigned char   *nativeEIP;
        unsigned char   *translationEIP;
        unsigned char   native_size;
        unsigned char   translation_size;
        char            nop_size;
-       unsigned char   pad;
+       unsigned char   call_offset;
 };

 static void fixup_translation(struct vmi_annotation *a)
 {
        unsigned char *c, *start, *end;
        int left;
 
        memcpy(a->nativeEIP, a->translationEIP, a->translation_size);
+       patch_call_site(a, a->nativeEIP + a->call_offset);
-       start = a->nativeEIP;
-       end = a->nativeEIP + a->translation_size;
-
-       for (c = start; c < end;) {
-               switch(*c) {
-                       case MNEM_CALL_NEAR:
-                               patch_call_site(a, c);
-                               c+=5;
-                               break;
-
-                       case MNEM_PUSH_I:
-                               c+=5;
-                               break;
-
-                       case MNEM_PUSH_IB:
-                               c+=2;
-                               break;
-
-                       case MNEM_PUSH_EAX:
-                       case MNEM_PUSH_ECX:
-                       case MNEM_PUSH_EDX:
-                       case MNEM_PUSH_EBX:
-                       case MNEM_PUSH_EBP:
-                       case MNEM_PUSH_ESI:
-                       case MNEM_PUSH_EDI: 
-                               c+=1;
-                               break;
-
-                       case MNEM_LEA:
-                               BUG_ON(*(c+1) != 0x64);  /* [--][--]+disp8, 
%esp */
-                               BUG_ON(*(c+2) != 0x24);  /* none + %esp */
-                               c+=4;
-                               break;
-
-                       default:
-                               /*
-                                * Don't printk - it may acquire spinlocks with
-                                * partially completed VMI translations, causing
-                                * nuclear meltdown of the core.
-                                */
-                               BUG();
-                               return;
-               }
-       }

-- 
Chuck
"Penguins don't come from next door, they come from the Antarctic!"

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