> 2. This patch also hits NOP sleds > 8 bytes on i386. We could also hit
> the NOP sleds between 3 and 7 bytes if there are no objections.
The attached diff implements the same trapsled mechanism for i386 and
amd64 for all padding sequences between 3 and 15 bytes.
I have put this through a kernel and base build on i386 without apparent
ill effect, and the amd64 parts are unchanged from the last diff.
Todd
Index: gas/config/tc-i386.c
===================================================================
RCS file: /cvs/src/gnu/usr.bin/binutils-2.17/gas/config/tc-i386.c,v
retrieving revision 1.7
diff -u -p -u -p -r1.7 tc-i386.c
--- gas/config/tc-i386.c 4 Jun 2017 20:26:18 -0000 1.7
+++ gas/config/tc-i386.c 21 Jun 2017 00:43:14 -0000
@@ -505,41 +505,9 @@ i386_align_code (fragP, count)
{0x90}; /* nop */
static const char f32_2[] =
{0x89,0xf6}; /* movl %esi,%esi */
- static const char f32_3[] =
- {0x8d,0x76,0x00}; /* leal 0(%esi),%esi */
- static const char f32_4[] =
- {0x8d,0x74,0x26,0x00}; /* leal 0(%esi,1),%esi */
- static const char f32_5[] =
- {0x90, /* nop */
- 0x8d,0x74,0x26,0x00}; /* leal 0(%esi,1),%esi */
- static const char f32_6[] =
- {0x8d,0xb6,0x00,0x00,0x00,0x00}; /* leal 0L(%esi),%esi */
- static const char f32_7[] =
- {0x8d,0xb4,0x26,0x00,0x00,0x00,0x00}; /* leal 0L(%esi,1),%esi */
- static const char f32_8[] =
- {0x90, /* nop */
- 0x8d,0xb4,0x26,0x00,0x00,0x00,0x00}; /* leal 0L(%esi,1),%esi */
- static const char f32_9[] =
- {0x89,0xf6, /* movl %esi,%esi
*/
- 0x8d,0xbc,0x27,0x00,0x00,0x00,0x00}; /* leal 0L(%edi,1),%edi */
- static const char f32_10[] =
- {0x8d,0x76,0x00, /* leal 0(%esi),%esi */
- 0x8d,0xbc,0x27,0x00,0x00,0x00,0x00}; /* leal 0L(%edi,1),%edi */
- static const char f32_11[] =
- {0x8d,0x74,0x26,0x00, /* leal 0(%esi,1),%esi */
- 0x8d,0xbc,0x27,0x00,0x00,0x00,0x00}; /* leal 0L(%edi,1),%edi */
- static const char f32_12[] =
- {0x8d,0xb6,0x00,0x00,0x00,0x00, /* leal 0L(%esi),%esi */
- 0x8d,0xbf,0x00,0x00,0x00,0x00}; /* leal 0L(%edi),%edi */
- static const char f32_13[] =
- {0x8d,0xb6,0x00,0x00,0x00,0x00, /* leal 0L(%esi),%esi */
- 0x8d,0xbc,0x27,0x00,0x00,0x00,0x00}; /* leal 0L(%edi,1),%edi */
- static const char f32_14[] =
- {0x8d,0xb4,0x26,0x00,0x00,0x00,0x00, /* leal 0L(%esi,1),%esi */
- 0x8d,0xbc,0x27,0x00,0x00,0x00,0x00}; /* leal 0L(%edi,1),%edi */
static const char f32_15[] =
- {0xeb,0x0d,0x90,0x90,0x90,0x90,0x90, /* jmp .+15; lotsa nops */
- 0x90,0x90,0x90,0x90,0x90,0x90,0x90,0x90};
+ {0xeb,0x0d,0xCC,0xCC,0xCC,0xCC,0xCC, /* jmp .+15; lotsa int3 */
+ 0xCC,0xCC,0xCC,0xCC,0xCC,0xCC,0xCC,0xCC};
static const char f16_3[] =
{0x8d,0x74,0x00}; /* lea 0(%esi),%esi */
static const char f16_4[] =
@@ -556,40 +524,31 @@ i386_align_code (fragP, count)
static const char f16_8[] =
{0x8d,0xb4,0x00,0x00, /* lea 0w(%si),%si */
0x8d,0xbd,0x00,0x00}; /* lea 0w(%di),%di */
+ static const char f64_2[] =
+ {0x66,0x90}; /* data16, nop*/
static const char *const f32_patt[] = {
- f32_1, f32_2, f32_3, f32_4, f32_5, f32_6, f32_7, f32_8,
- f32_9, f32_10, f32_11, f32_12, f32_13, f32_14, f32_15
+ f32_1, f32_2, f32_15, f32_15, f32_15, f32_15, f32_15, f32_15,
+ f32_15, f32_15, f32_15, f32_15, f32_15, f32_15, f32_15
};
static const char *const f16_patt[] = {
f32_1, f32_2, f16_3, f16_4, f16_5, f16_6, f16_7, f16_8,
f32_15, f32_15, f32_15, f32_15, f32_15, f32_15, f32_15
};
+ static const char *const f64_patt[] = {
+ f32_1, f64_2, f32_15, f32_15, f32_15, f32_15, f32_15, f32_15,
+ f32_15, f32_15, f32_15, f32_15, f32_15, f32_15, f32_15
+ };
if (count <= 0 || count > 15)
return;
- /* The recommended way to pad 64bit code is to use NOPs preceded by
- maximally four 0x66 prefixes. Balance the size of nops. */
if (flag_code == CODE_64BIT)
{
- int i;
- int nnops = (count + 3) / 4;
- int len = count / nnops;
- int remains = count - nnops * len;
- int pos = 0;
-
- for (i = 0; i < remains; i++)
- {
- memset (fragP->fr_literal + fragP->fr_fix + pos, 0x66, len);
- fragP->fr_literal[fragP->fr_fix + pos + len] = 0x90;
- pos += len + 1;
- }
- for (; i < nnops; i++)
- {
- memset (fragP->fr_literal + fragP->fr_fix + pos, 0x66, len - 1);
- fragP->fr_literal[fragP->fr_fix + pos + len - 1] = 0x90;
- pos += len;
- }
+ memcpy(fragP->fr_literal + fragP->fr_fix,
+ f64_patt[count -1], count);
+ if (count > 2)
+ /* Adjust jump offset */
+ fragP->fr_literal[fragP->fr_fix + 1] = count - 2;
}
else
if (flag_code == CODE_16BIT)
@@ -601,8 +560,13 @@ i386_align_code (fragP, count)
fragP->fr_literal[fragP->fr_fix + 1] = count - 2;
}
else
+ {
memcpy (fragP->fr_literal + fragP->fr_fix,
f32_patt[count - 1], count);
+ if (count > 2)
+ /* Adjust jump offset */
+ fragP->fr_literal[fragP->fr_fix + 1] = count - 2;
+ }
fragP->fr_var = count;
}
