none/tests/ppc64/std_reg_imm.c

   1
   2 /*
   3 This is a regression test for the following problem, noticed by
   4 Greg Parker:
   5
   6 vex ppc64 generates bad code for instruction sequences like this:
   7
   8     li    r0, 2
   9     stdx  r3, r1, r0
  10
  11 gcc emits code like this when manipulating packed structures
  12 with 8-byte fields on 2-byte boundaries.
  13
  14 First, vex's optimizer substitutes a constant 0x2 for r0:
  15
  16     ------ IMark(0x100000F34, 4) ------
  17     PUT(1024) = 0x100000F34:I64
  18     t3 = GET:I64(24)
  19     t14 = GET:I64(8)
  20     t13 = Add64(t14,0x2:I64)
  21     STbe(t13) = t3
  22
  23 Then instruction selection chooses `std` with an index not divisible by 4:
  24
  25     -- STbe(Add64(GET:I64(8),0x2:I64)) = GET:I64(24)
  26     ldz %vR22,8(%r31)
  27     ldz %vR23,24(%r31)
  28     std %vR23,2(%vR22)
  29
  30 Finally, the assembler silently strips the index&3 part,
  31 because `std` can't encode that:
  32
  33     std %r6,2(%r5)
  34     F8 C5 00 00
  35
  36 ...but 0xF8C50000 is `std r6, 0(r5)`, which writes to the wrong address.
  37 */
  38
  39 #include <stdio.h>
  40 #include <stdlib.h>
  41 #include <assert.h>
  42
  43 typedef
  44 struct __attribute__ ((__packed__)) {
  45   char before[2];
  46   unsigned long long int w64;
  47   char after[6];
  48 }
  49 T;
  50
  51 void foo (T* t, unsigned long long int w)
  52 {
  53   __asm__ __volatile__(
  54      "stdx %0,%1,%2"
  55      : : "b"(w), "b"(t), "b"(2) : "memory"
  56   );
  57 }
  58
  59 int main ( void )
  60 {
  61   T* t;
  62   unsigned char* p;
  63   int i;
  64   assert(sizeof(T) == 16);
  65   t = calloc(sizeof(T),1);
  66   assert(t);
  67   /* check t is 8-aligned.  This causes the write done by 'foo' to be
  68      misaligned by 2 as desired, triggering the bug. */
  69   assert(0 == (((unsigned long)t) & 7));
  70   foo(t, 0x1122334455667788);
  71   p = (unsigned char*)t;
  72   for (i = 0; i < 16; i++)
  73     if (p[i] == 0)
  74       printf("..");
  75     else
  76       printf("%02x", (int)p[i]);
  77   printf("\n");
  78   return 0;
  79 }