[Bug middle-end/26565] New: Unaligned accesses with __attribute__(packed) and memcpy

["falk at debian dot org" <gcc-bugzilla at gcc dot gnu dot org>]

gcc version 4.2.0 20060304 (experimental)

falk@juist:/tmp% cat test.c
void *memcpy(void *dest, const void *src, __SIZE_TYPE__ n);

struct timeval {
    long tv_sec;
};

struct outdata {
    char seq;
    struct timeval tv __attribute__((packed));
};

void send_probe(struct outdata *outdata, struct timeval *tp) {
    memcpy(&outdata->tv, tp, sizeof outdata->tv);
}

falk@juist:/tmp% gcc-3.4 -c -O3 test.c && objdump -dr test.o 
0000000000000000 <send_probe>:
   0:   00 00 51 a6     ldq     a2,0(a1)
   4:   08 00 10 2d     ldq_u   t7,8(a0)
   8:   01 00 70 20     lda     t2,1(a0)
   c:   01 00 f0 2c     ldq_u   t6,1(a0)
  10:   e5 0e 43 4a     insqh   a2,t2,t4
  14:   64 07 43 4a     insql   a2,t2,t3
  18:   46 0e 03 49     mskqh   t7,t2,t5
  1c:   40 06 e3 48     mskql   t6,t2,v0
  20:   01 04 c5 44     or      t5,t4,t0
  24:   08 00 30 3c     stq_u   t0,8(a0)
  28:   02 04 04 44     or      v0,t3,t1
  2c:   01 00 50 3c     stq_u   t1,1(a0)
  30:   01 80 fa 6b     ret

falk@juist:/tmp% gcc -c -O3 test.c && objdump -dr test.o     
0000000000000000 <send_probe>:
   0:   00 00 31 a4     ldq     t0,0(a1)
   4:   01 00 30 b4     stq     t0,1(a0)
   8:   01 80 fa 6b     ret

So 3.4 accounts for an unaligned access, but mainline doesn't.
This has been broken since 4.0. Just reading outdata->tv.tv_sec works fine.


-- 
           Summary: Unaligned accesses with __attribute__(packed) and memcpy
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Keywords: wrong-code
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: falk at debian dot org
 GCC build triplet: alphaev68-linux-gnu
  GCC host triplet: alphaev68-linux-gnu
GCC target triplet: alphaev68-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26565