[Bug target/21387] Unaligned writes on MIPSEL systems after typecast

["maarten at contemplated dot nl" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From maarten at contemplated dot nl  2005-05-05 11:49 -------
(In reply to comment #2)

You are completely right, the code above merely demonstrates what happens when
one writes to an illegal address. The correct version,

*((int32_t *) &a.unaligned_int32) = 0x123456;

does work. Sorry, result of 'compressing' the problem.

My 'unaligned write' problem is, however, still there. I stumbled over it when
trying to compile code where copying of 16 bytes (in a char array) was
implemented as two reads and writes of int64_t. The problem occurs when
typecasting char arrays to integer types, see modified example:

1: 

#include <stdint.h>

int main(int argc, char *argv[]) {
        char x[100];

        *((int32_t *) ((char *) (x))) = 0x123456;           // ok
        *((int32_t *) ((char *) (x+4))) = 0x123456;         // ok
        *((int32_t *) ((char *) (x+1))) = 0x123456;         // fails

        return(0);
        }

2: (more related to original)

#include <stdint.h>

#pragma pack(1)
typedef struct  {
        int8_t  byte;                       // removing this byte, code executes
        char unaligned_int32[4];
        } test_unaligned;
#pragma pack()

int main(int argc, char *argv[]) {
        test_unaligned a;

        *((int32_t *) a.unaligned_int32) = 0x123456;    // fails
 
        return(0);
        }



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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21387