------- 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);
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21387
