Bug#731806: debian-installer: FTBFS on sparc: genisoimage errors
Hi,
On 28/04/2014 18:25, Thomas Schmitt wrote:
has a struct on heap (#L102, #L138, #L146):
struct w_list{
...
union w_list_data
{
...
struct write_opts write;
...
} u;
}
...
struct w_list *a;
...
a = calloc(1, sizeof(struct w_list));
The gesture which causes the SIGBUS is (#L149)
a->u = *(union w_list_data *)data;
The issue is that data needs to be suitably aligned on an appropriate
memory boundary. SPARC requires that int32 accesses are aligned on 4
byte boundaries and that int64 aligns on 8 byte boundaries.
You have to arrange that data is properly aligned or you will get a
SIGBUS due to an address misalignment.
malloc and calloc arrange that the alignment is suitable
(the manpage says)
"RETURN VALUE
The malloc() and calloc() functions return a pointer to the allocated
memory that is suitably aligned for any kind of variable. "
I'm guessing that your void *data isn't directly allocated by calloc so
it doesn't necessarily have the correct alignment.
which is not what i personally would use, but should be fully legal
nevertheless.
The SIGBUS vanishes if i compile without gcc -O2, or if i replace
the "a->u =" gesture by
memcpy(&(a->u), data, sizeof(union w_list_data));
which i deem equivalent (and more my personal style).
The memcpy version will work just fine because memcpy takes
misalignments into account and once the data has been copied into a->u
the calloc'd version of struct w_list will be properly aligned because
calloc guarantees that it will be.
memcpy is the correct thing to use in your case.
Regards
Richard
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