[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From rth at gcc dot gnu dot org 2005-01-04 09:14 --- Subject: Re: Unaligned access to fields inside packed records Could you tell on what grounds? AFAICS all fields are still addressable. Not really, they aren't. I've argued in the past that we should either make them non-addressable, or (more usefully) implement pointers to unaligned data. But having done neither, the result of the addressof operator is undefined. r~ -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From rth at gcc dot gnu dot org 2005-01-03 23:16 --- The Ada compiler may do it, but the C compiler does not. This test case, written in C, is invalid. -- What|Removed |Added Status|NEW |RESOLVED Resolution||INVALID http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From ebotcazou at gcc dot gnu dot org 2005-01-04 05:17 --- The Ada compiler may do it, but the C compiler does not. This test case, written in C, is invalid. Could you tell on what grounds? AFAICS all fields are still addressable. -- What|Removed |Added CC||rth at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From ebotcazou at gcc dot gnu dot org 2005-01-02 10:57 --- Reconfirmed with gcc version 4.0.0 20050101 (experimental) at -O0 on SPARC 32-bit. -- What|Removed |Added Status|UNCONFIRMED |NEW Ever Confirmed||1 Last reconfirmed|-00-00 00:00:00 |2005-01-02 10:57:40 date|| http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From ebotcazou at gcc dot gnu dot org 2005-01-02 11:03 --- Clobber_Hour_Of: save%sp, -112, %sp st %i0, [%fp+68] ld [%fp+68], %g1 add %g1, 5, %g1 mov %g1, %o0 callAssign_Hour_Of, 0 nop is wrong: you can't merely add 5 to the address on STRICT_ALIGNMENT platforms. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From ebotcazou at gcc dot gnu dot org 2005-01-02
11:11 ---
.t03.generic is already wrong:
Clobber_Hour_Of (dt)
{
struct Time_T * D.1122;
D.1122 = dt-Time;
Assign_Hour_Of (D.1122);
}
struct Time_T is 32-bit aligned so D.1122 must be a multiple of 4; as such, it
cannot be assigned dt-Time which is not a multiple of 4. A properly aligned
temporary should be created instead and its address assigned to D.1122.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From giovannibajo at libero dot it 2005-01-02 16:45 --- Are we really forced to support ADDR_EXPR on unaligned fields? How would you fix it with a temporary? Are you going to generate a FINALLY_EXPR to copy the contents of the temporary back into the original field? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From ebotcazou at gcc dot gnu dot org 2005-01-02 17:20 --- Are we really forced to support ADDR_EXPR on unaligned fields? How would you fix it with a temporary? Are you going to generate a FINALLY_EXPR to copy the contents of the temporary back into the original field? Yes and yes. The Ada compiler has been doing this for ages. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From wintermute101 at wp dot pl 2004-11-04 16:54 ---
I write here cause it's simmilar situation as reported here but I have no data
about other gcc versions than 3.3.2.
I have following:
/
define _aligned(n) __attribute__((aligned(n), packed))
struct CzazPort {
unsigned short number;
unsigned long speed;
unsigned long protocol;
unsigned long mode;
unsigned short timeout;
unsigned short loglevel;
unsigned short timerid;
} _aligned(2);
struct CzazPort tmp;
sscanf( data, %lu, tmp.speed );
/
data=9600
before sscanf (content of tmp)
00:01:00:00:96:00:52:54:55:00:38:4e:31:00:03:e8:00:04:2b:67
after sscanf
00:00:25:80:96:00:52:54:55:00:38:4e:31:00:03:e8:00:04:2b:67
9600 in hex - 0x2580
it was compiled for MOXA UC7420
the same program compiled for i686 works fine
this MOXA has XScale Intel prcessor working in big-endian. I guess this is the
problem (big-endian).
sscanf is just example from source. The same occurs when I relpace sscanf with
(*(tmp.speed)) = 9600;
but
tmp.speed=9600;
works fine.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From ebotcazou at gcc dot gnu dot org 2004-11-03 17:53 --- Created an attachment (id=7467) -- (http://gcc.gnu.org/bugzilla/attachment.cgi?id=7467action=view) Testcase. To be compiled with -O0. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From pinskia at gcc dot gnu dot org 2004-11-03 18:02
---
Are you sure that 4.0.0 does not work, as it no longer does the transformation for
(a-b) into a +
offsetof(a,b).
From the last tree dump for 4.0.0:
;; Function Assign_Hour_Of (Assign_Hour_Of)
Assign_Hour_Of (t)
{
bb 0:
t-Hour = 44;
return;
}
;; Function Clobber_Hour_Of (Clobber_Hour_Of)
Clobber_Hour_Of (dt)
{
struct Time_T * D.1128;
bb 0:
D.1128 = dt-Time;
Assign_Hour_Of (D.1128);
return;
}
;; Function main (main)
main ()
{
struct Date_And_Time_T dt;
int D.1135;
bb 0:
dt.Time.Hour = 22;
Clobber_Hour_Of (dt);
D.1135 = 0;
return D.1135;
}
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From pinskia at gcc dot gnu dot org 2004-11-03 18:03 --- t-Hour = 44; /* unaligned word access */ is unaligned word access if t is not word aligned in the first place, correct which is where the problem comes in right? -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From ebotcazou at gcc dot gnu dot org 2004-11-03 18:17 --- t-Hour = 44; /* unaligned word access */ is unaligned word access if t is not word aligned in the first place, correct which is where the problem comes in right? I confirm that the bus error (not bug error!) happens with 4.0.0 20041103. But, you're right, probably another problem there. The compiler should not pass the adress of dt-Time to Assign_Hour_Of if it can't prove that the field is at least as aligned as its type. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
[Bug c/18287] Unaligned access to fields inside packed records
--- Additional Comments From pinskia at gcc dot gnu dot org 2004-11-03 19:57 --- There is another example of this in PR 17949 where the tree-optimizations cause something werid to happen only because the middle-end does not know that they are unaligned loads. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18287
