| Title: | DECWINDOWS 26-JAN-89 to 29-NOV-90 |
| Notice: | See 1639.0 for VMS V5.3 kit; 2043.0 for 5.4 IFT kit |
| Moderator: | STAR::VATNE |
| Created: | Mon Oct 30 1989 |
| Last Modified: | Mon Dec 31 1990 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 3726 |
| Total number of notes: | 19516 |
I'm porting some code onto MIPS/ULTRIX that I know works on both
platforms on VAX.
I'm getting a series of messages like:
Fixed up unaligned data access for pid 18599 (demo) at pc 0x480440
I'm told the primary cause of this is structure members allocated
on uneven word boundaries. However I've checked all my structures
and they only have 32-bit members (ints and char *'s).
I also tracked some of the messages as far as I could using dbx, and
they're being issued while DECwindows toolkit code is being executed.
Specifically, inside a subroutine of DwtDrmHGetIndexedLiteral. I
also call this routine elsewhere in my code, and that's okay.
Can anyone give me any suggestions, or even shed light on whether
it's still likely to me me rather than the toolkit that's causing
the messages ?
Thanks,
Dave
BTW. The program still works fine, it just issues ugly (and worrying)
messages.
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 798.1 | FLUME::dike | Thu May 18 1989 10:04 | 8 | ||
I have seen unaligned accesses when a caller and callee disagree about the size of a parameter, for example, I saw this when calling XTranslateCoordinates with pointers to shorts instead of pointers to ints. However, the only parameter that seems suspicious in your case is the context_id and I don't know enough to say whether that could be the cause. Jeff | |||||
| 798.2 | More confused now | 45830::CURLEY | Dave Curley, IED/Reading, DTN 830-4354 | Thu May 18 1989 11:13 | 13 |
Jeff,
I don't understand...
Aren't pointers the same size regardless of whether they
point to ints or shorts ? Or am I being silly ?
I just ran a program on MIPS to print sizeof() for an int *,
and for a short *, and got 4 for both.
Dave
| |||||
| 798.3 | Why not a toolkit problem? | TLE::D_SMITH | Thu May 18 1989 12:21 | 8 | |
Isn't it possible that the resource manager has a structure which does
not have fields on "natural" boundaries? I just had a look at one of
the DRM include files from around last June and one of the structures
was declared with a short int followed by a character pointer. If I
understand the data types correctly a short int is 16 bits while a
character pointer is 32. This would result in the address fixup.
Perhaps one of the toolkit people should have a look.
| |||||
| 798.4 | Its not a toolkit problem. | 56579::thomas | The Code Warrior | Thu May 18 1989 12:31 | 28 |
The most common way of getting unaligned access errors is Calling DwtGetNextSegment with a dirRtoL declared as a boolean. The routine itself declares dirRtoL as a int *. Having pointer dereferences like *(int *)p (where int could be short or a struct tag * as well) and p is char *. To find out where it is happening, use dbx. For instance: Fixed up aligned access for pid 1110 (hpwm) at pc 0x44b820. % dbx hpwm [...] (dbx) 0x44b810/10i [XQueryPointer:176, 0x44b810] lw r14,96(sp) [XQueryPointer:176, 0x44b814] lh r13,60(sp) [XQueryPointer:176, 0x44b818] nop [XQueryPointer:176, 0x44b81c] sw r13,0(r14) [XQueryPointer:184, 0x44b820] lw r24,100(sp) [XQueryPointer:184, 0x44b824] lh r15,62(sp) [XQueryPointer:184, 0x44b828] nop [XQueryPointer:184, 0x44b82c] sw r15,0(r24) [XQueryPointer:192, 0x44b830] lw r8,104(sp) [XQueryPointer:192, 0x44b834] lhu r25,64(sp) So obviously hpwm has a problem calling XQueryPointer. | |||||
| 798.5 | But that suggests the toolkit | 45830::CURLEY | Dave Curley, IED/Reading, DTN 830-4354 | Thu May 18 1989 13:18 | 19 |
Ok, I did that to track down the source of the problem originally,
and the subroutine I mentioned in .0 is what I arrived at.
Here's my version of the dbx dump, but I'm still unclear on whether
it's MY fault or not, as I'm not passing any strange arguments:
[DwtIdb__DB_GetDataEntry:198, 0x48b700] addiu r17,r17,16
[DwtIdb__DB_GetDataEntry:189, 0x48b704] ori r21,r21,0x88ae
[DwtIdb__DB_GetDataEntry:199, 0x48b708] beq r8,r21,0x48b748
[DwtIdb__DB_GetDataEntry:199, 0x48b70c] nop
[DwtIdb__DB_GetDataEntry:202, 0x48b710] lui r4,0x1002
[DwtIdb__DB_GetDataEntry:202, 0x48b714] lui r5,0x1002
[DwtIdb__DB_GetDataEntry:202, 0x48b718] li r9,26
[DwtIdb__DB_GetDataEntry:202, 0x48b71c] sw r9,16(sp)
[DwtIdb__DB_GetDataEntry:202, 0x48b720] addiu r5,r5,21328
[DwtIdb__DB_GetDataEntry:202, 0x48b724] addiu r4,r4,21304
Dave
| |||||
| 798.6 | What the address of the unaligned access? | 56579::thomas | The Code Warrior | Thu May 18 1989 16:08 | 2 |
Looking at the routine, it might be possible but it doesn't look probable. | |||||