Alignment Problem With Double On Sparc

Zhang, Bo bzhang@convergentnet.com
Fri May 31 12:42:00 GMT 2002


Hello, all,

Lately I encountered a problem with GCC (gcc-3.0.3) on alignment of double 
(long long or UINT64) variables on Sparc (Solaris 8). The following is a
brief 
description of the problem.

In our code, there are double variables which might not be 8-byte aligned
(nor the structures that contain these variables). In the non-optimized
code, 
the load/store of these variables are translated into two ld/st
instructions.
There is no problem. 

However, if I turn on -O2 option, the GCC compiler tries to use ldd/std 
(load/store of double) instructions for both the variables' assignments and 
copy of structures containing double variables. Because ldd/std expects
8-byte aligned addresses, it generates BUS_ERROR at run-time.

I tried a few Sparc specific GCC options, such as

    -munaligned-doubles
    -mno-faster-structs

>From the manual, these two options seem the exact choices for GCC
NOT to assume alignment and NOT to use ldd/std, but they didn't work
at all.

Have anyone encounter this problem before? Is there a solution to this?
Basically, I'm looking for a way to still do -O2 optimization, but not to 
use ldd/std (i.e. for GCC not to assume 8-byte alignment on double
variables and structures that contain them).

Any help is appreciated. Thanks.

Bo
>  



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