Re: quetion for gcc on hpux

["dai yiyang" <daiyiyang@xxxxxxxxxxx>]

well , Tru64 can catch & handle unaligned access by OS itself . the 
unaligned access only cause a system warning , but the code can be running 
only with performance penalty . there is a command to turn off the 
unaligned access message by OS ( I can forgot the name ).

HPUX can not handle unaligned access by default , for me  , maybe use 
libunalign.so on IA64 is the best way .I really don't want to change the 
code .


Regards,
Yiyang

> From: Eljay Love-Jensen <eljay@xxxxxxxxx>
> To: dai yiyang <daiyiyang@xxxxxxxxxxx>, gcc@xxxxxxxxxxx, 
gcc-help@xxxxxxxxxxx
> Subject: Re: quetion for gcc on hpux
> Date: Wed, 23 Feb 2005 06:28:40 -0600
>
> Hi Dai,
>
> If you choose not to change the bad code that is causing a SIGBUS, I 
> believe you cannot use GCC since (as far as I am aware) GCC does not 
> provide a mechanism *IN THE COMPILE/LINK* to catch the SIGBUS signal 
> and do the byte-by-byte manipulation to complete the action.
>
> Such handling of a SIGBUS slows down the performance of the 
> application significantly.  If the SIGBUS is happening on a data 
> structure that is often used, such as in a tight loop, you can 
> expect to see a degradation of performance on the order of two or 
> three magnitudes.
>
> You could write your own SIGBUS handler (as such, in that sense, GCC 
> provide a mechanism -- i.e., the building blocks to do it yourself), 
> so you wouldn't have to change the rest of your code other than in 
> main to put in your SIGBUS handler, and the SIGBUS handler itself.
>
> My recommendation is to fix the bad code, not surround the 
> application with a inevitably inefficient SIGBUS handler that masks 
> bad programming*.
>
> * "bad" in the sense of "violates system architecture constraints".
>
> HTH,
> --Eljay
>
> PS:  I ran into the same issue on DEC Alpha Tru64 machines.

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