On Monday 25 September 2006 02:41, william_lei@xxxxxxxxxx wrote:
> Could someone tell me how to modify GCC as titled?because we have met
> problem while porting some middleware,which will generate some lw/sw
> instruction to unaligned address,so I would modify GCC to not generate
> lw/sw instructions for this pieces code.
I'm not exactly sure what problem you are facing but if I understand you
correctly and you have code that simply does misaligned accesses, you would
be better off fixing the code. The reason is that such unaligned accesses
would have to be emulated with bytewise access and combining/dissecting the
values accordingly, which hurts performance (processing and cache). Even when
run on x86 (where such accesses don't cause bus errors) this would be the
better choice, because even there these are emulated in hardware and only
cause hidden performance losses.
Other than that, I would rather filter the output of GCC, i.e. use -S (or what
it was) to generate assembler code and then replace the lw/sw instructions
via your $FAVOURITE_TEXTPROCESSING_TOOL in the affected files. Most other
software isn't that broken and would only suffer from such changes.
Thinking about it, I believe there is also a way (some __attribute__) to tell
GCC that some pointer is not aligned and it will then output suitable code
for unaligned accesses. This requires changes to the generated sourcecode
though, but would be a rather clean solution because it would work on other
platforms, too.
Just wondering, what middleware are you talking about?
Uli
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