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Re: [avr-libc-dev] [RFC] Patch adding support for atmega2560-2561

From: Björn Haase
Subject: Re: [avr-libc-dev] [RFC] Patch adding support for atmega2560-2561
Date: Mon, 19 Sep 2005 10:34:41 +0200
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David Brown wrote on Montag, 19. September 2005 09:53 :
> I'm not too hot on the internals of gcc, but I'm wondering if there is not
> already a mechanism in place for gcc to detect purely internal linkage (by
> which I mean a "static" function whose address is never taken).  When a
> function is declared "inline", the compiler has to know whether it must
> also generate an "outline" version as well - if it knows the function is
> "static" and the address is never taken, the "outline" version is not
> generated. Could this also be used to determine if a stub is needed or not?
>  If this were possible, then the stub could be avoided by simply declaring
> functions to be "static" if they are not needed externally to the file,
> cutting down the overhead substantially, since the majority of functions
> can be labelled "static".  Of course, that requires a bit of discipline on
> the part of the programmer, as they would have to use "static" explicitly
> on all non-extern functions.  But that's good practice anyway (and easily
> checked with "-Wmissing-prototypes" ).
Maybe. I however don't know right now how to do that right now. I rather have 
looked for a *easy to implement and safe* method. For this reason, e.g., I 
also did not implement the jump stubs as RTL but rather as text.
> An alternative idea might be to use individual sections such as
> ".text1_foo" for the stub for function foo(), and make use of the
> "--gc-sections" option in the linker to remove any such section that is not
> used.  
> I'm thinking of the same idea as the "-ffunction-sections" switch in 
> gcc which can be used with "--gc-sections" to avoid linking in functions
> that are not used.  I haven't tried the "-ffunction-sections" switch, and
> don't even know if it is implemented for the avr port, but perhaps the same
> idea can be used.
If the -ffunction-sections is functional, this would probably be the easiest 
and best approach.

BTW, I just recognized that one probably will also need to disable or modify 
the table jump insn patterns.


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