Re: how to solve a non pic code in an shlib due to assembly code

[Goswin von Brederlow <goswin-v-b@web.de>]

Ove Kaaven <ovek@arcticnet.no> writes:

> Goswin von Brederlow skrev:
>> Ove Kaaven <ovek@arcticnet.no> writes:
>> 
>>> However, if they can't or won't fix it, there's *some* good news. In
>>> general, shared libraries must be compiled as PIC because on some
>>> platforms, the library just won't work properly if you don't. However,
>>> i386 and amd64 are not among those platforms. Since the MMX code is only
>>> compiled for those, it might be safe to ignore the lintian error in this
>>> particular case, if there's no other way.
>> 
>> Slight correction for the books. No insult intended. Amd64 is verry
>> much among those. You usualy end up with a 4 byte offset that is
>> computed at runtime link time. But with a shared library there is no
>> garanty that the offset will fit in 4 bytes and during compile time
>> the linker will complain about a 32bit offset being used where 64bit
>> might be needed. Sorry, don't know the exact error message by hard.
>
> I suppose I haven't used the amd64 instruction set enough yet (never had
> any excuse to do so yet). However, I've seen that, unlike i386, amd64
> does have a PC-relative addressing mode. I'd assume the assembler would
> usually use it to try to avoid these problems.

The assembler will do what you tell him too. :) You have to actually
use the right mode.

> Reviewing the documentation, you have a point in that you probably need
> to use amd64 addressing forms that allow this in order for the assembler
> to be able to do the right thing. Perhaps the C compiler generally don't
> if you don't use -fPIC. But the asm code used here seems to only use
> constant displacements when loading memory addresses, which means the
> assembler should be able to emit PC-relative addresses automatically, if
> it knows what's good for it. And this *should* also go for any other
> well-written amd64 asm code out there (even if written for Windows).
>
> And so my excuse is that I was only concerned about the asm code...

Yes, without -fPIC the compiler will use the wrong mode, a 32bit
offset.

But for asm it will use the mode you give it.

MfG
        Goswin