[Mingw-w64-public] Position independent code (-fPIC) on x86_64 Windows dll specially for Cygwin

[dashesy]

Reading the Wikipedia page
(http://en.wikipedia.org/wiki/Position-independent_code) , it seems
Windows supports PIC on x64,
Please correct me if I am wrong.
I was wondering if I can build PIC dlls on x64.
This would be specially useful with "--enable-cygwin" to eliminate the
need to do rebaseall at least on x64 platform and avoid the fork
failures.

Thanks
dashesy

[Kai Tietz]

Post by dashesy
Reading the Wikipedia page
(http://en.wikipedia.org/wiki/Position-independent_code) , it seems
Windows supports PIC on x64,
Please correct me if I am wrong.
I was wondering if I can build PIC dlls on x64.
This would be specially useful with "--enable-cygwin" to eliminate the
need to do rebaseall at least on x64 platform and avoid the fork
failures.
Thanks
dashesy

Well, you are right that x64 allows PIC in gcc. But you have to be
aware that even cygwin, and 32-bit native Windows images are *position
independent*. Just in comparison to ELF the Windows PE(+)-COFF
format is always a finally linked image. So PIC has here a different
meaning, as shared objects are pretty different.

Hope this helps,
Kai

[dashesy]

Post by Kai Tietz

Post by dashesy
Reading the Wikipedia page
(http://en.wikipedia.org/wiki/Position-independent_code) , it seems
Windows supports PIC on x64,
Please correct me if I am wrong.
I was wondering if I can build PIC dlls on x64.
This would be specially useful with "--enable-cygwin" to eliminate the
need to do rebaseall at least on x64 platform and avoid the fork
failures.
Thanks
dashesy

Well, you are right that x64 allows PIC in gcc. But you have to be
aware that even cygwin, and 32-bit native Windows images are *position
independent*. Just in comparison to ELF the Windows PE(+)-COFF
format is always a finally linked image. So PIC has here a different
meaning, as shared objects are pretty different.
Hope this helps,
Kai
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Thanks for the answer; is there any reference that I can read further?
I do not understand if they are position independent why loader might
rebase them on load.

BTW, this is the line in Wikipedia "64-bit Windows has switched to
using position-independent code for DLLs as well and has abandoned
relocation"
And it references here: http://msdn.microsoft.com/en-us/magazine/bb985017.aspx

Thanks again
dashesy

[Earnie Boyd]

Post by dashesy
BTW, this is the line in Wikipedia "64-bit Windows has switched to
using position-independent code for DLLs as well and has abandoned
relocation"
And it references here: http://msdn.microsoft.com/en-us/magazine/bb985017.aspx

For 64 bit binaries. Not for 32 bit binaries running in the emulator.
But does binutils support it for 64 bit binaries?

[dashesy]

On Wed, Aug 8, 2012 at 11:37 AM, Earnie Boyd

Post by Earnie Boyd

Post by dashesy
BTW, this is the line in Wikipedia "64-bit Windows has switched to
using position-independent code for DLLs as well and has abandoned
relocation"
And it references here: http://msdn.microsoft.com/en-us/magazine/bb985017.aspx

For 64 bit binaries. Not for 32 bit binaries running in the emulator.
But does binutils support it for 64 bit binaries?

That is the better way of asking my question.
Does binutils support it for 64-bit binaries, if yes it might give
-fPIC a new meaning (no longer a warning)

Post by Earnie Boyd
--
Earnie
-- https://sites.google.com/site/earnieboyd
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Thanks
dashesy

[Kai Tietz]

Post by dashesy
On Wed, Aug 8, 2012 at 11:37 AM, Earnie Boyd

Post by Earnie Boyd

Post by dashesy
BTW, this is the line in Wikipedia "64-bit Windows has switched to
using position-independent code for DLLs as well and has abandoned
relocation"
And it references here: http://msdn.microsoft.com/en-us/magazine/bb985017.aspx

For 64 bit binaries. Not for 32 bit binaries running in the emulator.
But does binutils support it for 64 bit binaries?

That is the better way of asking my question.
Does binutils support it for 64-bit binaries, if yes it might give
-fPIC a new meaning (no longer a warning)

Sure, x64 has PC-relocations. If binutils wouldn't support
PC-relative relocations we wouldn't have x64 support at all.
Sorry, I don't get the meaning here. Nevertheless PE-COFF might
have base-relocations even for 64-bit. But those are handled by
loader. To avoid these complete you need to avoid some
language-constructs, nevertheless the IAT tables are aways fixed-bound
to a specific address of imported module. If you have further
question about how PE(+)-COFF works, I recomment that you read the
pe-coff specification, which can be found on msdn for download.

Regards,
Kai