Windows: -fPIC is added even platform is position independent

[luislavena]

Hello,

While attempting to cross-compile libsodium to Windows (from OSX using mingw-w64 GCC 4.5.4), I've encountered several warnings during compilation:

Making all in include
make[3]: Nothing to be done for `all'.
  CC       libsodium_la-core_hsalsa20.lo
crypto_core/hsalsa20/ref2/core_hsalsa20.c:1:0: warning: -fPIC ignored for target (all code is position independent)
  CC       libsodium_la-core_salsa20.lo
crypto_core/salsa20/ref/core_salsa20.c:1:0: warning: -fPIC ignored for target (all code is position independent)
  CC       libsodium_la-core_salsa2012.lo
crypto_core/salsa2012/ref/core_salsa2012.c:1:0: warning: -fPIC ignored for target (all code is position independent)
  CC       libsodium_la-core_salsa208.lo
crypto_core/salsa208/ref/core_salsa208.c:1:0: warning: -fPIC ignored for target (all code is position independent)

Perhaps -fPIC check done in configure.ac can evaluate the platform being targeted?

Environment information:

$ uname -v
Darwin Kernel Version 12.2.1: Thu Oct 18 12:13:47 PDT 2012; root:xnu-2050.20.9~1/RELEASE_X86_64

$ i686-w64-mingw32-gcc --version
i686-w64-mingw32-gcc (GCC) 4.5.4 20110822 (prerelease)

Cross-compiler was obtained from mingw-w64 project.

Thank you

❤️ ❤️ ❤️

[jedisct1]

This warning is really harmless, the compiler is actually saying "hey, I'm doing what you expected".
We definitely want the code to be position-independent. I don't know if this is the case by default for all versions of MingW and if it will always be the case.
Do you know of a reliable way with autoconf to detect if some compilation option spits out a warning? Or if there is a -Wno-* switch we could use?

[luislavena]

I don't know if this is the case by default for all versions of MingW and if it will always be the case.

http://en.wikipedia.org/wiki/Position-independent_code#Windows_DLLs

Do you know of a reliable way with autoconf to detect if some compilation option spits out a warning?

http://stackoverflow.com/a/4787225/117298

I think libtool is already aware of this?

[jedisct1]

libtool doesn't seem to be aware of this. Removing -fPIC from our configure.ac file causes libtool to re-add it no matter what.
I'll look at it later. This doesn't change the compiled code in any ways.