[Qbs] How to pass -march=armv7-a to the g++ linking command line (without -Wl, )

[Christian Gagneraud]

On 16 January 2018 at 17:00, Wookey <wookey at wookware.org> wrote:
> On 2018-01-16 12:08 +1300, Christian Gagneraud wrote:
>>
>> I found this piece of information very interesting indeed, what's your
>> stance about -march then? In my case, I have one toolchain per platform
>> (roughly), they all have the same generic triplet (arm-linux-gnueabi), but
>> target different ARM arch (armv5te, armv6, cortex A?, ...) and actually have
>> sometimes different float ABI.
>
> I think you are doing it wrong, in more than one way :-)

Easy answer: "they" are doing it wrong (the other team), and as a
consumer of their work i'm just trying to bring some consistency,
hence all my questions/comments.

> I like to distinguish between ISA (instruction set) and ABI
> (Application Binary Interface). An 'architecture' in Debian is
> actually an ABI (not a machine, nor a CPU). That never changes for the
> lifetime of the architecture. The ISA that arch is built with can
> change over time as newer hardware becomes a sensible default i386->
> i486 -> i686 in the i386-linux-gnu ABI, and armv4t -> armv5 -> armv7
> in the arm-linux-gnueabi ABI, for example.

<my-life>
My personal (p)references in term of ISA stability would be sparc and
ppc, but at work i have to deal with x86 32/64 and arm v5/6/7/8...
On top of that are desktop and custom embedded GNU/Linux,
Android/Linux, with a mix of gcc and clang as a final topping choice.
Not talking about sse, avx, neon, vfp, Qt's own qreal=float or double,
arm vs x86 char signed-ness, ...
</my-life>

I think that "how do you name a toolchain" is a legit question and the
old GNU triplet/quadruplet myth is, well, just a myth! ;)
I remember vaguely the "gnueabi" vs "oldabi" vs "" toolchain mess when
the hard-float call convention was introduced into the arm-linux
kernel ...

> Does that all make sense. Are we off-topic for this mailing list yet?

Yes it does, and Qbs aims to be OS/toolchain agnostic, so I don't
think this is fully off-topic.
IMHO, all these questions/answers fully makes sense on this ML.
Enlightenment and sanity are always welcome! ;)

Chris