gcc has -march=native which uses the current CPU's architecture, but I
think it would be a really bad idea to turn that on by default, because
it would mean that we have to be really careful which machine we build
the distributions on.
On my Linux box, gcc -v says it was configured with --with-arch-32=i686,
which means that -march=i686 is the default for 32-bit code. We
shouldn't go any later than that IMO.
Anyway, this is all beside the point, if we aren't able to run the code
generated by gcc (in whatever mode) then there's a bug somewhere.
Cheers,
Simon
On 17/07/2014 07:39, Johan Tibell wrote:
Alright, then which Make file do we need to fix to make sure GCC is
called correctly? Also, I remember reading that some time during the
4.x GCC series GCC switched to auto-detecting the arch to be that of
the machine being used. Could someone try to just switch GCC to a
newer version and see if it automatically stops trying to use i386,
leading to Simon's problem?
On Thu, Jul 17, 2014 at 8:37 AM, Niklas Larsson <metanik...@gmail.com> wrote:
It certainly shouldn't be built with i386, because that is generating code
for a processor that lacks all these fancy atomic instructions. The first of
them appears on the 486.
i686 should be safe, it goes all the way back to Pentium Pro.
2014-07-17 8:33 GMT+02:00 Johan Tibell <johan.tib...@gmail.com>:
A perhaps silly question, *should* ghc-prim be built with i386 or i686?
On Thu, Jul 17, 2014 at 8:33 AM, Niklas Larsson <metanik...@gmail.com>
wrote:
I just found exactly the same thing! Well, I used i686 instead.
Sounds like it's worthwhile to see if this is limited to ghc-prim or if
there's more stuff that's built with i386.
2014-07-17 8:21 GMT+02:00 Páli Gábor János <pali.ga...@gmail.com>:
2014-07-17 0:51 GMT+02:00 Páli Gábor János <pali.ga...@gmail.com>:
2014-07-17 0:47 GMT+02:00 Niklas Larsson <metanik...@gmail.com>:
I hope they can just be done away with at the source, that is to
make
gcc
generate the assembly primitives. GHC should already be built with
i686, but
does that reach ghc-prim?
This depends on GCC -- if no -march=XXX is explicitly set, I guess it
will take its default, which may vary platform by platform.
All right, I have finally got a Windows (x64) machine and installed
the msys2 environment by the GHC wiki [1]. This has GCC 4.5.2 (as
Niklas wrote earlier), where the default -march is i386. You should
see this line when trying to compile Johan's test program with the -v
flag set:
COLLECT_GCC_OPTIONS= ... '-v' '-mtune=i386' '-march=i386'
With the -march=i586 flag explicitly set in the command line, no
__sync_fetch_and_add_n() calls are generated.
[1]
https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Windows/MSYS2
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