On 07/03/2018 02:51 PM, Don Cross wrote:
On Tue, Jul 3, 2018 at 12:40 PM Bruce Dubbs <bruce.du...@gmail.com
<mailto:bruce.du...@gmail.com>> wrote:
On 06/29/2018 07:32 PM, Don Cross wrote:
> I wasn't sure whether to send this to lfs-support or lfs-dev.
Since I'm
> not a developer on LFS, I guessed the former. Apologies if my
guess is
> unhelpful.
>
> I built LFS using jhalfs and the 8.2 version of the book on a
machine
> with an Intel G860 processor. The configure script for libffi
guessed
> wrong about the processor's capabilities, causing Python 3 to
crash with
> an invalid instruction exception.
>
> I fixed this by changing the jhalfs script 115_libffi to let gcc
> determine the architecture rather than the configure script itself:
>
> ./configure --prefix=/usr --disable-static --with-gcc-arch=native
In the libffi source directory, can you pelease tell us what the output
of ./config.guess
In my case it is x86_64-unknown-linux-gnu.
-- Bruce
Hi Bruce, I see the same thing:
don@neptune:/sources/libffi-3.2.1 $ ./config.guess
x86_64-unknown-linux-gnu
However, I believe the smoking gun is in the output of ./configure when
I leave out the --with-gcc-arch=native. If I diff the output of
./configure without that native option (bad.txt) against the output with
that option (good.txt) I get:
don@neptune:/sources/libffi-3.2.1 $ ./configure --prefix=/usr
--disable-static > bad.txt
don@neptune:/sources/libffi-3.2.1 $ ./configure --prefix=/usr
--disable-static --with-gcc-arch=native > good.txt
don@neptune:/sources/libffi-3.2.1 $ diff bad.txt good.txt
106,110c106,108
< checking for x86 cpuid 0 output... d:756e6547:6c65746e:49656e69
< checking for x86 cpuid 1 output... 206a7:2100800:d9ae3bf:bfebfbff
< checking whether C compiler accepts -march=corei7-avx... yes
< checking for gcc architecture flag... -march=corei7-avx
< checking whether C compiler accepts -O3 -fomit-frame-pointer
-fstrict-aliasing -ffast-math -march=corei7-avx... yes
---
> checking whether C compiler accepts -march=native... yes
> checking for gcc architecture flag... -march=native
> checking whether C compiler accepts -O3 -fomit-frame-pointer
-fstrict-aliasing -ffast-math -march=native... yes
I'm not sure how ./configure comes up with corei7-avx, but the Intel
G860 does not support Advanced Vector eXtension instructions.
I think --with-gcc-arch=native is going to give the vast number of LFS
builders the correct output. If they are cross-compiling, they are going
to have to go through the pain of figuring out the target architecture
settings anyway, so they will be no worse off.
Thanks, that helps. I'll continue my investigation. there is a lot
going on in LFS right now so I will be making multiple updates in the
next few days.
-- Bruce
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