[OE-core] Yocto development with C++11 threads and gcc
Peter A. Bigot
pab at pabigot.com
Thu Aug 14 01:55:08 UTC 2014
On 08/13/2014 07:49 PM, Khem Raj wrote:
>
>
> On Wednesday, August 13, 2014, Peter A. Bigot <pab at pabigot.com
> <mailto:pab at pabigot.com>> wrote:
>
> On 08/13/2014 05:05 PM, Khem Raj wrote:
>
> On Wed, Aug 13, 2014 at 2:36 PM, Peter A. Bigot
> <pab at pabigot.com> wrote:
>
> In any case, Khem can you run with this? It'd be fixed a
> lot better that
> way....
>
> We do not configure target gcc with right matching cpu defaults,
> atomic instruction strex/ldrex are only added after armv6 but
> defaults
> for gcc if not specified is armv5t and hence it does not use
> the right
> set as expected by libstdc++ which has been cross compiled. so
> while
> you are at it and can reproduce it. Try to add
>
> EXTRA_OECONF += '${@bb.utils.contains("TUNE_FEATURES", "armv7a", "
> --with-cpu=armv7-a", "", d)}'
>
> to gcc-target.inc and see if resulting gcc is any better
>
>
> I had to make it:
>
> EXTRA_OECONF += '${@bb.utils.contains("TUNE_FEATURES", "armv7a",
> "--with-cpu=generic-armv7-a", "", d)}'
>
>
> Sorry a typo there you need --with-arch
OK, that works. So do we need to do the same thing for every
TUNE_FEATURES element that ends up changing the value of -march= in
TUNE_CCARGS which ends up getting passed into gcc-runtime?
If so would it be better to add a TUNE_ARCH setting to all the
tune-foo.inc files and use that in both TUNE_CCARGS and the --with-arch=
flag passed to gcc? Just to avoid having this stuff hidden inside
gcc-target.inc where it's pretty obscure.
>
> to get gcc to build but at runtime I then get:
>
>
> beaglebone[16]$ g++ -std=c++11 -pthread test.cc && ./a.out
> Assembler messages:
> Error: unknown cpu `generic-armv7-a'
> Error: unrecognized option -mcpu=generic-armv7-a
>
> which indicates the flag's being passed to the assembler which
> doesn't recognize it even though g++ is happy with it. I suppose
> we could hack binutils to substitute whatever spelling it wants to
> see.
>
> (Also tried --with-cpu=arm7, but that generates assembler errors
> related to unsupported RM mode "bx lr").
>
> The approach bothers me, though. Instead of explicitly changing
> gcc-target to match gcc-runtime, shouldn't it be a general rule
> that gcc-runtime not apply OE-specific target flags that aren't
> going to be used by direct invocations of the compiler outside of
> the OE build environment? That seems a little more robust, as the
> default target flags may be changed upstream or by bbappends
> within OE, and having to make them match in gcc-runtime as well
> would be a headache.
>
Just to record one reason why this isn't trivial: although it's possible
to strip ${TARGET_CC_ARCH} from ${CXX}, doing so removes
-mfloat-abi=hard which makes gcc-runtime try to build a library that
supports soft float, and the compiler didn't generate the necessary
gnu/stubs-soft.h header for that.
>
> And would we need similar overrides for other architectures?
> There's something similar already in gcc-configure-common.inc for
> mips64.
>
> Peter
>
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