On 10/4/12 3:36 PM, Khem Raj wrote:
On Thu, Oct 4, 2012 at 11:02 AM, Mark Hatle <[email protected]> wrote:
We have an issue where we'd like to have an alternative toolchain
(assembler, linker, compiler) available for our customers to selectively
use. However, before we just go off and implement something, I'd like at
least some basic consensus on what the best practice is for doing this work.
Below is my attempt at an early proposal.
Background
----------------
Many companies have commercial / highly optimized toolchains for specific
purpose, such as ICC from Intel, LLVM, ARM specific toolchain, etc.. For
(potentially) better performance with some applications a mechanism to both
provide the hooks for the alternative toolchain as well as a way to active
it per-package is desired.
This work assumes that the third party toolchain is generally compatible
with the idea of sysroots, linking to the libc provided by OE, and generally
compatible with GNU conventions.
However, as part of the third party toolchain, it may not be GNU compatible.
This means many Open Source applications simply may not work with this
toolchain. That means that we need to have a way for a toolchain to
blacklist (or whitelist) specific recipes. This way only supported
components can be built by the user, avoiding numerous complaints.
Currently OE has a method to generate an SDK based on the GNU toolchain. We
would like to be able to also export the external toolchain along with the
SDK, effectively providing both the GNU toolchain and the third party
toolchain using the common sysroot.
We need a way to active the third party toolchain on a per-package basis.
Per package bases is a bit iffy from my POV if you consider the compiler runtime
and C library runtime and so forth. Is it intended to just compile and
be able to
cope with the default runtimes on images or do you also intend to figure out
ways for multiple runtimes to live together.
This is only one runtime. You have multiple compilers all capable of producing
software compatible with the same ABI. The default (oe) compiler is used,
unless otherwise configured. The alternative(s) are used for optimization of
various items. I mentioned ICC, because it's one that I know today people are
using and it is capable of replacing gcc in many applications.
The issue is that I want to enable someone to use an alternative compiler, but I
don't want to do anything beyond enabling it if it doesn't work.
This activation will need to use the existing sysroot, but be able to pass
different C, C++, LD, AS and other flags as specified by the third party
toolchain.
that sort of answers the above. So we are assuming that toolchain that
can interoperate
will be using GNU runtime
There are cases where you might want something like ELLCC which avoids
complete GPL runtime e.g.
I think it could be divided into runtime + tools where runtime lives
in a different layer but
essentially offering to let people use builtin C library and runtime
may not be a bad choice
When the runtime changes, I consider that to be a different abi and outside the
scope of this. Thats where the machine/multilib/etc configuration items come
into play. (I.e. some architectures support an alternative compiler for bare
metal applications -- in those cases the canonical arch is no longer
-linux[-gnu]... so they would simply be treated as a different architecture.)
Finally third party toolchains should be implemented as layers that can
easily plug into OE.
agreed. I think we need to document the interfaces in OE-Core for this
too so that
people can rely on the interface. Otherwise it will be constant pain
for keeping those
layers working together.
Exactly.. I don't want people coming to me saying I want XYZ compiler, but it's
implemented for my semi-conduction specific Linux and won't work with your OSV
based Linux. That doesn't help anyone (unless they are intentionally trying to
be incompatible!) So if we can provide a functional best practice and example
of how to do this, then when people want to provide (and use) a secondary
toolchain -- it's available to them.
Implementation
---------------------
Add an OVERRIDE to specify the alternative toolchain. Can this be done
within the layer by doing something like:
OVERRIDE_append = ":toolchain-${TOOLCHAIN}"
TOOLCHAIN = "gnu" (or "icc")
To activate the toolchain you would use things like:
TOOLCHAIN_pn-bash = 'icc'
To define the correct behavior for the toolchain, the following would need
to be defined (with _toolchain-<toolchain>):
TARGET_CPPFLAGS
TARGET_CFLAGS
TARGET_CXXFLAGS
TARGET_LDFLAGS
CC
CXX
F77
CPP
LD
CCLD
AR
AS
RANLIB
STRIP
OBJCOPY
OBJDUMP
NM
FULL_OPTIMIZATIONS
DEBUG_OPTIMIZATION
Is anyone aware of any other items that may require additional items? Will
the above actually work? Using the override of the TOOLCHAIN_… will that
actually change the override values or do we get stuck?
Comments/suggestions appreciated!
--Mark
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