[U-Boot] [PATCH 5/5] lib: Enable private libgcc by default

Tom Rini
2016-03-23T23:08:34Z

On Wed, Mar 23, 2016 at 04:02:07PM -0700, Sergey Kubushyn wrote:
> On Wed, 23 Mar 2016, Tom Rini wrote:
>
> >On Wed, Mar 23, 2016 at 06:08:45PM +0100, Albert ARIBAUD wrote:
> >>Hello Tom,
> >>
> >>On Wed, 23 Mar 2016 09:22:38 -0400, Tom Rini <trini@konsulko.com> wrote:
> >>>On Wed, Mar 23, 2016 at 01:53:35PM +0100, Albert ARIBAUD wrote:
> >>>>Hello Marek,
> >>>>
> >>>>On Sun, 20 Mar 2016 17:15:34 +0100, Marek Vasut <marex@denx.de> wrote:
> >>>>>This patch decouples U-Boot binary from the toolchain on systems where
> >>>>>private libgcc is available. Instead of pulling in functions provided
> >>>>>by the libgcc from the toolchain, U-Boot will use it's own set of libgcc
> >>>>>functions. These functions are usually imported from Linux kernel, which
> >>>>>also uses it's own libgcc functions instead of the ones provided by the
> >>>>>toolchain.
> >>>>>
> >>>>>This patch solves a rather common problem. The toolchain can usually
> >>>>>generate code for many variants of target architecture and often even
> >>>>>different endianness. The libgcc on the other hand is usually compiled
> >>>>>for one particular configuration and the functions provided by it may
> >>>>>or may not be suited for use in U-Boot. This can manifest in two ways,
> >>>>>either the U-Boot fails to compile altogether and linker will complain
> >>>>>or, in the much worse case, the resulting U-Boot will build, but will
> >>>>>misbehave in very subtle and hard to debug ways.
> >>>>
> >>>>I don't think using private libgcc by default is a good idea.
> >>>>
> >>>>U-Boot's private libgcc is not a feature of U-Boot, but a fix for some
> >>>>cases where a target cannot properly link with the libgcc provided by
> >>>>the (specific release of the) GCC toolchain in use. Using private libgcc
> >>>>to other cases than these does not fix or improve anything; those
> >>>>other cases were working and did not require any fix in this respect.
> >>>
> >>>This isn't true, exactly. If using clang for example everyone needs to
> >>>enable this code. We're also using -fno-builtin -ffreestanding which
> >>>should limit the amount of interference from the toolchain. And we get
> >>>that.
> >>
> >>You mean clang does not produce self-sustained binaries?
> >
> >clang does not provide "libgcc", so there's no -lgcc providing all of
> >the functions that are (today) in:
> >_ashldi3.S _ashrdi3.S _divsi3.S _lshrdi3.S _modsi3.S _udivsi3.S
> >_umodsi3.S div0.S _uldivmod.S
> >which aside from __modsi3 and __umodsi3 are all __aeabi_xxx
>
> There is also _udivmoddi4 pulled from libgcc for 64-bit division since we
> switched to 64-bit all around ARM. It comes from clock calculations for
> video, e.g. from drivers/video/ipu_common.c for i.MX6.

Well, this is an example of why we both don't want libgcc ever nor do we
want to overly expand what we do offer. In this case isn't it an
example of something that should be using lldiv/do_div/etc?

--
Tom
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