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

Sergey Kubushyn
2016-03-24T18:43:42Z

On Thu, 24 Mar 2016, Sergey Kubushyn wrote:

> On Thu, 24 Mar 2016, Marek Vasut wrote:
>
>> On 03/24/2016 12:54 AM, Sergey Kubushyn wrote:
>> > On Thu, 24 Mar 2016, Marek Vasut wrote:
>> >
>> > > On 03/24/2016 12:47 AM, Sergey Kubushyn wrote:
>> > > > On Thu, 24 Mar 2016, Marek Vasut wrote:
>> > > >
>> > > > > On 03/24/2016 12:08 AM, Tom Rini wrote:
>> > > > > > 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?
>> > > > >
>> > > > > I haven't seen the _udivmoddi4 emitted in my tests. Linux's libgcc
>> > > > > copy
>> > > > > also doesn't implement the function. Which toolchain do you use
>> > > > > and
>> > > > > which target did you compile?
>> > > >
>> > > > I'm using my own armv7hl-linux-gnueabi toolchain built for hard
>> > > > float.
>> > > > Linux
>> > > > arm libgcc does have arch/arm/lib/div64.S file that provides
>> > > > __do_div64()
>> > > > function that is used by do_div() from include/asm/div64.h for
>> > > > 32-bit
>> > > > ARM
>> > > > platform. Sure, arm64 has neither div64.h nor div64.S. We _DO_ have
>> > > > div64.h
>> > > > (that is totally different from what Linux provides) but no div64.S
>> > > > in
>> > > > arch/arm/lib.
>> > >
>> > > In that case, we should just import div64.S from Linux on arm32 and be
>> > > done with it ? Since we now have all the necessary macros thanks to
>> > > the
>> > > first four patches in this series, that should be trivial.
>> > >
>> > > What do you think? I can bake a patch real quick, so you can test it ?
>> >
>> > Sure I'll test it, no problems. Just bake the patch :)
>>
>> Done, give it a go please.
>
> OK, it didn't work, _udivmoddi4.o is still being pulled from libgcc. I'm
> analyzing it right now, will come up with more later today.

OK, it requires a CONFIG_USE_PRIVATE_LIBGCC defined to use private libgcc,
my bad -- thought it would be automatic. Having that defined makes build
fail complaining about assembly syntax in div64.S:

=== Cut ===
arch/arm/lib/div64.S: Assembler messages:
arch/arm/lib/div64.S:185: Error: bad instruction `arm( orr r2,r2,r1,lsl ip)'
arch/arm/lib/div64.S:186: Error: bad instruction `thumb( lsl r1,r1,ip)'
arch/arm/lib/div64.S:187: Error: bad instruction `thumb( orr r2,r2,r1)'
scripts/Makefile.build:316: recipe for target 'arch/arm/lib/div64.o' failed
make[1]: *** [arch/arm/lib/div64.o] Error 1
Makefile:1214: recipe for target 'arch/arm/lib' failed
make: *** [arch/arm/lib] Error 2
=== Cut ===

Probably something is missing in div64.h? The Linux one is totally
different. Digging in right now...

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