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Date: Fri, 19 Jun 2020 23:20:34 -0400
From: Rich Felker <dalias@...c.org>
To: sidneym@...eaurora.org
Cc: musl@...ts.openwall.com, 'Szabolcs Nagy' <nsz@...t70.net>
Subject: Re: Hexagon DSP support

On Fri, Jun 19, 2020 at 09:29:04PM -0500, sidneym@...eaurora.org wrote:
> 
> 
> > -----Original Message-----
> > From: Rich Felker <dalias@...c.org>
> > Sent: Friday, June 19, 2020 5:46 PM
> > To: sidneym@...eaurora.org
> > Cc: 'Szabolcs Nagy' <nsz@...t70.net>; musl@...ts.openwall.com
> > Subject: Re: [musl] Hexagon DSP support
> > 
> > On Fri, Jun 19, 2020 at 04:58:53PM -0500, sidneym@...eaurora.org wrote:
> > >
> > > > -----Original Message-----
> > > > From: Szabolcs Nagy <nsz@...t70.net>
> > > > Sent: Thursday, June 18, 2020 4:43 PM
> > > > To: sidneym@...eaurora.org
> > > > Cc: musl@...ts.openwall.com
> > > > Subject: Re: [musl] Hexagon DSP support
> > > >
> > > > * sidneym@...eaurora.org <sidneym@...eaurora.org> [2020-06-18
> > > > 11:37:05
> > > > -0500]:
> > > > > I attached the updated REPORT with warning output disabled, -w and
> > > > > -fno-rounding-math (See
> > > > > https://bugs.llvm.org/show_bug.cgi?id=45329)
> > > > > along with the patch.  I've rebased a couple of times without any
> > > > > conflicts and the git repo is here:
> > > > > https://github.com/quic/musl/tree/hexagon
> > > >
> > > > the fmal failures are a bit concerning:
> > > >
> > > > fmal should be a tail call to fma if long double has the same
> > > representation as
> > > > double. (can you please verify this? there should be a single branch
> > > instruction
> > > > in fmal)
> > > >
> > > > there are no fma failures with the same tests so fmal should work
> > > > fine
> > > too.
> > >
> > > In the case of fma the selected function comes from
> compiler-rt-builtins.
> > > It looks like since fmal calls fma within the context of the c-library
> > > the c-library's version is branched to.
> > 
> > Are you talking about how libc-test was built or how musl was built?
> > This kind of replacement is not valid in either place. musl is built with
> -
> > ffreestanding, and libc-test is expected to be built with -fno-builtin.
> > 
> The link order is the reason.  The clang driver places
> -lclang_rt.builtins-hexagon ahead of -lc and it happens that this library
> includes an implementation of fma.  I think fma is something that was
> introduced in error in compiler-rt.builtins because hexagon is the only arch
> that has it.

Yes, that's a bug. compiler-rt cannot define libc functions.

Rich

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