Re: [PATCH v4 00/13] port C-SKY to glibc

[Mao Han <han_mao at c-sky dot com>]

On Wed, Sep 12, 2018 at 12:31:24PM +0000, Joseph Myers wrote:
> On Wed, 12 Sep 2018, Mao Han wrote:
> 
> > 38245425a9add7bd22f8732219e0085432f223b6 (6 sep). Two abi combinations
> > are supported with this patch: C-SKY ABIV2 with (soft float & little endian,
> > hard float & little endian). CK807(ef), CK810(ef), CK860 are the
> 
> Could you please clarify whether those are the same ABI (compatible for 
> function calling, structure layout for types from glibc headers, etc.) or 
> different ABIs?
>
> If they are different ABIs, they should have different dynamic linker 
> names (of course you need to make the GCC port reflect the dynamic linker 
> name used for each ABI), and your bits/fenv.h should disable most of its 
> contents for soft float, like e.g. MIPS does (define only __FE_UNDEFINED 
> and FE_TONEAREST as rounding modes in that case, define FE_ALL_EXCEPT to 0 
> and no other exception macros, do not define FE_NOMASK_ENV).  Then you 
> shouldn't need math-tests-exceptions.h and math-tests-rounding.h in the 
> nofpu directory because things will be handled automatically when 
> bits/fenv.h avoids defining unsupported things.
> 
> If they are the same ABI, I don't see any use for the CSKY_HARD_FLOAT 
> macro defined in preconfigure; nothing seems to test it, so it's only 
> relevant if shlib-versions is testing it (i.e. if they are different ABIs 
> with different dynamic linker names).

Hard float will use to vr to pass arguments, the ABI is imcompatible if the
function has any float-point arguments. I use the same dynamic linker names
because there is no float in ldso, the same ldso can be used on system with
soft float/hard float. Seems I still need to use different dynamic linker
names even if they are compatible, and distinct soft float/hard float in
bits/fenv.h to make glibc have correct definitions?
> 
> Does C-SKY hard float support exception traps or not?  math-tests-trap.h 
> has a comment saying not.  But you have an implementation of 
> feenableexcept that implies it does support exception traps.
> 
> * If exception traps are never supported, everything related to them 
> (including the definition of FE_NOMASK_ENV) should be removed; the default 
> feenableexcept and fedisableexcept and fegetexcept implementations should 
> suffice.
> 
> * If exception traps are always supported, your math-tests-trap.h is wrong 
> and should be removed.
> 
> * If they are conditionally supported, like on Arm and AArch64, your 
> math-tests-trap.h is appropriate with a different comment explaining the 
> conditional support - but various fenv.h functions like feenableexcept 
> need to check for the support and give errors if asked to enable 
> exception traps they are unable to enable (this includes fesetenv and 
> feupdateenv passed FE_NOMASK_ENV - see Arm and AArch64 for examples).
>

Exception traps is design to be conditionally supported, seems define to no
for compatibility. All the cpu with fpu have exception traps support at
present and I have no method to check whether hardware support that, so I
prefer to remove math-tests-trap.h.

> > Several patches will be post to GCC and Binutils to fix some testcase fail
> > later this month, while the follow results have these patches applied.
> 
> Note that glibc ports can't go in while they depend on such non-upstream 
> patches for good results (see the ARC port discussion).  You can send a 
> list of all the patches required to get the given test results, but 
> they'll need to be upstream (as will the Linux kernel port) before the 
> port can go into glibc.
>

I can understand the glibc patch and test-result should base on upstreamed
gcc/binutils/linux. The purpose for this submission is to make sure there
is no big issue in this patchset itself. Once other components are ready
I can test the patch again and resubmit it easily.
I'v got another issue while using build-many-glibcs.py. 
csky-linux-gnuabiv2-gcc can not recognise -profile during the make check
stage and stoped. but it can recognise --profile. Is this a problem will
block the c-sky glibc port goes in.
 
> > 5. The following cases fail due to gcc optimize change the sequence of
> >    -a * b to -(a * b) and got 1ulps error.
> >    math/test-double-tgamma
> >    math/test-float-tgamma
> >    math/test-float32-tgamma
> >    math/test-float32x-tgamma
> >    math/test-float64-tgamma
> >    math/test-ldouble-tgamma
> 
> So that needs a GCC bug fix (just like when the Arm and AArch64 ports of 
> GCC used to have such a bug).
>

We have this bug tracked internally. Also need to report a bug on gcc bugzilla? 

Thanks,
Han Mao