[bug#49019] [PATCH 0/1] gnu: Add gccgo-10.

[Efraim Flashner]

On Mon, Jun 21, 2021 at 09:32:22PM +0000, iskarian@mgsn.dev wrote:
> Thanks for taking a look at this, Efraim!
> 
> June 21, 2021 6:25 AM, "Efraim Flashner" <efraim@flashner.co.il> wrote:
> 
> > On Sun, Jun 13, 2021 at 09:16:53PM -0700, Sarah Morgensen via Guix-patches 
> > via wrote:
> > 
> >> The primary goal for adding gccgo is to bootstrap the go compiler for 
> >> arches
> >> that aren't supported by go 1.4. I believe the major one to support here is
> >> powerpc64le, but I am unsure of current arch usage. A secondary goal is to
> >> provide a gccgo-toolchain, as gccgo may provide advantages over gc in time.
> >> 
> >> I have successfully built gccgo 9, 10 and 11 for x86-64. I additionally 
> >> tested
> >> gcc 10 using `make check-go`. There are two minor test failures:
> >> 
> >> 1. index0-out.go, previously reported upstream [0]
> >> 2. pprof (TestConvertCPUProfile/TestConvertMemProfile)
> >> 
> >> (I have not yet been able to deterine whether the pprof failures are an 
> >> upstream
> >> bug or a Guix bug. Should I send details to bug-guix?)
> > 
> > I wouldn't worry about the test failures.
> > 
> >> Finally, the regex update in [1] is implemented in CUSTOM-GCC-GCCGO rather 
> >> than
> >> CUSTOM-GCC to avoid rebuilding 2k+ gfortran packages, and CUSTOM-GCC-GCCGO
> >> should be removed after the change is in master.
> > 
> > Makes sense
> > 
> >> [0] https://issues.guix.gnu.org/49010
> >> [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87589
> >> 
> >> Sarah Morgensen (1):
> >> gnu: Add gccgo-10.
> >> 
> >> gnu/packages/gcc.scm | 77 ++++++++++++++++++++++++++++++++++++++++++++
> >> 1 file changed, 77 insertions(+)
> >> 
> >> --
> >> 2.31.1
> > 
> > I threw together a quick gccgo-toolchain package and tried using that to
> > build keybase and syncthing. One of the errors I came across was:
> > /home/efraim/go/pkg/mod/golang.org/x/sys@v0.0.0-20200922070232-aee5d888a860/unix/gccgo.go:50:
> > undefined reference to `gccgoRealSyscallNoError' and also
> > github.com/minio/sha256-simd@v0.1.1 didn't like the assembly in the
> > package.
> 
> The assembly problem is (unfortunately) a known limitation of gccgo. The gc 
> and
> gccgo compilers use different asm syntax, so many extant go programs cannot
> currently be compiled with gccgo alone. There are also other limitations with
> the go tools provided by gccgo, as only a subset have been implemented.
> 
> However, I have successfully built go-1.16 with gccgo with a few tweaks. (Most
> dependent packages build with no modification or with a version bump, and I
> have minimal patches for the handful of others. Docker will have to be updated
> to work with go-1.16, which will likely be out of my depth.) I plan to share
> a patchset for this soon.
> 
> As for x/sys: most likely updating the module dependency will solve it. I see
> x/sys has had some gccgo related commits since that version was released.

Sounds good.

> > It's definitely possible that I'm missing some flag to tell go that I'm
> > really using gccgo. Or that it should be built with binutils-gold.
> 
> I must admit that I had not even thought about whether gold might be
> necessary. I really am out of my depth on this one. I see that you authored
> the patch for go@1.14 to use gold on armhf and aarch64, so you likely know
> more about this than me! Presumably that was in regards to [0] and [1]?

That one's come forward with a couple of go versions. Perhaps it'd be
best to add it unconditionally, or at least to switch the logic and only
skip it on x86_64 and i686.

> Other than that, the main motivation for using gold seems to be the support 
> for
> split-stack, which allows the use of many more goroutines before running out 
> of
> stack space [2]. Replacing GNU ld (`./configure --with-ld=...') as [2] 
> suggests
> may introduce bugs... It appears that in at least one case (ppc64) gccgo
> prefers gold even if gcc was not built solely with it [3]. Unfortunately, 
> adding
> gold as an optional linker would add ~75MiB to closure size...
> 
> I'm not sure what the best way forward is, here. WDYT?

It's not a lot of extra closure size, given just how large the go
package itself is. I think we leave it as-is for now and add change it
up later if necessary.

> 
> [0]: https://github.com/golang/go/issues/15696
> [1]: https://sourceware.org/bugzilla/show_bug.cgi?id=19962
> [2]: https://golang.org/doc/install/gccgo#Gold
> [3]: 
> https://github.com/gcc-mirror/gcc/commit/402565b61f9783473472fcfd729efa8c1e355d2b

-- 
Efraim Flashner   <efraim@flashner.co.il>   אפרים פלשנר
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