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Re: [buildd] unexpected FTBFS on amd64 buildd «binet»

On Sun, Oct 16, 2016 at 02:14:47PM +0000, lumin wrote:
> My package lua-torch-torch7/experimental fails[2] to build from
> source because of an "illegal instruction" error at the debhelper
> auto test stage. However from that buildlog I can't tell which
> program to blame -- luajit or lua-torch-torch7.
> The upstream code indeed contains instruction specific stuff but
> I have never encountered such failure on amd64 architecture.
> Besides, I tested this package with debomatic-amd64[3] and the
> result is quite healthy.
> So I have trouble allocating where the source of problem is.
> Cosmic ray?
> My questions:
>  * should we suspect the health state of that amd64 buildd
>    machine «binet»?

I'd bet first on a real SIGILL.

This can come from two sources:
* using an instruction specific to a particular CPU, such as, say,
  ADDSUBPD on x86 with no SSE3, DMB on RasPi 1, MTVSRD on ppc64el
  when ran on qemu from jessie, etc
* executing some junk memory

Failing on the buildd but not on your home box suggests the former.

If you don't have access to a diverse set of CPUs to test, I'd recommend
using qemu _without_ kvm.  You can choose a specific CPU to emulate via
either QEMU_CPU=z80 or -cpu z80; "qemu-system-x86_64 -cpu help" to get the
list of valid targets.  Perversely, it's easier to test this from a non-x86
host as qemu-user+binfmt make running foreign binaries convenient -- if all
what you have is a x86 box, I'd recommend qemu-system-x86_64 as using
qemu-user for same ISA, while possible, is too tricky to get it right.

qemu-system means you need to set up a whole virtual machine.

>  * what should I do next? do a binary-only amd64 upload or
>    request (and how) for a rebuild against that package?

Please don't.  It fails in the test suite, which means it'd break the same
way on user systems that don't support that particular extension.

> I encountered an unexpected FTBFS on amd64 that I can't repro.[1]
> And I'd like to ask the list before fixing it by e.g. an binary
> only upload.

As the page at [1] is almost entirely red, I'd say you have a good deal more
to investigate befor applying workarounds.


> [1] https://buildd.debian.org/status/package.php?p=lua-torch-torch7&suite=experimental
> [2] https://buildd.debian.org/status/fetch.php?pkg=lua-torch-torch7&arch=amd64&ver=0%7E20161013-g4f7843e-1&stamp=1476616893
> [3] http://debomatic-amd64.debian.net/distribution#experimental/lua-torch-torch7/0~20161013-g4f7843e-1/buildlog

A MAP07 (Dead Simple) raspberry tincture recipe: 0.5l 95% alcohol, 1kg
raspberries, 0.4kg sugar; put into a big jar for 1 month.  Filter out and
throw away the fruits (can dump them into a cake, etc), let the drink age
at least 3-6 months.

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