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Bug#826987: marked as done (gcc-6: __builtin_cpu_supports() doesn't work on powerpc)

Your message dated Thu, 7 Jul 2016 08:21:15 +0200
with message-id <CA+7wUswxVFwOU3YP1vOnGcRuxdJEFTCpPRdxWcp3pKvg0dcrWg@mail.gmail.com>
and subject line Re: Bug#826987: gcc-6: __builtin_cpu_supports() doesn't work on powerpc
has caused the Debian Bug report #826987,
regarding gcc-6: __builtin_cpu_supports() doesn't work on powerpc
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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-- 
826987: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=826987
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message --- 
Package: gcc-6
Version: 6.1.1-6
Severity: normal

Hi!
According to the documentation: (gcc-6.info.gz)PowerPC Built-in Functions
__builtin_cpu_supports() can be used for detection of a number of CPU
features, such as altivec.  This is same as that function on x86, other
than understandably a different list of features.  The documentation
lists no caveats or other hoops that one needs to jump through to get
the function to work.

Thus, per analogy to x86, I expect the following code to work:
.--====[ altivec.c ]
int main()
{
    __builtin_cpu_init(); // no-op on powerpc anyway
    return !__builtin_cpu_supports("altivec");
}
`----
yet it always returns false.  I've tested both in qemu:
QEMU_CPU=7457_v1.2 ./altivec;echo $?  # should succeed
QEMU_CPU=401 ./altivec2;echo $?       # should fail
and on real hardware (partch.debian.org) whose /proc/cpuinfo says:
cpu		: POWER7 (architected), altivec supported

On the other hand, detection via a "boom instruction" works:
.--====[ altivec2.c ]
int main()
{
    asm("vsldoi %v1,%v1,%v1,0"); // or SIGILL
    return 0;
}
`----

Any other feature supposed to be supported by __builtin_cpu_supports() that
I tested also fails, including "mmu" or "ppc32" which should be true on
every powerpc machine that can run Linux.


-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: powerpc (ppc)

Kernel: Linux 4.6.0+ (SMP w/6 CPU cores)
Locale: LANG=C.UTF-8, LC_CTYPE=C.UTF-8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: sysvinit (via /sbin/init)

Versions of packages gcc-6 depends on:
ii  binutils      2.26-10
ii  cpp-6         6.1.1-6
ii  gcc-6-base    6.1.1-6
ii  libatomic1    6.1.1-6
ii  libc6         2.22-11
ii  libcc1-0      6.1.1-6
ii  libgcc-6-dev  6.1.1-6
ii  libgcc1       1:6.1.1-6
ii  libgmp10      2:6.1.0+dfsg-2
ii  libisl15      0.17.1-1
ii  libmpc3       1.0.3-1
ii  libmpfr4      3.1.4-2
ii  libstdc++6    6.1.1-6
ii  zlib1g        1:1.2.8.dfsg-2+b1

Versions of packages gcc-6 recommends:
ii  libc6-dev  2.22-11

Versions of packages gcc-6 suggests:
pn  gcc-6-doc         <none>
pn  gcc-6-locales     <none>
pn  gcc-6-multilib    <none>
pn  libasan3-dbg      <none>
pn  libatomic1-dbg    <none>
pn  libcilkrts5-dbg   <none>
pn  libgcc1-dbg       <none>
pn  libgomp1-dbg      <none>
pn  libitm1-dbg       <none>
pn  liblsan0-dbg      <none>
pn  libmpx2-dbg       <none>
pn  libquadmath0-dbg  <none>
pn  libtsan0-dbg      <none>
pn  libubsan0-dbg     <none>

-- no debconf information

--- End Message ---
--- Begin Message --- 
reassign 826987 src:glibc 2.22-13
affects src:gcc-6
fixed 826987 2.23-1
thanks

On Wed, Jul 6, 2016 at 8:46 AM, Mathieu Malaterre <malat@debian.org> wrote:
> Control: forwarded -1 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71777
>
> On Tue, Jul 5, 2016 at 10:09 PM, Adam Borowski <kilobyte@angband.pl> wrote:
>> On Tue, Jul 05, 2016 at 08:31:24AM +0200, Mathieu Malaterre wrote:
>>> I cannot see the builtin mentionned anywhere other than on the X86 page:
>>>
>>> X86 (ok):
>>> https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/x86-Built-in-Functions.html#index-g_t_005f_005fbuiltin_005fcpu_005finit-4335
>>>
>>> PowerPC (nothing found):
>>> https://gcc.gnu.org/onlinedocs/gcc-6.1.0/gcc/PowerPC-Built-in-Functions.html#PowerPC-Built-in-Functions
>>
>> It's in the third dash point:
>
> how could I missed that...
>
> [...]
>
>> Should I try asking upstream?
>
> done. I've not tested it on ppc64el.

Indeed:

malat@partch ~ % /lib64/libc-2.23.so
GNU C Library (Debian GLIBC 2.23-1) stable release version 2.23, by
Roland McGrath et al.
Copyright (C) 2016 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.
Compiled by GNU CC version 5.4.0 20160609.
Available extensions:
crypt add-on version 2.1 by Michael Glad and others
GNU Libidn by Simon Josefsson
Native POSIX Threads Library by Ulrich Drepper et al
BIND-8.2.3-T5B
libc ABIs: UNIQUE IFUNC
For bug reporting instructions, please see:
<http://www.debian.org/Bugs/>.

So we need both gcc-6 and glibc ≥ 2.23

--- End Message ---
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