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
