Bug#767138: libfftw3 SIGILL on armhf

[Kamal Mostafa]

I'm investigating an armhf FTBFS of my package 'minimodem'[0], which I now
suspect might be caused by this libfftw3 bug in unstable:

#767138 "fftw3: runtime detection of NEON is perhaps broken"
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=767138

There, Edmund points out that "#752514 ruby-fftw3: FTBFS on armhf" [1] is
possibly caused by that fftw3 bug.  But Cédric notes that he was unable to
reproduce the ruby failure on harris.debian.org.  I am seeing exactly the
same issues with minimodem:  On the armhf buildd builders (only), minimodem
compiles fine but then all its test cases fail.  But when I try it on
harris.d.o (or asachi.d.o), I cannot reproduce any problem.

But I've just discovered that I *can* reproduce the minimodem crash on
abel.debian.org, and it points to libfftw3:

Linux abel 3.16-0.bpo.2-armmp-lpae #1 SMP Debian 3.16.3-2~bpo70+1
(2014-09-21) armv7l GNU/Linux
(sid_armhf-dchroot)

Program received signal SIGILL, Illegal instruction.

0xb6f47e9a in ?? () from /usr/lib/arm-linux-gnueabihf/libfftw3f.so.3


For comparison, harris and asachi (where no problem occurs) are:

Linux harris 3.2.0-4-mx5 #1 Debian 3.2.63-2+deb7u1 armv7l GNU/Linux
(sid_armhf-dchroot)

Linux asachi 3.16-2-arm64 #1 SMP Debian 3.16.3-2 (2014-09-20) armv8l
GNU/Linux
(sid_armhf-dchroot)



Edmund et al., I would appreciate your expertise here... Does it also
appear to you that my minimodem (0.20-1) failure[0] could be caused by the
fftw3 "NEON is perhaps broken" bug?   Does it make sense that abel.d.o
would be affected by it, but harris and asachi would not?

Cédric, you might want to re-try your ruby-fftw3 build test on
abel.debian.org and consider re-opening #752514 [1].

Hector, could this situation result in a possible inconsistency among the
armhf buildd's? (Or at least, among the porterbox armhf chroots)?

All: Should the severity of the libfftw3 bug #767138 be elevated to
"serious"?

Thanks in advance for your help,

 -Kamal


[0] #769974 "minimodem: FTBFS on armhf"
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=769974


     To replicate the minimodem failure for debugging:

(sid_armhf-dchroot)$ echo hello | src/minimodem --tx -f /tmp/foo.wav 1200
 # this does not call libfftw3

(sid_armhf-dchroot)$ gdb  --args  src/minimodem --rx -f /tmp/foo.wav 1200
...
Program received signal SIGILL, Illegal instruction.
0xb6f47e9a in ?? () from /usr/lib/arm-linux-gnueabihf/libfftw3f.so.3


[1] #752514 "ruby-fftw3: FTBFS on armhf"
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=752514
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