[erlang-bugs] FreeBSD FPE issue on ERTS_FP_CHECK_INIT Re: ERTS_FP_CHECK_INIT error of HiPE in 18.0-rc1 running on FreeBSD 10.1-STABLE

[Mikael Pettersson]

Mikael Pettersson writes:
 > Kenji Rikitake writes:
 >  > Thanks Mikael for the confirmation.
 >  > 
 >  > So can I conclude this as a bug or FPE handling
 >  > difference between gcc and clang?
 > 
 > Yes.  I have a reduced testcase in plain C99 which works with gcc
 > but shows wrong behaviour when compiled by clang.  It involves
 > converting a double with value somewhere between INT64_MAX and
 > UINT64_MAX to uint64_t: clang causes that to signal FP_INVALID.
 > 
 > At the moment I'm trying to get confirmation about where the
 > error lies: in the test case (i.e., the Erlang VM), or in clang.
 > According to my reading of the C standard, clang is in error.

I've had a look in clang/llvm's bugzilla, and it's clear that clang/llvm
does not support FP exceptions in any way -- both due to backend bugs
and due to their middle-end being reckless.  See e.g. PRs 17686, 22873,
and 8100.

I'll prepare a patch to force-disable FP exceptions if clang is detected.

/Mikael

 > 
 > For now, the workaround is to either compile with gcc, or to
 > build with ./configure --disable-fp-exceptions.
 > 
 > /Mikael
 > 
 >  > (I noticed on my OS X the *gcc-compiled* 18.0-rc1
 >  > didn't cause the problem either.)
 >  > 
 >  > Regards,
 >  > Kenji Rikitake
 >  > 
 >  > On Sat, May 2, 2015 at 3:04 AM, Mikael Pettersson <mikpelinux@REDACTED>
 >  > wrote:
 >  > 
 >  > > Kenji Rikitake writes:
 >  > >  > Mikael:
 >  > >  >
 >  > >  > I managed to reduce the problem to a one-liner.
 >  > >  > Executing
 >  > >  > trunc(0.8 * (1 bsl 128))
 >  > >  > will generate the SIGFPE.
 >  > >
 >  > > I can reproduce the SIGFPE on Linux/x86_64 by compiling OTP-18-rc1 with
 >  > > clang-3.6.0.
 >  > >
 >  > >
 >  > >  >
 >  > >  > I attached the gdb of FreeBSD 10.1-STABLE to the Erlang beam.smp and
 >  > > generated
 >  > >  > the following output.
 >  > >  > Regards,
 >  > >  > Kenji Rikitake
 >  > >  >
 >  > >  > --- Erlang shell output:
 >  > >  >
 >  > >  > Erlang/OTP 18 [RELEASE CANDIDATE 1] [erts-7.0] [source-71bfef4]
 >  > > [64-bit] [smp:4:4] [async-threads:10] [kernel-poll:false] [dtrace]
 >  > >  >
 >  > >  > Eshell V7.0  (abort with ^G)
 >  > >  > 1> trunc(0.8 * (1 bsl 128)).
 >  > >  > %%% here FPE is issued and the gdb shows the value...
 >  > >  > fpe_sig_action: FPE at 0x4ca1b7
 >  > >  > 272225893536750785882272431128279252992
 >  > >  > 2> trunc(0.8 * (1 bsl 128)).
 >  > >  > ERTS_FP_CHECK_INIT at 0x571e60: detected unhandled FPE at
 >  > > 0x4cafpe_sig_action: FPE at 0x4ca1b7
 >  > >  > 272225893536750785882272431128279252992
 >  > >  > 3> q()
 >  > >  > ok
 >  > >  >
 >  > >  > --- output of attached gdb:
 >  > >  >
 >  > >  > Continuing.
 >  > >  >
 >  > >  > Program received signal SIGFPE, Arithmetic exception.
 >  > >  > [Switching to Thread 80240a000 (LWP 101243/beam.smp)]
 >  > >  > double_to_integer (p=0x8031c0398, x=1.4757395258967642e+19) at
 >  > > beam/erl_bif_guard.c:302
 >  > >  > 302             d = x;            /* trunc */
 >  > >  > Current language:  auto; currently minimal
 >  > >  > (gdb) print $mxcsr
 >  > >  > $1 = 6401
 >  > >  > (gdb) disassemble double_to_integer
 >  > >  > Dump of assembler code for function double_to_integer:
 >  > >  > [...]
 >  > >  > 0x00000000004ca1b7 <double_to_integer+519>:     cvttsd2siq %xmm1,%rcx
 >  > >  > [...]
 >  > >  > End of assembler dump.
 >  > >  > (gdb) print $mxcsr
 >  > >  > $3 = 6401
 >  > >  > (gdb) print $xmm1
 >  > >  > $4 = {f = {-1.58818684e-23, 467.199982, 0, 0}}
 >  > >  > (gdb) print $rcx
 >  > >  > $5 = -9223372036854775808
 >  > >  >
 >  > >  > [End of log]
 >  > >  >
 >  > >  > ++> Kenji Rikitake <kenji@REDACTED> [2015-04-27 21:53:44 +0900]:
 >  > >  > > Date: Mon, 27 Apr 2015 21:53:44 +0900
 >  > >  > > From: Kenji Rikitake <kenji@REDACTED>
 >  > >  > > To: Mikael Pettersson <mikpelinux@REDACTED>
 >  > >  > > Cc: erlang-bugs@REDACTED
 >  > >  > > Subject: Re: [erlang-bugs] FreeBSD FPE issue on ERTS_FP_CHECK_INIT Re:
 >  > >  > >  ERTS_FP_CHECK_INIT error of HiPE in 18.0-rc1 running on FreeBSD
 >  > >  > >  10.1-STABLE
 >  > >  > >
 >  > >  > > FYI:
 >  > >  > > A reference on a similar issue on OS X:
 >  > >  > > http://erlang.org/pipermail/erlang-bugs/2011-May/002383.html
 >  > >  > >
 >  > >  > > The instruction caused the exception was "cvttsd2siq".
 >  > >  > >
 >  > >  > > Kenji Rikitake
 >  > >  > >
 >  > >  > > ++> Kenji Rikitake <kenji@REDACTED> [2015-04-27 21:16:14 +0900]:
 >  > >  > > > > Can you provide a disassembly of erts_gc_trunc_1 from this build?
 >  > >  > > >
 >  > >  > > > > Can you provide a disassembly of gc_double_to_integer from this
 >  > > build?
 >  > >  > > >
 >  > >  > > > I will send you personally (not on the list).
 >  > >  > > _______________________________________________
 >  > >  > > erlang-bugs mailing list
 >  > >  > > erlang-bugs@REDACTED
 >  > >  > > http://erlang.org/mailman/listinfo/erlang-bugs
 >  > >
 >  > > --
 >  > >
 > 
 > -- 

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