0.5: Illegal instruction 4

[dlfivefifty]

Yet another ApproxFun segfault, that only appears when running all the tests (so hard to isolate).

There's some bizarre behaviour when running the line in question, but does not immediately cause the segfault. I'll try to narrow down the issue.

Julia Version 0.5.0-dev+4850
Commit 9ae4520 (2016-06-18 03:25 UTC)
Platform Info:
  System: Darwin (x86_64-apple-darwin15.5.0)
  CPU: Intel(R) Core(TM) i7-3820QM CPU @ 2.70GHz
  WORD_SIZE: 64
  BLAS: libgfortblas
  LAPACK: liblapack
  LIBM: libopenlibm
  LLVM: libLLVM-3.7.1 (ORCJIT, ivybridge)

Pkg.checkout("ApproxFun","bug-illinstruct")
Pkg.test("ApproxFun")

signal (4): Illegal instruction: 4
while loading /Users/solver/.julia/v0.5/ApproxFun/test/PDETest.jl, in expression starting on line 16
kron at /Users/solver/.julia/v0.5/ApproxFun/src/PDE/KroneckerOperator.jl:295
dirichlet at /Users/solver/.julia/v0.5/ApproxFun/src/PDE/PDE.jl:49
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:86
do_call at /Users/solver/Projects/julia5/src/interpreter.c:65
eval at /Users/solver/Projects/julia5/src/interpreter.c:188
do_call at /Users/solver/Projects/julia5/src/interpreter.c:64
eval at /Users/solver/Projects/julia5/src/interpreter.c:188
eval_body at /Users/solver/Projects/julia5/src/interpreter.c:469
jl_interpret_call at /Users/solver/Projects/julia5/src/interpreter.c:573
jl_toplevel_eval_flex at /Users/solver/Projects/julia5/src/toplevel.c:543
jl_parse_eval_all at /Users/solver/Projects/julia5/src/ast.c:699
jl_load at /Users/solver/Projects/julia5/src/toplevel.c:569
include_from_node1 at ./loading.jl:426
unknown function (ip: 0x1115b453c)
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:86
do_call at /Users/solver/Projects/julia5/src/interpreter.c:65
eval at /Users/solver/Projects/julia5/src/interpreter.c:188
jl_toplevel_eval_flex at /Users/solver/Projects/julia5/src/toplevel.c:529
jl_parse_eval_all at /Users/solver/Projects/julia5/src/ast.c:699
jl_load at /Users/solver/Projects/julia5/src/toplevel.c:569
include_from_node1 at ./loading.jl:426
unknown function (ip: 0x1115b453c)
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:86
process_options at ./client.jl:266
_start at ./client.jl:322
unknown function (ip: 0x1115dfbc4)
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:86
true_main at /Users/solver/Projects/julia5/usr/bin/julia (unknown line)
main at /Users/solver/Projects/julia5/usr/bin/julia (unknown line)
Allocations: 429519734 (Pool: 429304528; Big: 215206); GC: 866
====================================================[ ERROR: ApproxFun ]====================================================

failed process: Process(`/Users/solver/Projects/julia5/usr/bin/julia -Cnative -J/Users/solver/Projects/julia5/usr/lib/julia/sys.dylib --compile=yes --depwarn=yes --check-bounds=yes --code-coverage=none --color=yes /Users/solver/.julia/v0.5/ApproxFun/test/runtests.jl`, ProcessSignaled(4)) [0]

============================================================================================================================
ERROR: ApproxFun had test errors
 in #test#49(::Bool, ::Function, ::Array{AbstractString,1}) at ./pkg/entry.jl:694
 in (::Base.Pkg.Entry.#kw##test)(::Array{Any,1}, ::Base.Pkg.Entry.#test, ::Array{AbstractString,1}) at ./null:0
 in (::Base.Pkg.Dir.##2#3{Array{Any,1},Base.Pkg.Entry.#test,Tuple{Array{AbstractString,1}}})() at ./pkg/dir.jl:31
 in cd(::Base.Pkg.Dir.##2#3{Array{Any,1},Base.Pkg.Entry.#test,Tuple{Array{AbstractString,1}}}, ::String) at ./file.jl:59
 in #cd#1(::Array{Any,1}, ::Function, ::Function, ::Array{AbstractString,1}, ::Vararg{Array{AbstractString,1},N}) at ./pkg/dir.jl:31
 in (::Base.Pkg.Dir.#kw##cd)(::Array{Any,1}, ::Base.Pkg.Dir.#cd, ::Function, ::Array{AbstractString,1}, ::Vararg{Array{AbstractString,1},N}) at ./null:0
 in #test#3(::Bool, ::Function, ::String, ::Vararg{String,N}) at ./pkg/pkg.jl:245
 in test(::String, ::Vararg{String,N}) at ./pkg/pkg.jl:245
 in eval(::Module, ::Any) at ./boot.jl:231
 in macro expansion at ./REPL.jl:92 [inlined]
 in (::Base.REPL.##1#2{Base.REPL.REPLBackend})() at ./event.jl:46

[dlfivefifty]

Here's a non-crashing version of the inconsistency:

dirichlet(Interval()^2)

displays no output while

@code_typed dirichlet(Interval()^2)

shows that the return type is

Array{ApproxFun.Operator{BandedMatrices.BandedMatrix{Float64}},1})

[dlfivefifty]

Nevermind, that is due to a questionable override of Base.writemime

[yuyichao]

SIGILL is likely due to functions that returns unexpectedly. You could check @code_llvm (look for @llvm.trap) to figure out which function it was

[dlfivefifty]

I managed to trigger it with a shorter sequence in julia-debug by running the following in a .jl file (running on command prompt or deleting lines does not trigger the crash!):

using ApproxFun

dx=dy=Interval()
d=dx*dy
x=Fun(identity,dx);y=Fun(identity,dy)

G=[real(exp(-1+1.0im*y));
                        real(exp(1+1im*y));
                        real(exp(x-1im));
                        real(exp(x+1im));0.];

A=[dirichlet(d);lap(d)]

Here's the versioninfo:

Julia Version 0.5.0-dev+4850
Commit 9ae4520 (2016-06-18 03:25 UTC)
DEBUG build
Platform Info:
  System: Darwin (x86_64-apple-darwin15.5.0)
  CPU: Intel(R) Core(TM) i7-3820QM CPU @ 2.70GHz
  WORD_SIZE: 64
  BLAS: libgfortblas
  LAPACK: liblapack
  LIBM: libopenlibm
  LLVM: libLLVM-3.7.1 (ORCJIT, ivybridge)

[dlfivefifty]

This is still present in the latest build. I tried working around it by changing the offending line from a comprehension to an explicit constructed array, but the bug remained.

[dlfivefifty]

The latest build gives a bit more information: apparently a call to copy! is the trigger:

while loading /Users/solver/.julia/v0.5/ApproxFun/test/PDETest.jl, in expression starting on line 16
copy! at ./abstractarray.jl:393
kron at /Users/solver/.julia/v0.5/ApproxFun/src/PDE/KroneckerOperator.jl:298
dirichlet at /Users/solver/.julia/v0.5/ApproxFun/src/PDE/PDE.jl:49
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:177 [inlined]
jl_apply_generic at /Users/solver/Projects/julia5/src/gf.c:2034
do_call at /Users/solver/Projects/julia5/src/interpreter.c:66
eval at /Users/solver/Projects/julia5/src/interpreter.c:190
do_call at /Users/solver/Projects/julia5/src/interpreter.c:65
eval at /Users/solver/Projects/julia5/src/interpreter.c:190
eval_body at /Users/solver/Projects/julia5/src/interpreter.c:469
jl_interpret_call at /Users/solver/Projects/julia5/src/interpreter.c:573
jl_toplevel_eval_flex at /Users/solver/Projects/julia5/src/toplevel.c:572
jl_parse_eval_all at /Users/solver/Projects/julia5/src/ast.c:717
jl_load at /Users/solver/Projects/julia5/src/toplevel.c:596 [inlined]
jl_load_ at /Users/solver/Projects/julia5/src/toplevel.c:605
include_from_node1 at ./loading.jl:426
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:177 [inlined]
jl_apply_generic at /Users/solver/Projects/julia5/src/gf.c:2034
do_call at /Users/solver/Projects/julia5/src/interpreter.c:66
eval at /Users/solver/Projects/julia5/src/interpreter.c:190
jl_toplevel_eval_flex at /Users/solver/Projects/julia5/src/toplevel.c:558
jl_parse_eval_all at /Users/solver/Projects/julia5/src/ast.c:717
jl_load at /Users/solver/Projects/julia5/src/toplevel.c:596 [inlined]
jl_load_ at /Users/solver/Projects/julia5/src/toplevel.c:605
include_from_node1 at ./loading.jl:426
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:177 [inlined]
jl_apply_generic at /Users/solver/Projects/julia5/src/gf.c:2034
process_options at ./client.jl:262
_start at ./client.jl:318
jl_call_method_internal at /Users/solver/Projects/julia5/src/./julia_internal.h:177 [inlined]
jl_apply_generic at /Users/solver/Projects/julia5/src/gf.c:2034
true_main at /Users/solver/Projects/julia5/usr/bin/julia (unknown line)
main at /Users/solver/Projects/julia5/usr/bin/julia (unknown line)
Allocations: 480657994 (Pool: 480586587; Big: 71407); GC: 913

[ViralBShah]

Would this be a regression that we need to fix for 0.5?

[dlfivefifty]

Yes, it’s fine in 0.4 and it was actually working fine in 0.5 a month ago or so.

On 23 Jul 2016, at 9:13 AM, Viral B. Shah notifications@github.com wrote:

Would this be a regression that we need to fix for 0.5?

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You are receiving this because you authored the thread.
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[yuyichao]

See also my very early comment above #17003 (comment) if you are still seeing a sigill.

[dlfivefifty]

I haven't been able to find @llvm.trap

[yuyichao]

So what's the instruction it fails on in the debugger?

[dlfivefifty]

I don't know how to use the debugger.

[dlfivefifty]

OK I brew installed gdb, and tried running the script but get the error

Unable to find Mach task port for process-id 54432: (os/kern) failure (0x5).
 (please check gdb is codesigned - see taskgated(8))

[dlfivefifty]

OK I got it working, here is what bt returns:

Thread 1 received signal SIGILL, Illegal instruction.
0x000000030d276ab3 in ?? ()
(gdb) bt
#0  0x000000030d276ab3 in ?? ()
#1  0x00007fff5fbfd940 in ?? ()
#2  0xbff0000000000000 in ?? ()
#3  0x3ff0000000000000 in ?? ()
#4  0x0000000114752300 in ?? ()
#5  0x0000000000000000 in ?? ()