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$!attr.^compose causing segfault #5411

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p6rt opened this issue Jul 2, 2016 · 6 comments
Closed

$!attr.^compose causing segfault #5411

p6rt opened this issue Jul 2, 2016 · 6 comments
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SEGV Segmentation fault, bus error, etc.

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@p6rt
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p6rt commented Jul 2, 2016

Migrated from rt.perl.org#128516 (status was 'resolved')

Searchable as RT128516$
@p6rt
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p6rt commented Jul 2, 2016

From @LLFourn

class Foo { has $.a = Metamodel​::ClassHOW.new_type(name => "Bar"); method
comp { $!a.^compose } };
my $obj = Foo.new;
$obj.comp;
say $obj;

Program received signal SIGSEGV, Segmentation fault.
MVM_6model_istype (tc=0x6037c0, obj=0x207fff00000001, type=0xe19b28,
res=0xea2308) at src/6model/6model.c​:287
287 st = STABLE(obj);
(gdb) bt
#​0 MVM_6model_istype (tc=0x6037c0, obj=0x207fff00000001, type=0xe19b28,
res=0xea2308) at src/6model/6model.c​:287
#​1 0x00007ffff78cecc8 in MVM_interp_run (tc=tc@​entry=0x6037c0,
initial_invoke=0x603010, invoke_data=0xe19b28) at src/core/interp.c​:1777
#​2 0x00007ffff798c589 in MVM_vm_run_file (instance=0x603010,
filename=0x7fffffffe323
"/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/perl6.moarvm")
  at src/moar.c​:304
#​3 0x0000000000401047 in main (argc=8, argv=0x7fffffffdec8) at
src/main.c​:191
(gdb) p STABLE(obj)
Cannot access memory at address 0x207fff00000011

=======
This seems to be caused by doing .^compose on a $! sigiled attribute. If
you do​: $obj.a.^compose it doesn't segfault. Also if you don't *say* the
variable at the end you get a different weird error​:

Unhandled exception​: Cannot assign to a readonly variable or a value
  at gen/moar/m-CORE.setting​:25242
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:ACCEPTS)
from gen/moar/m-CORE.setting​:22293
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:)
from gen/moar/m-CORE.setting​:22268
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:EXCEPTION)
from <unknown>​:1
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:)
from gen/moar/m-CORE.setting​:25242
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:ACCEPTS)
from gen/moar/m-CORE.setting​:25233
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:ACCEPTS)
from gen/moar/m-CORE.setting​:22293
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:)
from gen/moar/m-CORE.setting​:22268
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:EXCEPTION)
from gen/moar/m-CORE.setting​:22332
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:)
from gen/moar/m-CORE.setting​:22331
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:print_exception)
from gen/moar/m-CORE.setting​:22409
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:<anon>)
from gen/moar/m-main.nqp​:44
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/perl6.moarvm​:)
from <unknown>​:1
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/perl6.moarvm​:)
from gen/moar/m-CORE.setting​:19225
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:AT-KEY)
from gen/moar/m-CORE.setting​:6711
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:postcircumfix​:<{
}>)
from gen/moar/m-CORE.setting​:32577
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/CORE.setting.moarvm​:)
from gen/moar/m-main.nqp​:42
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/perl6.moarvm​:MAIN)
from gen/moar/m-main.nqp​:33
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/perl6.moarvm​:<mainline>)
from <unknown>​:1
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/perl6.moarvm​:<main>)
from <unknown>​:1
(/home/llfourn/.rakudobrew/moar-nom/install/share/perl6/runtime/perl6.moarvm​:<entry>)

@p6rt
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p6rt commented Jul 28, 2016

From @nwc10

On Fri, Jul 01, 2016 at 10​:36​:25PM -0700, Lloyd Fournier wrote​:

class Foo { has $.a = Metamodel​::ClassHOW.new_type(name => "Bar"); method
comp { $!a.^compose } };
my $obj = Foo.new;
$obj.comp;
say $obj;

When I run that, I get this​:

moar​: src/gc/roots.c​:245​: MVM_gc_root_gen2_add​: Assertion `!(c->flags & MVM_CF_FORWARDER_VALID)' failed.
Aborted

(I wasn't paying close attention, but I guess I built with full-on debugging
flags)

I hope that makes it more obvious to someone how to fix this.

Nicholas Clark

@p6rt
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p6rt commented Jul 28, 2016

The RT System itself - Status changed from 'new' to 'open'

@p6rt
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p6rt commented Jul 28, 2016

From @LLFourn

Further information​: if you put nqp​::decont($!a).^compose it works.

On Wed, Jul 6, 2016 at 4​:26 AM Nicholas Clark <nick@​ccl4.org> wrote​:

On Fri, Jul 01, 2016 at 10​:36​:25PM -0700, Lloyd Fournier wrote​:

class Foo { has $.a = Metamodel​::ClassHOW.new_type(name => "Bar"); method
comp { $!a.^compose } };
my $obj = Foo.new;
$obj.comp;
say $obj;

When I run that, I get this​:

moar​: src/gc/roots.c​:245​: MVM_gc_root_gen2_add​: Assertion `!(c->flags &
MVM_CF_FORWARDER_VALID)' failed.
Aborted

(I wasn't paying close attention, but I guess I built with full-on
debugging
flags)

I hope that makes it more obvious to someone how to fix this.

Nicholas Clark

@p6rt
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p6rt commented Dec 21, 2016

From @jnthn

On Fri, 01 Jul 2016 22​:36​:25 -0700, lloyd.fourn@​gmail.com wrote​:

class Foo { has $.a = Metamodel​::ClassHOW.new_type(name => "Bar");
method
comp { $!a.^compose } };
my $obj = Foo.new;
$obj.comp;
say $obj;

Program received signal SIGSEGV, Segmentation fault.
MVM_6model_istype (tc=0x6037c0, obj=0x207fff00000001, type=0xe19b28,
res=0xea2308) at src/6model/6model.c​:287
287 st = STABLE(obj);
(gdb) bt
#​0 MVM_6model_istype (tc=0x6037c0, obj=0x207fff00000001,
type=0xe19b28,
res=0xea2308) at src/6model/6model.c​:287
#​1 0x00007ffff78cecc8 in MVM_interp_run (tc=tc@​entry=0x6037c0,
initial_invoke=0x603010, invoke_data=0xe19b28) at
src/core/interp.c​:1777
#​2 0x00007ffff798c589 in MVM_vm_run_file (instance=0x603010,
filename=0x7fffffffe323
"/home/llfourn/.rakudobrew/moar-
nom/install/share/perl6/runtime/perl6.moarvm")
at src/moar.c​:304
#​3 0x0000000000401047 in main (argc=8, argv=0x7fffffffdec8) at
src/main.c​:191
(gdb) p STABLE(obj)
Cannot access memory at address 0x207fff00000011

=======
This seems to be caused by doing .^compose on a $! sigiled attribute.

The SEGV was thanks to MoarVM accidentally allowing recomposition of a P6opaque; I added a check to forbid this and that had the code reliably failing instead of SEGVing. A second fix in the MOP code to always decontainerize the argument to the composetype op was the second part, and this code now works fine. Added a test in S12-meta/classhow.t.

/jnthn

@p6rt p6rt closed this as completed Dec 21, 2016
@p6rt
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p6rt commented Dec 21, 2016

@jnthn - Status changed from 'open' to 'resolved'

@p6rt p6rt added the SEGV Segmentation fault, bus error, etc. label Jan 5, 2020
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