[perl #70530] Calling multimethod causes segfault

[Arne Skjærholt]

# New Ticket Created by Arne Skjærholt
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This code snippet: class T does Associative { multi method
postcircumfix:<{ }> { }; }; my T $t .= new; say $t<a>; causes a
segfault on Rakudo on OS X 10.6.2.

Recompiling Rakudo with -O0 -g gives some interesting data in gdb:
278 GETATTR_P6LowLevelSig_elements(interp, signature,
sig_elem_info);

(gdb) p *signature
$8 = {
flags = 266752,
vtable = 0x10183d000,
data = 0x0,
_metadata = 0x0,
_synchronize = 0x0
}

The culprit is on line 47 of src/pmc/p6_lowlevelsig.h, which calls
PMC_data(signature)->elements. Since signature->data is NULL, we get a
NULL pointer dereference.