[PATCH] [comiler-rt/ubsan] getVtablePrefix must not sanity-check on Prefix->Offset > 0

[Stephan Bergmann]

ping

On 08/12/2014 09:10 PM, Alexey Samsonov wrote:
> +Richard
>
>
> On Tue, Aug 12, 2014 at 3:51 AM, Stephan Bergmann <sbergman at redhat.com
> <mailto:sbergman at redhat.com>> wrote:
>
>     On 08/11/2014 10:19 PM, Alexey Samsonov wrote:
>
>         +Richard
>
>         Note, that you'd also have to update comment for
>         VtablePrefix::Offset field.
>
>
>     ah, right; updated patch
>
>     Stephan
>
>         On Mon, Aug 11, 2014 at 6:30 AM, Stephan Bergmann
>         <sbergman at redhat.com <mailto:sbergman at redhat.com>
>         <mailto:sbergman at redhat.com <mailto:sbergman at redhat.com>>> wrote:
>
>              At least with recent Clang trunk on Linux x86_64:
>
>                  $ cat test.cc
>                  #include <iostream>
>                  struct A { virtual ~A() {} };
>                  struct B: virtual A {};
>                  struct C: virtual A { ~C() { std::cout << '\n'; } };
>                  struct D: virtual B, virtual C {};
>                  int main() { delete new D; }
>
>                  $ clang++ -fsanitize=undefined test.cc
>
>                  $ ./a.out
>                  <unknown>: runtime error: member call on address
>         0x000002a35010
>                  which does not point to an object of type 'A'
>                  0x000002a35010: note: object has invalid vptr
>                    00 00 00 00  58 0e 43 00 00 00 00 00  30 0e 43 00 00
>         00 00 00
>                    00 00 00 00 00 00 00 00  e1 0f 02 00
>                                 ^~~~~~~~~~~~~~~~~~~~~~~
>                                 invalid vptr
>
>
>              The problem is that getVtablePrefix
>         (lib/ubsan/ubsan_type_hash.cc)
>              rejects any VtablePrefix with Offset > 0 as "This can't
>         possibly be
>              a valid vtable" but, according to the Itanium ABI, "in some
>              construction virtual tables will some virtual base virtual
>         tables
>              have positive offsets."
>
>              The apparent fix is to remove the check, see the attached
>              getVtablePrefix.patch.
>
>
>
>
>
> --
> Alexey Samsonov
> vonosmas at gmail.com <mailto:vonosmas at gmail.com>

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