llvm dev - May 2017 - Dumping the Vtable

Hi,

Can someone help me with how to dump the vtable and the vptr addresses
within it?

Thanks,

Dami
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Hi Damilola,

On Mon, May 29, 2017 at 5:20 AM, Damilola Orikogbo via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Can someone help me with how to dump the vtable and the vptr addresses
> within it?
I'm not sure if this answers your question exactly, but you can pass
"-Xclang -fdump-vtable-layouts" to ask Clang to dump the layout of
generated vtables. For example:

$ cat /tmp/a.cc
struct S {
  virtual void f() {};
};

void f(S * s) {
  s->f();
}
$ bin/clang++ -c /tmp/a.cc -Xclang -fdump-vtable-layouts
Vtable for 'S' (3 entries).
   0 | offset_to_top (0)
   1 | S RTTI
       -- (S, 0) vtable address --
   2 | void S::f()

VTable indices for 'S' (1 entries).
   0 | void S::f()


 - Hans

Hi Hans,

Thanks for the reply. I apologize for the unclear question. I am new to
using clang and llvm.

I have tried this but the version I have for some reason won't allow me to
use this command line option. Furthermore, I am trying to get this
information via the IR  and writing a pass to get this information to use
at a later point.


-Dami

On Tue, May 30, 2017 at 12:56 PM, Hans Wennborg <hans at chromium.org>
wrote:
> Hi Damilola,
>
> On Mon, May 29, 2017 at 5:20 AM, Damilola Orikogbo via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Can someone help me with how to dump the vtable and the vptr addresses
> > within it?
>
> I'm not sure if this answers your question exactly, but you can pass
> "-Xclang -fdump-vtable-layouts" to ask Clang to dump the layout
of
> generated vtables. For example:
>
> $ cat /tmp/a.cc
> struct S {
>   virtual void f() {};
> };
>
> void f(S * s) {
>   s->f();
> }
> $ bin/clang++ -c /tmp/a.cc -Xclang -fdump-vtable-layouts
> Vtable for 'S' (3 entries).
>    0 | offset_to_top (0)
>    1 | S RTTI
>        -- (S, 0) vtable address --
>    2 | void S::f()
>
> VTable indices for 'S' (1 entries).
>    0 | void S::f()
>
>
>  - Hans
>
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