[cfe-dev] [llvm-dev] AST of whole program

[Anil Altinay via cfe-dev]

Hi Vedant,


*What kind of transformation are you interested in, and what kind of
programsare you looking to transform?*

I am trying to change the layout of fields(randomize) in a struct in a
c program. I already figured out how to change the layout of fields in a
struct but there are structs that I should not touch like structs defined
in libraries. So if I randomize a struct in one compilation unit and then
realize that actually, I shouldn't have randomized it when clang was
working on another compilation unit, there is no way to go back and revert
the layout of the struct that I already randomized in previous translation
unit because it is already over. So what I am thinking is I should look all
the translation units in AST level before they create llvm IR and decide
which structs I should randomize, then randomize the structs I have decided
to randomize, then let clang to create llvm IR using modified ASTs.

I am trying to transform programs like apache.


*By 'AST of whole program', do you mean AST's for the source from all
librarieslinked into the program?*

I am not sure if I understand your question but I will try to explain what
I meant. For each translation unit, AST gets created. The problem is I can
only see AST of current translation unit. I cannot see AST of next
translation unit because clang works on one translation unit at a time.
Maybe I should dump AST of each translation unit to the disk, decide which
structs can be randomized, change the AST on the disk and start compilation
from modified ASTs. But this may be so slow and I do not really know how I
can do this.

Also I am not sure about one thing. Can I make sure that a struct is
defined in a library or in the source code of the program by looking only
one translation unit without any false flag? If I can, then there is no
need for what I am asking for.

I hope that I explained what I am trying to do clearly. If you have any
suggestion how I should do this, I would really appreciate hearing your
opinion. Thank you very much for your quick response.

Anil




On Tue, Oct 4, 2016 at 5:58 PM, Vedant Kumar <vsk at apple.com> wrote:

> - llvm-dev, + cfe-dev
>
> Hi,
>
> What kind of transformation are you interested in, and what kind of
> programs
> are you looking to transform?
>
> By 'AST of whole program', do you mean AST's for the source from all
> libraries
> linked into the program?
>
> vedant
>
>
> > On Oct 4, 2016, at 5:50 PM, Anil Altinay via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Hello,
> >
> > I would like to do transformations on AST of a c program but I need to
> have access to all ASTs created for the program to do right changes. LLVM
> processes one translation unit at a time and because of it, I do not have
> access to AST of all the translation units at the same time. Do you have
> any suggestion how I can access all the ASTs created for a program, do
> analysis on the ASTs and do modifications on the ASTs?
> >
> > As a summary:
> >
> >       • I need to have access to ASTs of the program at the same time.
> >       • Do analysis on ASTs.
> >       • Modify ASTs based on my analysis and create llvm IR from
> modified ASTs.
> > Thank you,
> > Anil
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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