[cfe-dev] Implementing linux randstruct plugin for clang?

[Hal Finkel via cfe-dev]

On 09/22/2017 02:05 PM, Friedman, Eli via cfe-dev wrote:
> On 9/22/2017 8:49 AM, Vlad Tsyrklevich wrote:
>> I thought a little about implementing PAX_RANDSTRUCT for clang a 
>> couple months back but I didn't get to the point where I implemented 
>> anything. My notes indicate that my two ideas at the time I left it 
>> were: (1) see if there's a point between parsing and codegen that a 
>> clang plugin could insert a TreeTransform to rewrite struct 
>> definitions, or (2) perform randomization as an LLVM pass that 
>> rewrites types and the GEPs, GVs, etc. referencing those types.
>>
>> For approach #2 you would need to hook into offsetof()--Linux defines 
>> offsetof() as both __builtin_offsetof() and ((size_t) &((TYPE 
>> *)0)->MEMBER) in different places. The latter would transform into a 
>> GEP and shouldn't require special casing, while the former might mean 
>> it's not doable as an LLVM pass alone. Thinking about it now, if you 
>> wanted to implement the unoptimized version of RANDSTRUCT (where 
>> elements are randomized across cache lines) you would also need to 
>> hook into sizeof() as well. I might be missing other code constructs 
>> that would further complicate the pass approach.
>
> The very latest point you can reorder the members of a struct without 
> imposing weird restrictions is in RecordLayoutBuilder (which is run as 
> part of semantic analysis). After that, constant-folding of 
> sizeof/offsetof/etc. starts happening.

How does this work across translation units?

  -Hal

>
> -Eli
>

-- 
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory