[PATCH] D148665: Change -fsanitize=function to place two words before the function entry

Tue May 9 13:12:25 PDT 2023

MaskRay added a comment.

In D148665#4316310 <https://reviews.llvm.org/D148665#4316310>, @peter.smith wrote:

> My apologies for not responding. If I've got this right there are 4 related patches:
> D148573 <https://reviews.llvm.org/D148573> (approved)
> D148785 <https://reviews.llvm.org/D148785> Use type hashes rather than RTTI 
> D148827 <https://reviews.llvm.org/D148827> support C
> D148665 <https://reviews.llvm.org/D148665> (this one)

> My initial impressions is that this makes -fsanitize=function look more like -fsanitize=kcfi which makes it accessible from C and available to more targets. Is there anything that we lose in the process of making these changes? For example I would expect RTTI to have more information available than a type hash, although this might not make any functional difference.
>
> I'll try and look over the next few days and leave some comments, apologies a bit busy at work at the moment so I can't promise anything speedy.

Thanks! `-fsanitize=function` will indeed become more like `-fsanitize=kcfi`.

There is a big difference that `-fsanitize=function` instrumented code has a signature check for compatibility with object files not compiled with `-fsanitize=function` (and old implementations of `-fsanitize=function` with a difference location to place the signature).
-fsanitize=kcfi doesn't have the compatibility guarantee.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D148665/new/

https://reviews.llvm.org/D148665