[llvm-dev] RFC: Loadable segments watermark for lld

Chris Jackson via llvm-dev llvm-dev at lists.llvm.org
Thu Nov 21 03:43:16 PST 2019

Hello all,

I'm implementing a watermarking feature for lld that computes a hash of
segments and places the result in a note section. Ongoing work can be found


The purpose of this watermark is to enable detection of post-link
to the loadable segments of the binary. Such modifications may produce a
that relies on functionality that is an incidental detail of the OS that may
change in a future update and negatively affect the runtime behaviour of the

As well as identifying reliance on unspecified behaviour, on detection of
post-link changes we can then look at improving our tooling to support
changes had been applied.

Its critical for us that the watermark has minimal impact on build time and
cryptographic security is not the goal. Hence, xxhash is used as our
experiments showed it has minimal overhead.

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