[PATCH] D53906: [ELF] Allow configuring the TLS layout for an Android executable

[Ryan Prichard via Phabricator via llvm-commits]

rprichard added a comment.

In https://reviews.llvm.org/D53906#1284881, @ruiu wrote:

> What I'm currently seeking is a simple way to create executables/DSOs that are compatible on non-Android and Android, without introducing any new command line flag or a target-dependent logic. I believe it is OK to waste a few words on non-Android if we can achieve that goal. Another idea that is in line with that is to always set a >8 word alignment (you suggested 16, but I don't know why it has to be 16) to a TLS segment if ARM or AArch64. Maybe that could produce a binary that is compatible both Android and non-Android?


We'd only need 9 words to reserve all the existing Bionic TLS slots. (TSAN is slot 8.) 16 provides a few spare slots for the future, assuming Bionic wants to keep using positive slot indices (but it really could just negative indices). If we use alignment for reservation, that'd also require a power-of-two.

If we can move the TSAN slot, then an alignment of >8 would work for both Android and non-Android.

It looks like the ASAN runtime libraries shipped with NDK r18 don't use the TSAN slot, and the NDK doesn't support -fsanitize=thread (yet), so maybe moving the slot is feasible?


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D53906