[PATCH] D61824: [ARM][AArch64] Overalign .tbss (Android Bionic hack) to avoid p_vaddr%p_align!=0

[Rich Felker via Phabricator via llvm-commits]

dalias added a comment.

The waste is not just 48 bytes in the ELF image on disk, but up to 63 bytes in each thread. Depending on how that falls, the waste is likely actually either 0 bytes or 4096 bytes per thread, since the memory is allocated with page granularity.

Forcing the alignment will also force musl to *always* mmap space (on page granularity, so A LOT of waste) for the main thread's TLS at startup, rather than using the built-in bss space intended to be used when the application's TLS needs are small, since the built-in space does not have excess alignment. This imposes a syscall as well, and a new failure mode for static-linked binaries that may have been intended not to be able to fail after exec.

Please, drop this ridiculous and costly hack for Bionic or put it under the --android-tls option or whatever.


Repository:
  rLLD LLVM Linker

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  https://reviews.llvm.org/D61824/new/

https://reviews.llvm.org/D61824