[PATCH] D129107: [BOLT][HUGIFY] adds huge pages support of PIE/no-PIE binaries

[Rafael Auler via Phabricator via llvm-commits]

rafauler added a comment.

Ok, because of the weird ASLR thing on older kernels, now it is clear that the extra padding is going to be necessary for every PIE binary. So instead of having --hugify-extra-padding, we can kill this flag and always insert the extra padding whenever a PIE binary is being processed with -hugify.

To detect whether the input is PIE or not, use !HasFixedLoadAddress:
https://github.com/llvm/llvm-project/blob/main/bolt/include/bolt/Core/BinaryContext.h#L606

So just replace opts::HugifyExtraPadding with !BC.hasFixedLoadAddress.

So now it's clear the case for hugifyForOldKernel(HotStart, HotEnd, AlignedFrom, AlignedTo) with 4 args.  But.. it still should copy the entire page  contents instead of just hot code.  When you ask the kernel to unmap all these addresses, we need first to copy whatever was there before, even if it was all zeroes (because in the no-PIC case, it won't be just zeroes).


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D129107/new/

https://reviews.llvm.org/D129107