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[scudo] 32-bit and hardware agnostic support

Description

[scudo] 32-bit and hardware agnostic support

Summary:
This update introduces i386 support for the Scudo Hardened Allocator, and
offers software alternatives for functions that used to require hardware
specific instruction sets. This should make porting to new architectures
easier.

Among the changes:

  • The chunk header has been changed to accomodate the size limitations encountered on 32-bit architectures. We now fit everything in 64-bit. This was achieved by storing the amount of unused bytes in an allocation rather than the size itself, as one can be deduced from the other with the help of the GetActuallyAllocatedSize function. As it turns out, this header can be used for both 64 and 32 bit, and as such we dropped the requirement for the 128-bit compare and exchange instruction support (cmpxchg16b).
  • Add 32-bit support for the checksum and the PRNG functions: if the SSE 4.2 instruction set is supported, use the 32-bit CRC32 instruction, and in the XorShift128, use a 32-bit based state instead of 64-bit.
  • Add software support for CRC32: if SSE 4.2 is not supported, fallback on a software implementation.
  • Modify tests that were not 32-bit compliant, and expand them to cover more allocation and alignment sizes. The random shuffle test has been deactivated for linux-i386 & linux-i686 as the 32-bit sanitizer allocator doesn't currently randomize chunks.

Reviewers: alekseyshl, kcc

Subscribers: filcab, llvm-commits, tberghammer, danalbert, srhines, mgorny, modocache

Differential Revision: https://reviews.llvm.org/D26358

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