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| author | Ahmed Bougacha <ahmed@bougacha.org> | 2024-06-14 17:57:12 -0700 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2024-06-14 17:57:12 -0700 |
| commit | 61069bd5a3954076018ed30c77094d6259bcbc90 (patch) | |
| tree | 22e3b9607aae02c4727fa07b2850d43392027eda /llvm/lib/ProfileData/Coverage/CoverageMapping.cpp | |
| parent | a0cef2bf71c5fb7a643656371d8e6cc58271fbe6 (diff) | |
| download | llvm-61069bd5a3954076018ed30c77094d6259bcbc90.zip llvm-61069bd5a3954076018ed30c77094d6259bcbc90.tar.gz llvm-61069bd5a3954076018ed30c77094d6259bcbc90.tar.bz2 | |
[Support] Add SipHash-based 16-bit ptrauth ABI-stable hash. (#93902)
This finally wraps the now-lightly-modified SipHash C reference
implementation, for the main interface we need (16-bit ptrauth
discriminators).
The exact algorithm is the little-endian interpretation of the
non-doubled (i.e. 64-bit) result of applying a SipHash-2-4 using the
constant seed `b5d4c9eb79104a796fec8b1b428781d4` (big-endian), with the
result reduced by modulo to the range of non-zero discriminators (i.e.
`(rawHash % 65535) + 1`).
By "stable" we mean that the result of this hash algorithm will the same
across different compiler versions and target platforms.
The 16-bit hashes are used extensively for the AArch64 ptrauth ABI,
because AArch64 can efficiently load a 16-bit immediate into the high
bits of a register without disturbing the remainder of the value, which
serves as a nice blend operation.
16 bits is also sufficiently compact to not inflate a loader relocation.
We disallow zero to guarantee a different discriminator from the places
in the ABI that use a constant zero.
Co-authored-by: John McCall <rjmccall@apple.com>
Diffstat (limited to 'llvm/lib/ProfileData/Coverage/CoverageMapping.cpp')
0 files changed, 0 insertions, 0 deletions