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Auto merge of #38357 - arielb1:deterministic-hash, r=michaelwoerister
make deterministic_hash host-architecture-independent `DefPath::deterministic_hash` used to call `std::hash::Hash`, which depends on the current architecture in several ways, which would prevent metadata written on one host architecture from being successfully read on another one. Use a hasher we control instead. Fixes #38177. r? @michaelwoerister
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,176 @@ | ||
| // Copyright 2016 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
|
|
||
| use std::hash::Hasher; | ||
| use std::marker::PhantomData; | ||
| use std::mem; | ||
| use blake2b::Blake2bHasher; | ||
| use rustc_serialize::leb128; | ||
|
|
||
| fn write_unsigned_leb128_to_buf(buf: &mut [u8; 16], value: u64) -> usize { | ||
| leb128::write_unsigned_leb128_to(value, |i, v| buf[i] = v) | ||
| } | ||
|
|
||
| fn write_signed_leb128_to_buf(buf: &mut [u8; 16], value: i64) -> usize { | ||
| leb128::write_signed_leb128_to(value, |i, v| buf[i] = v) | ||
| } | ||
|
|
||
| /// When hashing something that ends up affecting properties like symbol names. We | ||
| /// want these symbol names to be calculated independent of other factors like | ||
| /// what architecture you're compiling *from*. | ||
| /// | ||
| /// The hashing just uses the standard `Hash` trait, but the implementations of | ||
| /// `Hash` for the `usize` and `isize` types are *not* architecture independent | ||
| /// (e.g. they has 4 or 8 bytes). As a result we want to avoid `usize` and | ||
| /// `isize` completely when hashing. | ||
| /// | ||
| /// To do that, we encode all integers to be hashed with some | ||
| /// arch-independent encoding. | ||
| /// | ||
| /// At the moment, we pass i8/u8 straight through and encode | ||
| /// all other integers using leb128. | ||
| /// | ||
| /// This hasher currently always uses the stable Blake2b algorithm | ||
| /// and allows for variable output lengths through its type | ||
| /// parameter. | ||
| #[derive(Debug)] | ||
| pub struct StableHasher<W> { | ||
| state: Blake2bHasher, | ||
| bytes_hashed: u64, | ||
| width: PhantomData<W>, | ||
| } | ||
|
|
||
| pub trait StableHasherResult: Sized { | ||
| fn finish(hasher: StableHasher<Self>) -> Self; | ||
| } | ||
|
|
||
| impl<W: StableHasherResult> StableHasher<W> { | ||
| pub fn new() -> Self { | ||
| StableHasher { | ||
| state: Blake2bHasher::new(mem::size_of::<W>(), &[]), | ||
| bytes_hashed: 0, | ||
| width: PhantomData, | ||
| } | ||
| } | ||
|
|
||
| pub fn finish(self) -> W { | ||
| W::finish(self) | ||
| } | ||
| } | ||
|
|
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| impl StableHasherResult for [u8; 20] { | ||
| fn finish(mut hasher: StableHasher<Self>) -> Self { | ||
| let mut result: [u8; 20] = [0; 20]; | ||
| result.copy_from_slice(hasher.state.finalize()); | ||
| result | ||
| } | ||
| } | ||
|
|
||
| impl StableHasherResult for u64 { | ||
| fn finish(mut hasher: StableHasher<Self>) -> Self { | ||
| hasher.state.finalize(); | ||
| hasher.state.finish() | ||
| } | ||
| } | ||
|
|
||
| impl<W> StableHasher<W> { | ||
| #[inline] | ||
| pub fn finalize(&mut self) -> &[u8] { | ||
| self.state.finalize() | ||
| } | ||
|
|
||
| #[inline] | ||
| pub fn bytes_hashed(&self) -> u64 { | ||
| self.bytes_hashed | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write_uleb128(&mut self, value: u64) { | ||
| let mut buf = [0; 16]; | ||
| let len = write_unsigned_leb128_to_buf(&mut buf, value); | ||
| self.state.write(&buf[..len]); | ||
| self.bytes_hashed += len as u64; | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write_ileb128(&mut self, value: i64) { | ||
| let mut buf = [0; 16]; | ||
| let len = write_signed_leb128_to_buf(&mut buf, value); | ||
| self.state.write(&buf[..len]); | ||
| self.bytes_hashed += len as u64; | ||
| } | ||
| } | ||
|
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| // For the non-u8 integer cases we leb128 encode them first. Because small | ||
| // integers dominate, this significantly and cheaply reduces the number of | ||
| // bytes hashed, which is good because blake2b is expensive. | ||
| impl<W> Hasher for StableHasher<W> { | ||
| fn finish(&self) -> u64 { | ||
| panic!("use StableHasher::finish instead"); | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write(&mut self, bytes: &[u8]) { | ||
| self.state.write(bytes); | ||
| self.bytes_hashed += bytes.len() as u64; | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write_u8(&mut self, i: u8) { | ||
| self.state.write_u8(i); | ||
| self.bytes_hashed += 1; | ||
| } | ||
|
|
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| #[inline] | ||
| fn write_u16(&mut self, i: u16) { | ||
| self.write_uleb128(i as u64); | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write_u32(&mut self, i: u32) { | ||
| self.write_uleb128(i as u64); | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write_u64(&mut self, i: u64) { | ||
| self.write_uleb128(i); | ||
| } | ||
|
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| #[inline] | ||
| fn write_usize(&mut self, i: usize) { | ||
| self.write_uleb128(i as u64); | ||
| } | ||
|
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||
| #[inline] | ||
| fn write_i8(&mut self, i: i8) { | ||
| self.state.write_i8(i); | ||
| self.bytes_hashed += 1; | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write_i16(&mut self, i: i16) { | ||
| self.write_ileb128(i as i64); | ||
| } | ||
|
|
||
| #[inline] | ||
| fn write_i32(&mut self, i: i32) { | ||
| self.write_ileb128(i as i64); | ||
| } | ||
|
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| #[inline] | ||
| fn write_i64(&mut self, i: i64) { | ||
| self.write_ileb128(i); | ||
| } | ||
|
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||
| #[inline] | ||
| fn write_isize(&mut self, i: isize) { | ||
| self.write_ileb128(i as i64); | ||
| } | ||
| } |
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