Update BLST, add force-adx support (#1595)

## Issue Addressed

Closes #1504
Closes https://github.com/sigp/lighthouse/issues/1505

## Proposed Changes

* Update `blst` to the latest version, which is more portable and includes finer-grained compilation controls (see below).
* Detect the case where a binary has been explicitly compiled with ADX support but it's missing at runtime, and report a nicer error than `SIGILL`.

## Known Issues

* None. The previous issue with `make build-aarch64` (https://github.com/supranational/blst/issues/27), has been resolved.

## Additional Info

I think we should tweak our release process and our Docker builds so that we provide two options:

Binaries:

* `lighthouse`: compiled with `modern`/`force-adx`, for CPUs 2013 and newer
* `lighthouse-portable`: compiled with `portable` for older CPUs

Docker images:

* `sigp/lighthouse:latest`: multi-arch image with `modern` x86_64 and vanilla aarch64 binary
* `sigp/lighthouse:latest-portable`: multi-arch image with `portable` builds for x86_64 and aarch64

And relevant Docker images for the releases (as per https://github.com/sigp/lighthouse/pull/1574#issuecomment-687766141), tagged `v0.x.y` and `v0.x.y-portable`

Cargo.lock

@@ -525,7 +525,7 @@ dependencies = [
 [[package]]
 name = "blst"
 version = "0.1.1"
-source = "git+https://github.com/sigp/blst.git?rev=284f7059642851c760a09fb1708bcb59c7ca323c#284f7059642851c760a09fb1708bcb59c7ca323c"
+source = "git+https://github.com/supranational/blst.git?rev=a8398ed284b0d78858302ad1ceb25a80e7bbe535#a8398ed284b0d78858302ad1ceb25a80e7bbe535"
 dependencies = [
  "cc",
  "glob",

book/src/cross-compiling.md

@@ -18,17 +18,15 @@ project.
 
 The `Makefile` in the project contains four targets for cross-compiling:
 
-- `build-x86_64`: builds an optimized version for x86_64 processors (suitable
-	for most users).
-- `build-x86_64-portable`: builds a version x86_64 processors which avoids
-	using some modern CPU instructions that might cause an "illegal
-	instruction" error on older CPUs.
-- `build-aarch64`: builds an optimized version for 64bit ARM processors
+- `build-x86_64`: builds an optimized version for x86_64 processors (suitable for most users).
+  Supports Intel Broadwell (2014) and newer, and AMD Ryzen (2017) and newer.
+- `build-x86_64-portable`: builds a version for x86_64 processors which avoids using some modern CPU
+  instructions that are incompatible with older CPUs. Suitable for pre-Broadwell/Ryzen CPUs.
+- `build-aarch64`: builds an optimized version for 64-bit ARM processors
 	(suitable for Raspberry Pi 4).
-- `build-aarch64-portable`: builds a version 64 bit ARM processors which avoids
-	using some modern CPU instructions that might cause an "illegal
-	instruction" error on older CPUs.
-
+- `build-aarch64-portable`: builds a version for 64-bit ARM processors which avoids using some
+  modern CPU instructions. In practice, very few ARM processors lack the instructions necessary to
+  run the faster non-portable build.
 
 ### Example
 

crypto/bls/Cargo.toml

@@ -17,7 +17,7 @@ eth2_hashing = "0.1.0"
 ethereum-types = "0.9.1"
 arbitrary = { version = "0.4.4", features = ["derive"], optional = true }
 zeroize = { version = "1.0.0", features = ["zeroize_derive"] }
-blst = { git = "https://github.com/sigp/blst.git", rev = "284f7059642851c760a09fb1708bcb59c7ca323c" }
+blst = { git = "https://github.com/supranational/blst.git", rev = "a8398ed284b0d78858302ad1ceb25a80e7bbe535" }
 
 [features]
 default = ["supranational"]
@@ -25,3 +25,4 @@ fake_crypto = []
 milagro = []
 supranational = []
 supranational-portable = ["supranational", "blst/portable"]
+supranational-force-adx = ["supranational", "blst/force-adx"]

lighthouse/Cargo.toml

@@ -9,6 +9,9 @@ edition = "2018"
 write_ssz_files = ["beacon_node/write_ssz_files"]
 # Compiles the BLS crypto code so that the binary is portable across machines.
 portable = ["bls/supranational-portable"]
+# Compiles BLST so that it always uses ADX instructions.
+# Compatible with processors from 2013 onwards.
+modern = ["bls/supranational-force-adx"]
 # Uses the slower Milagro BLS library, which is written in native Rust.
 milagro = ["bls/milagro"]
 

lighthouse/src/main.rs

@@ -16,6 +16,8 @@ pub const ETH2_CONFIG_FILENAME: &str = "eth2-spec.toml";
 fn bls_library_name() -> &'static str {
     if cfg!(feature = "portable") {
         "blst-portable"
+    } else if cfg!(feature = "modern") {
+        "blst-modern"
     } else if cfg!(feature = "milagro") {
         "milagro"
     } else {
@@ -181,6 +183,13 @@ fn run<E: EthSpec>(
         ));
     }
 
+    #[cfg(all(feature = "modern", target_arch = "x86_64"))]
+    if !std::is_x86_feature_detected!("adx") {
+        return Err(format!(
+            "CPU incompatible with optimized binary, please try Lighthouse portable build"
+        ));
+    }
+
     let debug_level = matches
         .value_of("debug-level")
         .ok_or_else(|| "Expected --debug-level flag".to_string())?;