Troubleshooting 'cargo Build --release --features Runtime-benchmarks'
Navigating the world of blockchain development, especially within the robust ecosystem of Polkadot and its SDK, often involves diving deep into performance optimization. One of the key commands for this is cargo build --release --features runtime-benchmarks. However, sometimes, this process can hit a snag, leaving developers with errors like the one you've encountered: Failed to run 'cargo build --release --features runtime-benchmarks'. This isn't just a roadblock; it's an opportunity to understand the inner workings of your build process and how to resolve common issues. Let's break down this error, understand its implications, and walk through the steps to get your benchmarks running smoothly.
The core of the problem often lies in the detailed specifications required for cross-compilation or specific target architectures. When you invoke cargo build --release --features runtime-benchmarks, you're not just compiling your code; you're instructing Cargo to build with optimizations (--release) and to include specific features (runtime-benchmarks) that are crucial for generating performance metrics for your runtime logic. These benchmarks are invaluable for understanding how your Substrate-based chain will perform under various conditions and for identifying potential bottlenecks before deployment. The error message, specifically the part indicating error: failed to run 'rustc' to learn about target-specific information, points towards an issue where the Rust compiler itself is struggling to understand the target environment you're trying to build for. This often happens when the target definition file, which tells rustc about the architecture, instruction set, and other specifics of the target system, is malformed or incorrectly parsed. The subsequent error: error loading target specification: target-pointer-width: invalid type: string "64", expected u16 at line 16 column 30 is the smoking gun. It tells us that the rustc compiler encountered a problem while parsing the target specification file, specifically expecting a numerical value for target-pointer-width but finding a string instead. This is a critical detail, as the pointer width is fundamental to how memory addresses are handled on a given architecture. For example, a 64-bit architecture uses 64-bit pointers. The file mentioned, often related to polkavm-linker, suggests that you might be attempting to build for a specific virtual machine or an embedded target, which requires precise configuration.
Decoding the Error Message: A Deep Dive
Let's dissect the error message you received: Failed to run "cargo build --release --features runtime-benchmarks". This is the top-level command that initiated the build process. The subsequent lines provide the crucial context. The Caused by: process didn't exit successfully: ... (exit status: 1) indicates that a subprocess, in this case, the build script for pallet-revive-fixtures, failed to complete its execution. The stdout and stderr sections are where the real clues lie. The stdout shows cargo::rerun-if-env-changed and cargo::rerun-if-changed directives. These are Cargo's mechanisms to determine if a build script needs to be re-executed. They're generally not the source of the error but indicate what triggered the build script to run in the first place. The real culprit is in the stderr. Here, we see error: failed to run 'rustc' to learn about target-specific information. This clearly states that the Rust compiler couldn't get the necessary details about the target you're building for. The nested Caused by: process didn't exit successfully: ... - --print=file-names -Dwarnings --target ... shows that rustc was invoked with specific arguments, including a custom target file path (/Users/xxxx/Library/Caches/.polkavm-linker/0.29.0/riscv64emac-unknown-none-polkavm.json). This custom target file is where the error originates.
The most revealing part is error: error loading target specification: target-pointer-width: invalid type: string "64", expected u16 at line 16 column 30. This pinpointed the exact issue: within the target specification file (likely the .json file related to Polkavm), at line 16, column 30, there's a mismatch. The target-pointer-width field, which should be a 16-bit unsigned integer (u16), was found to be a string literal "64". This is a configuration error in the target definition itself. When rustc tries to load this file to understand the target environment, it encounters this type mismatch and fails. The help: run ustc --print target-list or a list of built-in targets is a standard suggestion from rustc when it encounters target-related problems, but in this case, it's less about missing a built-in target and more about an incorrectly configured custom target.
Resolving the target-pointer-width Error
The immediate cause of the target-pointer-width error is a malformed JSON in the target specification file. This file is responsible for defining the characteristics of the target architecture, such as its CPU, operating system, and ABI. The target-pointer-width parameter specifies the size of a pointer in bits on that architecture. For a 64-bit architecture, this should be 64. However, the error indicates that it's being interpreted as a string `
