Rewrite the linking section of "A Freestanding Rust Binary" #577
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See #577 for information about the rewrite. This commit updates the azure pipelines CI script in the following way: - build on all three OSs - build for thumbv7em-none-eabihf
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- solve linker errors by compiling for thumbv7em-none-eabihf - make old section about linker arguments optional content - use different linker arguments on Windows and macOS to use the `_start` entry point on all OSs - Add an (optional) section that explains how to set linker arguments in .cargo/config - Add an (optional) section that discourages the linker arguments approach and recommends the `#[start]` attribute instead - reorganize section levels
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See #577 for information about the rewrite. This commit updates the azure pipelines CI script in the following way: - build on all three OSs - build for thumbv7em-none-eabihf
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This pull request rewrites the section about overwriting the entry point. Instead of recommending to pass platform-specific arguments to the linker, the post now solves the linker errors by compiling for the bare metal
thumbv7em-none-eabihftarget. This makes much more sense, since it is the same approach that we use in the second post (by using a custom bare metal target).We keep the old section about the platform specific linker arguments, but perform the following changes:
cargo buildat the end of the post – is now achieved by building forthumbv7em-none-eabihf, so we no longer need it for bringing the post to an end.src/main.rs, we now use_starton these platforms as well by explicitly overriding the entry point name.mainCRTStartupandmainon Windows, we now specifcy the subsystem explicitly. Thus we no longer need to create a function namedmainso that the linker can infer a default subsystem.Systemlibrary on macOS, we force a static binary by passing-staticand-nostartfiles.rustflagskeys in a.cargo/configfile.#[start]attribute forno_stdbinaries that should run on top of existing OSs.Further, this PR reorganize section levels so that we have more top level sections instead of keeping everything in the "Disabling the Standard Library" section.
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post-01branch: #578