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Note warning of default features on libc #34132

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Merged
merged 2 commits into from
Jun 12, 2016
Merged

Note warning of default features on libc #34132

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299a1a0
Note warning of default features on libc
AtheMathmo Jun 7, 2016
8844fd4
Adding sections and brief explanation of libc
AtheMathmo Jun 7, 2016
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24 changes: 20 additions & 4 deletions src/doc/book/no-stdlib.md
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Expand Up @@ -12,9 +12,26 @@ don’t want to use the standard library via an attribute: `#![no_std]`.
> `#![no_std]`](using-rust-without-the-standard-library.html)

Obviously there's more to life than just libraries: one can use
`#[no_std]` with an executable, controlling the entry point is
possible in two ways: the `#[start]` attribute, or overriding the
default shim for the C `main` function with your own.
`#[no_std]` with an executable.

### Using libc

In order to build a `#[no_std]` executable we will need libc as a dependency. We can specify
this using our `Cargo.toml` file:

```toml
[dependencies]
libc = { version = "0.2.11", default-features = false }
```

Note that the default features have been disabled. This is a critical step -
**the default features of libc include the standard library and so must be
disabled.**

### Writing an executable without stdlib

Controlling the entry point is possible in two ways: the `#[start]` attribute,
or overriding the default shim for the C `main` function with your own.

The function marked `#[start]` is passed the command line parameters
in the same format as C:
Expand Down Expand Up @@ -72,7 +89,6 @@ pub extern fn main(argc: i32, argv: *const *const u8) -> i32 {
# // fn main() {} tricked you, rustdoc!
```


The compiler currently makes a few assumptions about symbols which are available
in the executable to call. Normally these functions are provided by the standard
library, but without it you must define your own.
Expand Down