src/librustc_back/target/thumb_base.rs

   1 // Copyright 2016 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // These 4 `thumbv*` targets cover the ARM Cortex-M family of processors which are widely used in
  12 // microcontrollers. Namely, all these processors:
  13 //
  14 // - Cortex-M0
  15 // - Cortex-M0+
  16 // - Cortex-M1
  17 // - Cortex-M3
  18 // - Cortex-M4(F)
  19 // - Cortex-M7(F)
  20 //
  21 // We have opted for 4 targets instead of one target per processor (e.g. `cortex-m0`, `cortex-m3`,
  22 // etc) because the differences between some processors like the cortex-m0 and cortex-m1 are almost
  23 // non-existent from the POV of codegen so it doesn't make sense to have separate targets for them.
  24 // And if differences exist between two processors under the same target, rustc flags can be used to
  25 // optimize for one processor or the other.
  26 //
  27 // Also, we have not chosen a single target (`arm-none-eabi`) like GCC does because this makes
  28 // difficult to integrate Rust code and C code. Targeting the Cortex-M4 requires different gcc flags
  29 // than the ones you would use for the Cortex-M0 and with a single target it'd be impossible to
  30 // differentiate one processor from the other.
  31 //
  32 // About arm vs thumb in the name. The Cortex-M devices only support the Thumb instruction set,
  33 // which is more compact (higher code density), and not the ARM instruction set. That's why LLVM
  34 // triples use thumb instead of arm. We follow suit because having thumb in the name let us
  35 // differentiate these targets from our other `arm(v7)-*-*-gnueabi(hf)` targets in the context of
  36 // build scripts / gcc flags.
  37
  38 use PanicStrategy;
  39 use std::default::Default;
  40 use target::TargetOptions;
  41
  42 pub fn opts() -> TargetOptions {
  43     // See rust-lang/rfcs#1645 for a discussion about these defaults
  44     TargetOptions {
  45         executables: true,
  46         // In 99%+ of cases, we want to use the `arm-none-eabi-gcc` compiler (there aren't many
  47         // options around)
  48         linker: "arm-none-eabi-gcc".to_string(),
  49         // Because these devices have very little resources having an unwinder is too onerous so we
  50         // default to "abort" because the "unwind" strategy is very rare.
  51         panic_strategy: PanicStrategy::Abort,
  52         // Similarly, one almost always never wants to use relocatable code because of the extra
  53         // costs it involves.
  54         relocation_model: "static".to_string(),
  55         abi_blacklist: super::arm_base::abi_blacklist(),
  56         .. Default::default()
  57     }
  58 }