1 // These `thumbv*` targets cover the ARM Cortex-M family of processors which are widely used in
2 // microcontrollers. Namely, all these processors:
13 // We have opted for these instead of one target per processor (e.g., `cortex-m0`, `cortex-m3`,
14 // etc) because the differences between some processors like the cortex-m0 and cortex-m1 are almost
15 // non-existent from the POV of codegen so it doesn't make sense to have separate targets for them.
16 // And if differences exist between two processors under the same target, rustc flags can be used to
17 // optimize for one processor or the other.
19 // Also, we have not chosen a single target (`arm-none-eabi`) like GCC does because this makes
20 // difficult to integrate Rust code and C code. Targeting the Cortex-M4 requires different gcc flags
21 // than the ones you would use for the Cortex-M0 and with a single target it'd be impossible to
22 // differentiate one processor from the other.
24 // About arm vs thumb in the name. The Cortex-M devices only support the Thumb instruction set,
25 // which is more compact (higher code density), and not the ARM instruction set. That's why LLVM
26 // triples use thumb instead of arm. We follow suit because having thumb in the name let us
27 // differentiate these targets from our other `arm(v7)-*-*-gnueabi(hf)` targets in the context of
28 // build scripts / gcc flags.
30 use crate::spec::{Cc, FramePointer, LinkerFlavor, Lld, PanicStrategy, RelocModel, TargetOptions};
32 pub fn opts() -> TargetOptions {
33 // See rust-lang/rfcs#1645 for a discussion about these defaults
35 linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
36 // In most cases, LLD is good enough
37 linker: Some("rust-lld".into()),
38 // Because these devices have very little resources having an unwinder is too onerous so we
39 // default to "abort" because the "unwind" strategy is very rare.
40 panic_strategy: PanicStrategy::Abort,
41 // Similarly, one almost always never wants to use relocatable code because of the extra
43 relocation_model: RelocModel::Static,
44 // When this section is added a volatile load to its start address is also generated. This
45 // volatile load is a footgun as it can end up loading an invalid memory address, depending
46 // on how the user set up their linker scripts. This section adds pretty printer for stuff
47 // like std::Vec, which is not that used in no-std context, so it's best to left it out
48 // until we figure a way to add the pretty printers without requiring a volatile load cf.
49 // rust-lang/rust#44993.
50 emit_debug_gdb_scripts: false,
51 // LLVM is eager to trash the link register when calling `noreturn` functions, which
52 // breaks debugging. Preserve LR by default to prevent that from happening.
53 frame_pointer: FramePointer::Always,
54 // ARM supports multiple ABIs for enums, the linux one matches the default of 32 here
55 // but any arm-none or thumb-none target will be defaulted to 8 on GCC and clang