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Fix thumbv4t-none-eabi frame pointer setting #99227

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merged 7 commits into from
Jul 30, 2022
Merged

Fix thumbv4t-none-eabi frame pointer setting #99227

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86ab4a0
word-wrap the comments.
Lokathor Jul 14, 2022
7be0b87
Update thumbv4t_none_eabi.rs
Lokathor Jul 14, 2022
6c22b44
add missing imports.
Lokathor Jul 14, 2022
0e78c73
conform to the tidy expectations
Lokathor Jul 14, 2022
26e0787
tidy demands this whitespace go away
Lokathor Jul 14, 2022
9cf5b2d
Update thumbv4t_none_eabi.rs
Lokathor Jul 28, 2022
2eac6f3
once again tidy was unhappy
Lokathor Jul 28, 2022
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23 changes: 19 additions & 4 deletions compiler/rustc_target/src/spec/thumbv4t_none_eabi.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,11 +4,19 @@
//!
//! Please ping @Lokathor if changes are needed.
//!
//! This target profile assumes that you have the ARM binutils in your path (specifically the linker, `arm-none-eabi-ld`). They can be obtained for free for all major OSes from the ARM developer's website, and they may also be available in your system's package manager. Unfortunately, the standard linker that Rust uses (`lld`) only supports as far back as `ARMv5TE`, so we must use the GNU `ld` linker.
//! This target profile assumes that you have the ARM binutils in your path
//! (specifically the linker, `arm-none-eabi-ld`). They can be obtained for free
//! for all major OSes from the ARM developer's website, and they may also be
//! available in your system's package manager. Unfortunately, the standard
//! linker that Rust uses (`lld`) only supports as far back as `ARMv5TE`, so we
//! must use the GNU `ld` linker.
//!
//! **Important:** This target profile **does not** specify a linker script. You just get the default link script when you build a binary for this target. The default link script is very likely wrong, so you should use `-Clink-arg=-Tmy_script.ld` to override that with a correct linker script.
//! **Important:** This target profile **does not** specify a linker script. You
//! just get the default link script when you build a binary for this target.
//! The default link script is very likely wrong, so you should use
//! `-Clink-arg=-Tmy_script.ld` to override that with a correct linker script.

use crate::spec::{cvs, LinkerFlavor, Target, TargetOptions};
use crate::spec::{cvs, LinkerFlavor, PanicStrategy, RelocModel, Target, TargetOptions};

pub fn target() -> Target {
Target {
Expand Down Expand Up @@ -39,13 +47,20 @@ pub fn target() -> Target {
// minimum extra features, these cannot be disabled via -C
features: "+soft-float,+strict-align".into(),

panic_strategy: PanicStrategy::Abort,
relocation_model: RelocModel::Static,
// suggested from thumb_base, rust-lang/rust#44993.
emit_debug_gdb_scripts: false,
// suggested from thumb_base, with no-os gcc/clang use 8-bit enums
c_enum_min_bits: 8,

main_needs_argc_argv: false,

// don't have atomic compare-and-swap
atomic_cas: false,
has_thumb_interworking: true,

..super::thumb_base::opts()
..Default::default()
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I'm a little surprised from the PR description that this doesn't just manually set the frame pointer to "may omit" which thumb_base gets wrong for this specific target, but instead decides not to use thumb_base at all.

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Somehow that didn't even occur to me compared to "give me the real defaults".

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I think I'd prefer to see it still use thumb_base and override the changed field, rather than this approach. Unless there's a reason why this specific target is likely to diverge from thumb_base more often than not. I'm not super familiar with what we normally do for target specifications though, so others may disagree.

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I can set the field here, but either way I'd prefer to not use thumb_base. Then as the target maintainer i have to try and pay attention to changes to an additional thing. Also as a user a person would have to look in 3 places instead of just 2 to understand all the details.

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That's understandable, but at the same time, if there is a change to thumb_base that would be applicable here then it could easily be missed. Ultimately, this is a trade-off that's inherent to how we define these target specs, and I'm not sure it makes sense to be inconsistent about inheriting from base specs on the basis of the preference of the target maintainer, but I don't feel strongly about this. I'd like to see what others think.

},
}
}