[meta] update MSRV to 1.75, turn on asm support unconditionally (#267)

There were a lot of build flags working around asm incompatibilities. Now that
inline asm has been stable for a while, we can rip it all out.

Also update the MSRV to 1.75.

Author: sunshowers

Cargo.lock

@@ -225,58 +225,6 @@ comes with significant tradeoffs. As such the current recommendation is:
 function calling it), and document to their users that this function should be called to
 guarantee that probes are registered.
 
-## Notes
-
-The `usdt` crate requires [inline asm][inline-asm], a feature stabilized in Rust 1.59.
-Prior to that version, a nightly toolchain was required to import the feature.  For legacy
-convenience reasons, the crate contains also an empty, no-op implementation, which generates all the
-same probe macros, but with empty bodies (thus not requiring inline asm).  This may be selected by
-passing the `--no-default-features` flag when building the crate, or by using `default-features =
-false` in the [`[dependencies]` table][feature-deps] of one's `Cargo.toml`.
-
-Library developers may use `usdt` as an optional dependency, gated by a feature, for example
-named `usdt-probes` or similar. This feature would imply the `usdt/asm` feature, but the `usdt`
-crate could be used with the no-op implementation by default. For example, your `Cargo.toml`
-might contain
-
-```
-[dependencies]
-usdt = { version = "*", optional = true, default-features = false }
-
-# ... later
-
-[features]
-usdt-probes = ["usdt/asm"]
-```
-
-This allows users to opt into probes if they are using a suitably new toolchain, or and older
-nightly with the `asm` feature enabled on their project.
-
-### The Rust `asm` feature
-
-On toolchains prior to 1.59, inline asm was [not available][asm-issue] without the feature being
-enabled.  This applies to code _calling_ the probe macros, in addition to `usdt` where they are
-implemented.  Those generated probe macros must be in a module that is either built with a >=1.59
-toolchain or where the `feature(asm)` configuration is present.
-
-
-#### Toolchain versions and the `asm_sym` feature
-
-On macOS (where the linker is involved in USDT probe creation) on toolchains prior to 1.66, the
-`asm_sym` feature is required (in addition to `asm` in nightly toolchains prior to November 2021;
-see [this issue][asm-feature-flags]). For such a toolchain, this feature can be included just on
-macOS e.g., with `#![cfg_attr(target_os = "macos", feature(asm_sym))]`, or unconditionally on all
-platforms.
-
-The addition of the `asm_sym` feature presents an unfortunate problem. It is no longer possible to
-compile the `usdt` crate (or any crate defining probes) with a toolchain from before that feature
-was added _and_ after its addition. In the former case, we'd get errors about an unknown feature
-should we include the `asm_sym` feature, and we'd get errors about functionality behind a feature
-gate from later compilers should we omit the feature.
-
-Fortunately with the stabilization of `asm_sym` in 1.66, using this crate should become much
-simpler.
-
 ## References
 
 [1]: https://illumos.org/books/dtrace/chp-usdt.html#chp-usdt
@@ -285,7 +233,3 @@ simpler.
 [4]: https://docs.rs/serde_json/1.0.68/serde_json/fn.to_string.html
 [serde-json-error]: https://docs.serde.rs/serde_json/error/struct.Error.html
 [serde-runtime-fail]: https://github.com/serde-rs/serde/issues/1307
-[inline-asm]: https://github.com/rust-lang/rust/issues/72016
-[feature-deps]: https://doc.rust-lang.org/cargo/reference/features.html#dependency-features
-[asm-issue]: https://github.com/rust-lang/rust/issues/72016
-[asm-feature-flags]: https://github.com/rust-lang/rust/pull/90348

README.md

@@ -10,5 +10,5 @@ publish = false
 [dependencies]
 clap = { version = "4.5.11", features = ["derive"] }
 dof = { path = "../dof", features = ["des"] }
-usdt = { path = "../usdt", features = ["asm"] }
+usdt = { path = "../usdt" }
 usdt-impl = { path = "../usdt-impl", features = ["des"] }

common-build.rs

@@ -7,10 +7,3 @@ publish = false
 [dependencies]
 usdt = { path = "../usdt", default-features = false }
 serde = "1"
-
-[build-dependencies]
-version_check = "0.9.5"
-
-[features]
-default = ["asm"]
-asm = ["usdt/asm"]

dusty/Cargo.toml

@@ -15,9 +15,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![cfg_attr(usdt_need_feat_asm, feature(asm))]
-#![cfg_attr(usdt_need_feat_asm_sym, feature(asm_sym))]
-
 use serde::Serialize;
 
 /// By deriving the `serde::Serialize` trait, the `Arg` struct can be used as an argument to a

probe-test-attr/Cargo.toml

@@ -9,8 +9,3 @@ usdt = { path = "../usdt", default-features = false }
 
 [build-dependencies]
 usdt = { path = "../usdt" }
-version_check = "0.9.5"
-
-[features]
-default = ["asm"]
-asm = ["usdt/asm"]

probe-test-attr/src/main.rs

@@ -17,16 +17,6 @@ use usdt::Builder;
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
 
-    if !version_check::is_min_version("1.59").unwrap_or(false) {
-        println!("cargo:rustc-cfg=usdt_need_feat_asm");
-    }
-    #[cfg(target_os = "macos")]
-    if version_check::supports_feature("asm_sym").unwrap_or(false)
-        && !version_check::is_min_version("1.67").unwrap_or(false)
-    {
-        println!("cargo:rustc-cfg=usdt_need_feat_asm_sym");
-    }
-
     println!("cargo:rerun-if-changed=test.d");
     Builder::new("test.d").build().unwrap();
 }

probe-test-build/Cargo.toml

@@ -14,9 +14,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![cfg_attr(usdt_need_feat_asm, feature(asm))]
-#![cfg_attr(usdt_need_feat_asm_sym, feature(asm_sym))]
-
 use std::thread::sleep;
 use std::time::Duration;
 

probe-test-build/build.rs

@@ -6,10 +6,3 @@ publish = false
 
 [dependencies]
 usdt = { path = "../usdt", default-features = false }
-
-[build-dependencies]
-version_check = "0.9.5"
-
-[features]
-default = ["asm"]
-asm = ["usdt/asm"]

probe-test-build/src/main.rs

@@ -14,9 +14,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![cfg_attr(usdt_need_feat_asm, feature(asm))]
-#![cfg_attr(usdt_need_feat_asm_sym, feature(asm_sym))]
-
 use std::thread::sleep;
 use std::time::Duration;
 

probe-test-macro/Cargo.toml

@@ -7,6 +7,3 @@ publish = false
 [dependencies]
 usdt = { path = "../../usdt" }
 serde = "1"
-
-[build-dependencies]
-version_check = "0.9.5"

probe-test-macro/src/main.rs

@@ -15,8 +15,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![cfg_attr(usdt_need_feat_asm, feature(asm))]
-#![cfg_attr(usdt_need_feat_asm_sym, feature(asm_sym))]
 use serde::Serialize;
 
 /// Most struct or tuple types implementing serde::Serialize may be used in probes.

tests/argument-types/Cargo.toml

@@ -11,6 +11,3 @@ serde_json = "*"
 
 [dev-dependencies]
 trybuild = "1.0.98"
-
-[build-dependencies]
-version_check = "0.9.5"

tests/argument-types/src/main.rs

@@ -10,4 +10,3 @@ usdt-tests-common = { path = "../../usdt-tests-common" }
 
 [build-dependencies]
 usdt = { path = "../../usdt" }
-version_check = "0.9.5"

tests/compile-errors/Cargo.toml

@@ -17,16 +17,6 @@ use usdt::Builder;
 fn main() {
     println!("cargo:rerun-if-changed=build.rs");
 
-    if !version_check::is_min_version("1.59").unwrap_or(false) {
-        println!("cargo:rustc-cfg=usdt_need_feat_asm");
-    }
-    #[cfg(target_os = "macos")]
-    if version_check::supports_feature("asm_sym").unwrap_or(false)
-        && !version_check::is_min_version("1.67").unwrap_or(false)
-    {
-        println!("cargo:rustc-cfg=usdt_need_feat_asm_sym");
-    }
-
     println!("cargo:rerun-if-changed=test.d");
     Builder::new("test.d").build().unwrap();
 }

tests/does-it-work/Cargo.toml

@@ -16,8 +16,6 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#![cfg_attr(usdt_need_feat_asm, feature(asm))]
-#![cfg_attr(usdt_need_feat_asm_sym, feature(asm_sym))]
 #![allow(non_snake_case)]
 
 use usdt::register_probes;

tests/does-it-work/build.rs

@@ -11,10 +11,3 @@ default-features = false
 [build-dependencies.usdt]
 path = "../../usdt"
 default-features = false
-
-[build-dependencies]
-version_check = "0.9.5"
-
-[features]
-default = ["asm"]
-asm = ["usdt/asm"]