14 ms·

32Kb with the following configuration, on a linux target. It's not the default, you're using nightly, it's more complex to build and there are tradeoffs. You ca

32Kb with the following configuration, on a linux target. It's not the default, you're using nightly, it's more complex to build and there are tradeoffs. You can even go less than that if that's your thing [profile.release] strip = true opt-level = "z" lto = true codegen-units = 1 panic = "abort" cargo +nightly build -Z build-std=std,panic_abort -Z build-std-features=panic_immediate_abort --target x86_64-unknown-linux-gnu --release As mentioned in another thread, I've simply followed https://github.com/johnthagen/min-sized-rust https://github.com/johnthagen/min-sized-rust

flohofwoe 3y ago
These look like sensible defaults to me for release mode. What are the tradeoffs?
- rfoo 3y ago
  opt-level = "z" may be slightly slower than O2/O3. lto = true and lto-units = 1 makes the final linking unbearably slow for large programs. These are still okay, but then `panic = "abort"` shakes a lot of code off by making the final executable unable to print a nice stack trace (even without symbols) and instead immediately traps/abort()-s. Edit: and GP also used "panic-immediate-abort", which also removes the dependency to std::fmt::format!() because it now silently abort()s without even printing an error string.
  - exDM69 3y ago
    Additionally the panic = "abort" disables stack unwinding, and running destructors when panic occurs, so it's a big change to the semantics of the program. It's comparable to C++ land -fno-exceptions (not exactly, but similar).
    - junon 3y ago
      Abort panic strategy is common in firmware and osdev, for anyone wondering if there are other use cases.
    - flohofwoe 3y ago
      IMHO when a piece of code decides to panic it should only happen when execution cannot continue under any circumstances, and in such cases all bets are off whether any cleanup code would actually still work. A hard abort might indeed be the best option.
      - edflsafoiewq 3y ago
        That seems overly pessimistic (or perhaps overly optimistic about code that does not panic). Panics mostly exist to guard code from entering into such unrecoverable states, eg writing past the end of an array.
        flohofwoe 3y ago
        For me the difference would be: if the write past the array has been detected before it happens (via a range check) it would be a regular error which which can be handled, while a panic would be "oops somebody else has written past the end of the array" (e.g. a hitting a canary check), which should abort immediately because at that point it's no longer guaranteed that any recovery code would even work or just make things worse (e.g. trying to flush data from memory back to disk, but that data might have been corrupted too).
        lifthrasiir 3y ago
        You have a good point and lock poisoning had the same reasoning, but wasn't really popular [1]. (In hindsight the poisoning itself was a great idea but should have been decoupled from locks.) Compared to other languages with similar constructs, Rust panic is probably regarded as less fatal because an incorrect but safe Rust code tends to have a limited reach. Ah, and it should be also noted that some non-fatal signals were also delivered only via panic. The best-known example is a memory allocation failure, which is recoverable in Rust but needed unwinding for a long time. Nowadays you have an unsafe but non-unwinding alternative. [1] https://blog.rust-lang.org/2020/12/11/lock-poisoning-survey.html https://blog.rust-lang.org/2020/12/11/lock-poisoning-survey....
        edflsafoiewq 3y ago
  - josephg 3y ago
    > These are still okay, but then `panic = "abort"` shakes a lot of code off by making the final executable unable to print a nice stack trace (even without symbols) and instead immediately traps/abort()-s. I just tried this. The stack traces on panic seem more or less the same with or without panic = "abort" in Cargo.toml. For example, this program: fn main() { let v = vec![1, 2, 3]; v[99]; } Compiled with panic="abort" outputs this stack trace: $ RUST_BACKTRACE=1 cargo run --release Compiling rust-panic v0.1.0 (/Users/seph/temp/rust-panic) Finished release [optimized] target(s) in 1.82s Running `target/release/rust-panic` thread 'main' panicked at src/main.rs:4:6: index out of bounds: the len is 3 but the index is 99 stack backtrace: 0: _rust_begin_unwind 1: core::panicking::panic_fmt 2: core::panicking::panic_bounds_check 3: <alloc::vec::Vec<T,A> as core::ops::index::Index<I>>::index 4: rust_panic::main note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. [1] 95405 abort RUST_BACKTRACE=1 cargo run --release Weirdly, in this test if I don't strip the binary, I get a larger binary size with panic="abort" than when I leave that out. That is surely due to a bug somewhere.
    - ponkpanda 3y ago
      You're not adding the +nightly switch and the required flags to compiled std. Just setting panic=abort in cargo.toml isn't enough. One can get binaries pretty damn small (low-mid tens of kilobytes for a basic cli program doing something like hashing of a file). Problem I've found with manually compiling std (which has ancillary benefits of being able to compile to a specific uarch) is it can break the compilation process when bringing in third-party deps. The config.toml (stored in $PROJECT_ROOT/.cargo) overrides cargo's behaviour for all dependencies as well - which may break those compilations. Tbh, it's one reason I don't particularly rate the rustc+cargo toolchain - but for most people writing regular applications: just being able to do ```cargo build -r``` and not care about binary size, uarch optimization or custom llvm/rustc optimizations (PGO etc), most won't care.
  - lifthrasiir 3y ago
    > `panic = "abort"` shakes a lot of code off by making the final executable unable to print a nice stack trace (even without symbols) and instead immediately traps/abort()-s. I believe it does print backtraces then terminate, since the backtrace is printed via panic hooks, which happen before the actual unwinding.
    - vacuity 3y ago
      Is the backtrace performed by the OS and that's why it still works? And the debug info needs to still be provided, just not an unwinding mechanism?
- chrismorgan 3y ago
  opt-level z would not be a reasonable default: you should normally optimise for speed, not binary size. lto and codegen-units=1 have a huge compile time cost. For release for general distribution you should tend to favour them, but the release profile isn’t just about that activity (especially because debug/opt-level<2 is often just too slow to use while developing). You commonly want to create another profile for production distribution. Abort on panic changes runtime behaviour by stopping you from catching panics, which will completely break some programs, and harm the failure mode of others, so that e.g. one defective route on a web server will suddenly take the entire website down for everyone (or, if you have a supervisor that can restart the server, at least disrupt it for everyone).
  - flohofwoe 3y ago
    > you should normally optimise for speed, not binary size IME optimize for speed vs size usually isn't as clear cut as the name says though, sometimes smaller code does indeed run faster, but in most cases I've seen there's not much of a difference between -O3, -O2, -Os and -Oz.
    - kibwen 3y ago
      Weirdly, most of the time I find that -O3 produces smaller binaries than -Oz.
- lifthrasiir 3y ago
  Comparing with the current Cargo default [1]: • `panic = "abort"` means that any panic terminates the program. This is not always desirable because you may want to catch and recover from panics, particularly in long-running servers. • `strip = true` means that anything depending on DWARF would no longer work. Backtraces won't work, but also unwinding will no longer work (so this is disastrous if you haven't set `panic` above). The actual proposal has `strip = "debuginfo"` instead, so unwinding will work while backtraces won't. • `codegen-units = 1` is the number of concurrent compilation jobs (cgu) in the LLVM codegen phase. A single cgu will significantly increase the compilation time, while allowing a bit more optimization. Otherwise this is okay. • `lto = true` enables Rust-specific link-time optimizations across crates. The actual benefit depends on the set of crates linked, but it is significantly slower that many large enough projects wouldn't want it. It does benefit small programs like the "Hello, world" program the most though. • `opt-level = "z"` is same to C/C++ `-Oz` and the same pros and cons apply. [1] https://doc.rust-lang.org/cargo/reference/profiles.html#release https://doc.rust-lang.org/cargo/reference/profiles.html#rele...
  - flohofwoe 3y ago
    All makes sense, but I don't agree with: > This is not always desirable because you may want to catch and recover from panics, particularly in long-running servers. IMHO a panic implies that execution cannot continue under any circumstances, and even any attempts for a graceful shutdown might be futile (if recovery is possible it shouldn't be a panic but done through regular error handling). For a server process the best reaction to a panic would mean abort and clean restart. > A single cgu will significantly increase the compilation time, while allowing a bit more optimization. Increased build time is acceptable for release mode IMHO.
    - robinsonrc 3y ago
      I remember my disappointment when I found out panics could be “caught” and that I was still living in the world of exceptions
      - josephg 3y ago

flohofwoe 3y ago

These look like sensible defaults to me for release mode. What are the tradeoffs?

rfoo 3y ago
opt-level = "z" may be slightly slower than O2/O3. lto = true and lto-units = 1 makes the final linking unbearably slow for large programs. These are still okay, but then `panic = "abort"` shakes a lot of code off by making the final executable unable to print a nice stack trace (even without symbols) and instead immediately traps/abort()-s. Edit: and GP also used "panic-immediate-abort", which also removes the dependency to std::fmt::format!() because it now silently abort()s without even printing an error string.
- exDM69 3y ago
  Additionally the panic = "abort" disables stack unwinding, and running destructors when panic occurs, so it's a big change to the semantics of the program. It's comparable to C++ land -fno-exceptions (not exactly, but similar).
  - junon 3y ago
    Abort panic strategy is common in firmware and osdev, for anyone wondering if there are other use cases.
  - flohofwoe 3y ago
    IMHO when a piece of code decides to panic it should only happen when execution cannot continue under any circumstances, and in such cases all bets are off whether any cleanup code would actually still work. A hard abort might indeed be the best option.
    - edflsafoiewq 3y ago
      That seems overly pessimistic (or perhaps overly optimistic about code that does not panic). Panics mostly exist to guard code from entering into such unrecoverable states, eg writing past the end of an array.
      - flohofwoe 3y ago
        For me the difference would be: if the write past the array has been detected before it happens (via a range check) it would be a regular error which which can be handled, while a panic would be "oops somebody else has written past the end of the array" (e.g. a hitting a canary check), which should abort immediately because at that point it's no longer guaranteed that any recovery code would even work or just make things worse (e.g. trying to flush data from memory back to disk, but that data might have been corrupted too).
        lifthrasiir 3y ago
        You have a good point and lock poisoning had the same reasoning, but wasn't really popular [1]. (In hindsight the poisoning itself was a great idea but should have been decoupled from locks.) Compared to other languages with similar constructs, Rust panic is probably regarded as less fatal because an incorrect but safe Rust code tends to have a limited reach. Ah, and it should be also noted that some non-fatal signals were also delivered only via panic. The best-known example is a memory allocation failure, which is recoverable in Rust but needed unwinding for a long time. Nowadays you have an unsafe but non-unwinding alternative. [1] https://blog.rust-lang.org/2020/12/11/lock-poisoning-survey.html https://blog.rust-lang.org/2020/12/11/lock-poisoning-survey....
        edflsafoiewq 3y ago
- josephg 3y ago
  > These are still okay, but then `panic = "abort"` shakes a lot of code off by making the final executable unable to print a nice stack trace (even without symbols) and instead immediately traps/abort()-s. I just tried this. The stack traces on panic seem more or less the same with or without panic = "abort" in Cargo.toml. For example, this program: fn main() { let v = vec![1, 2, 3]; v[99]; } Compiled with panic="abort" outputs this stack trace: $ RUST_BACKTRACE=1 cargo run --release Compiling rust-panic v0.1.0 (/Users/seph/temp/rust-panic) Finished release [optimized] target(s) in 1.82s Running `target/release/rust-panic` thread 'main' panicked at src/main.rs:4:6: index out of bounds: the len is 3 but the index is 99 stack backtrace: 0: _rust_begin_unwind 1: core::panicking::panic_fmt 2: core::panicking::panic_bounds_check 3: <alloc::vec::Vec<T,A> as core::ops::index::Index<I>>::index 4: rust_panic::main note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace. [1] 95405 abort RUST_BACKTRACE=1 cargo run --release Weirdly, in this test if I don't strip the binary, I get a larger binary size with panic="abort" than when I leave that out. That is surely due to a bug somewhere.
  - ponkpanda 3y ago
    You're not adding the +nightly switch and the required flags to compiled std. Just setting panic=abort in cargo.toml isn't enough. One can get binaries pretty damn small (low-mid tens of kilobytes for a basic cli program doing something like hashing of a file). Problem I've found with manually compiling std (which has ancillary benefits of being able to compile to a specific uarch) is it can break the compilation process when bringing in third-party deps. The config.toml (stored in $PROJECT_ROOT/.cargo) overrides cargo's behaviour for all dependencies as well - which may break those compilations. Tbh, it's one reason I don't particularly rate the rustc+cargo toolchain - but for most people writing regular applications: just being able to do ```cargo build -r``` and not care about binary size, uarch optimization or custom llvm/rustc optimizations (PGO etc), most won't care.
- lifthrasiir 3y ago
  > `panic = "abort"` shakes a lot of code off by making the final executable unable to print a nice stack trace (even without symbols) and instead immediately traps/abort()-s. I believe it does print backtraces then terminate, since the backtrace is printed via panic hooks, which happen before the actual unwinding.
  - vacuity 3y ago
    Is the backtrace performed by the OS and that's why it still works? And the debug info needs to still be provided, just not an unwinding mechanism?
chrismorgan 3y ago
opt-level z would not be a reasonable default: you should normally optimise for speed, not binary size. lto and codegen-units=1 have a huge compile time cost. For release for general distribution you should tend to favour them, but the release profile isn’t just about that activity (especially because debug/opt-level<2 is often just too slow to use while developing). You commonly want to create another profile for production distribution. Abort on panic changes runtime behaviour by stopping you from catching panics, which will completely break some programs, and harm the failure mode of others, so that e.g. one defective route on a web server will suddenly take the entire website down for everyone (or, if you have a supervisor that can restart the server, at least disrupt it for everyone).
- flohofwoe 3y ago
  > you should normally optimise for speed, not binary size IME optimize for speed vs size usually isn't as clear cut as the name says though, sometimes smaller code does indeed run faster, but in most cases I've seen there's not much of a difference between -O3, -O2, -Os and -Oz.
  - kibwen 3y ago
    Weirdly, most of the time I find that -O3 produces smaller binaries than -Oz.
lifthrasiir 3y ago
Comparing with the current Cargo default [1]: • `panic = "abort"` means that any panic terminates the program. This is not always desirable because you may want to catch and recover from panics, particularly in long-running servers. • `strip = true` means that anything depending on DWARF would no longer work. Backtraces won't work, but also unwinding will no longer work (so this is disastrous if you haven't set `panic` above). The actual proposal has `strip = "debuginfo"` instead, so unwinding will work while backtraces won't. • `codegen-units = 1` is the number of concurrent compilation jobs (cgu) in the LLVM codegen phase. A single cgu will significantly increase the compilation time, while allowing a bit more optimization. Otherwise this is okay. • `lto = true` enables Rust-specific link-time optimizations across crates. The actual benefit depends on the set of crates linked, but it is significantly slower that many large enough projects wouldn't want it. It does benefit small programs like the "Hello, world" program the most though. • `opt-level = "z"` is same to C/C++ `-Oz` and the same pros and cons apply. [1] https://doc.rust-lang.org/cargo/reference/profiles.html#release https://doc.rust-lang.org/cargo/reference/profiles.html#rele...
- flohofwoe 3y ago
  All makes sense, but I don't agree with: > This is not always desirable because you may want to catch and recover from panics, particularly in long-running servers. IMHO a panic implies that execution cannot continue under any circumstances, and even any attempts for a graceful shutdown might be futile (if recovery is possible it shouldn't be a panic but done through regular error handling). For a server process the best reaction to a panic would mean abort and clean restart. > A single cgu will significantly increase the compilation time, while allowing a bit more optimization. Increased build time is acceptable for release mode IMHO.
  - robinsonrc 3y ago
    I remember my disappointment when I found out panics could be “caught” and that I was still living in the world of exceptions
    - josephg 3y ago