Allow asserts and panics to abort process quietly.

[vi]

Currently assertions cause executable to be bloated up by various formatting-related symbols like

 0.5%   2.8%   1020B       std <core::fmt::builders::PadAdapter<'_> as core::fmt::Write>::write_str
 0.4%   2.3%    860B       std core::char::methods::<impl char>::escape_debug
 0.4%   2.2%    804B       std core::fmt::Formatter::pad_integral

, causing executables that carefully choose functions to call in order to stay under X kilobytes to suddenly grow by about 40-150 kilobytes. Additionally, pthread_* symbols appear in otherwise single-threaded module. Symbol count may jump by about 800.

Shall there be some mode (like panic = "really-abort") or a libstd feature settable in Xargo.toml that makes all panics just do plain raw abort without trying to collect backtrace or print anything at all?

[vi]

Looks like making panicking::{continue_panic_fmt,begin_panic} just do the abort makes it small again.

Is a pull request about this welcome?

[vi]

With the new feature merged in, one can opt out formatting and panic handling using panic_immediate_abort and #![no_main]. This can bring static executable size under 20 kilobytes.

You need to

• use Xargo,
• #![no_main] #[no_mangle] pub fn main(...) {...},
• std = {default-features=false, features=["panic_immediate_abort"]} line in Xargo.toml,
• panic=abort,
• LTO,
• and obviously avoid println! or format! yourself (including in libs).

All panics and failed asserts will just cause Illegal Instruction.

[rhendric]

Hey @vi, I'm so glad you got this in! I followed your instructions above and my binaries are getting smaller. However, ldd tells me that there's still a libpthread dependency in my compiled (single-threaded) binaries. Have you succeeded in getting rid of that?

[vi]

Try the minimal example:

src/main.rs:

#![no_main]

#[no_mangle]
pub fn main() {

}

Xargo.toml:

[dependencies]
std = {default-features=false, features=["panic_immediate_abort"]}

Cargo.toml:

[package]
name = "tiny"
version = "0.1.0"
authors = []
edition = "2018"

[profile.release]
opt-level = "s"
debug = false
rpath = false
lto = true
debug-assertions = false
codegen-units = 1
panic = 'abort'
incremental = false

Commands:

$ xargo build --release --target=x86_64-unknown-linux-gnu
    Updating crates.io index
   Compiling cc v1.0.25
   Compiling build_helper v0.1.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/build_helper)
   Compiling core v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore)
   Compiling unwind v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libunwind)
   Compiling compiler_builtins v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/rustc/compiler_builtins_shim)
   Compiling cmake v0.1.35
   Compiling std v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd)
   Compiling rustc_asan v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/librustc_asan)
   Compiling rustc_tsan v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/librustc_tsan)
   Compiling rustc_msan v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/librustc_msan)
   Compiling rustc_lsan v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/librustc_lsan)
   Compiling libc v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/rustc/libc_shim)
   Compiling alloc v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/liballoc)
   Compiling panic_abort v0.0.0 (/nix/rust/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libpanic_abort)
    Finished release [optimized] target(s) in 1m 01s
   Compiling tiny v0.1.0 (/tmp/rstiny)
    Finished release [optimized] target(s) in 0.52s

$ strip target/x86_64-unknown-linux-gnu/release/tiny -o tiny

$ ldd tiny 
	linux-vdso.so.1 (0x000003fdde54f000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x000003d847699000)
	/lib64/ld-linux-x86-64.so.2 (0x0000031694ddc000)

$ ls -lh tiny 
-rwxrwxr-x 1 vi vi 6.0K Dec 10 00:21 tiny

Is it the same for you?

[rhendric]

You're right, I get the same as you. But trying that helped me figure out that adding the libc crate seems to be what adds the libpthread dependency, so thanks!