Add --enable-debug flag to musl CI build script

[alecmocatta]

Building for x86_64-unknown-linux-musl currently results in an executable lacking debug information for musl libc itself. If you request a backtrace in GDB while control flow is within musl – including sycalls made by musl – the result looks like:

#0  0x0000000000434b46 in __cp_end ()
#1  0x0000000000432dbd in __syscall_cp_c ()
#2  0x0000000000000000 in ?? ()

i.e. not very helpful. Adding --enable-debug resolves this, and --enable-optimize re-enables optimisations which default to off given the previous flag.

[pietroalbini]

Thanks for this PR! The triage team will periodically check in to make sure this PR is reviewed.

r? @alexcrichton

[alexcrichton]

Thanks for this! To confirm, you've tested the resulting binaries and they're optimized correctly and have debug information?

Also are there other settings that this implies? I'd just wanna make sure that things like malloc and memcpy don't tank in performance by accident

[alecmocatta]

Yes I have indeed been running the resulting binaries, and they do indeed have debug info and are optimised:

(gdb) bt
#0  __syscall () at src/internal/x86_64/syscall.s:13
#1  0x000000000045e3f8 in nanosleep (req=<optimized out>, rem=<optimized out>) at src/time/nanosleep.c:7
#2  0x0000000000445833 in std::sys::unix::thread::Thread::sleep::h5a6a14352632043c ()
#3  0x000000000040032b in x::main::h33e0397ddc129856 ()
#4  0x0000000000400403 in std::rt::lang_start::_$u7b$$u7b$closure$u7d$$u7d$::h7e9e7f9d5763a160 ()
#5  0x000000000043f6f3 in std::panicking::try::do_call::h652c91b274df4c69 ()
#6  0x000000000045017a in __rust_maybe_catch_panic ()
#7  0x000000000043e5d7 in std::rt::lang_start_internal::h2e87c2c21b125ac0 ()
#8  0x00000000004003e7 in std::rt::lang_start::h57093f2887229336 ()
#9  0x000000000040034e in main ()

[alecmocatta]

I also just sanity checked memcpy performance against apt-installed x86_64-unknown-linux-gnu, and it is indeed comparable:

$ rustc --target x86_64-unknown-linux-gnu -C opt-level=3 ./x.rs && ./x
Duration { secs: 2, nanos: 8780924 }

$ rustc --target x86_64-unknown-linux-musl -C opt-level=3 ./x.rs && ./x
Duration { secs: 2, nanos: 364127222 }

fn main() {
	let mut x: Vec<u8> = Vec::with_capacity(1_000_000_000);
	let mut y: Vec<u8> = Vec::with_capacity(x.capacity()); unsafe{y.set_len(x.capacity())};
	let time = std::time::Instant::now();
	for i in 0..x.capacity() {
		x.push(i as u8);
	}
	unsafe{memcpy(&mut x[0], &y[0], x.capacity())};
	println!("{:?}", time.elapsed());
}

[alexcrichton]

@bors: r+

Ok great, thanks for verifying!

[bors]

📌 Commit 18e9532 has been approved by alexcrichton