SegFault when linking against shared libraries on Alpine

help
1

Hi!

Recently I've encountered a problem of rustc on Alpine: linking against any share libraries works fine but results in a binary which generate SegFault errors all the time? Could I get some help here?

Below is a simple and reproducible example, tested on Alpine 3.18:

main.rs:

use std::os::raw::c_int;
#[link(name = "test")]
extern "C" {
    fn testtt() -> c_int;
}
fn main() {
    unsafe { testtt() };
}

test.c:

int testtt() {
  return 32;
}

Generate libtest shared library:

gcc test.c -shared -o libtest.so -fPIC

Compile:

LIBRARY_PATH=.  rustc  -g main.rs

Check and run:

$ LD_LIBRARY_PATH=. ldd ./main
	/lib/ld-musl-x86_64.so.1 (0x7fe41d1f4000)
	libtest.so => ./libtest.so (0x7fe41d186000)

$ LD_LIBRARY_PATH=.  ./main
Segmentation fault
2

did you run the program under gdb? the debugger should be able to catch the signal and show the actual offending instruction location and the call stack.

3

Yes, the instruction causing SegFault is the one loading/calling dynamic symbol testtt, and backtrace has little useful information:

(gdb) backtrace
#0  0x0000000000000000 in ?? ()
#1  0x00007ffff7f9d657 in main::main () at main.rs:17
4

Works fine.

LD_LIBRARY_PATH=. ldd ./main
        /lib/ld-musl-x86_64.so.1 (0x7f4d49615000)
        libtest.so => ./libtest.so (0x7f4d495bf000)
        libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x7f4d495a1000)
        libc.musl-x86_64.so.1 => /lib/ld-musl-x86_64.so.1 (0x7f4d49615000)

Did you install rust (& gcc) using apk?

5

Can you try

use std::os::raw::c_int;
extern "C" {
    fn testtt() -> c_int;
}
fn main() {
    unsafe { testtt() };
}

and

LIBRARY_PATH=.  rustc  -g main.rs -ltest
6

Interesting difference between your ldd output and that of OP is that you link musl libc dynamically. Maybe that makes a difference?

7

Did you install rust (& gcc) using apk?

No, apk doesn't offer rust or cargo. AFAIK installing rust on apline by rustup is the only way to use it.

Works fine.

May I have your configuration: the stable or nightly channel? and the compiler options? and OS version?

8

Problem solved, by adding -C target-feature=-crt-static flag to rustc.

ref: Tracking issue for musl host toolchain · Issue #59302 · rust-lang/rust · GitHub

9

the alpine community repository does have rust available. there's only stable rust though, nightly is unavailable.

oh, that explains why @jonh and I didn't encounter the crash. the crt-static feature is turned off by default by the apk community package maintainer. see this patch:

https://git.alpinelinux.org/aports/tree/community/rust/musl-fix-linux_musl_base.patch?h=3.18-stable#n23

10

It is helpful information, thanks for pointing out that!