Link error with v0.11.0 rust-lld: error: undefined symbol: mbedtls_pk_ec__extern mbedtls_cipher_get_cipher_mode__extern

[xiaoyuxlu]

Hi,

I'm trying rust-mbedtls in no_std environment. This problem also exists in std environment with the following code.

    use mbedtls::pk::Pk;
    use mbedtls::pk::{EcGroup, EcGroupId};
    use mbedtls::rng::OsEntropy;
    use mbedtls::rng::CtrDrbg;
    let mut rng = CtrDrbg::new(Arc::new(OsEntropy::new()), None).unwrap();
    let secp256r1 = EcGroup::new(EcGroupId::SecP256R1).unwrap();
    let pk = Pk::generate_ec(&mut rng, secp256r1.clone()).unwrap();
    let peer_key = pk.ec_public().ok().unwrap().to_binary(&secp256r1, false).unwrap();

version 0.9.1 works fine. But the new version 0.11.0 has the following problem.

note: rust-lld: error: undefined symbol: mbedtls_pk_ec__extern
           ...
          >>> referenced 2 more times
          
          rust-lld: error: undefined symbol: mbedtls_cipher_get_cipher_mode__extern
          ...
         >>> referenced 1 more times

Investigate:

objdump -D -S target/release/build/mbedtls-sys-auto-694c12a76746dc19/out/libstatic-wrappers.a | grep mbedtls_pk_ec
Disassembly of section .gnu.lto_mbedtls_pk_ec__extern.c11f27ebb7176389:
0000000000000000 <.gnu.lto_mbedtls_pk_ec__extern.c11f27ebb7176389>:

Is it the reason of .gnu.lto?

Comment out this line. This problem is gone.

rust-mbedtls/mbedtls-sys/build/build.rs

Line 144 in c274ee9

.flag_if_supported("-flto=thin")

Can disable this optimization option?

@Taowyoo any comments?

[Taowyoo]

It seems LTO does not works good with all compiler and linkers.
Could you create a PR for removing this?

[xiaoyuxlu]

It seems LTO does not works good with all compiler and linkers. Could you create a PR for removing this?

Done. Please take a look #305. Thank you.