Linux armv7 support

[orobio]

On linux/armv7 some symbols are not properly prefixed. Building a project that includes both swift-nio-ssl and swift-crypto, results in the following conflicts:

ld.lld: error: duplicate symbol: CRYPTO_poly1305_init_neon
ld.lld: error: duplicate symbol: CRYPTO_poly1305_update_neon
ld.lld: error: duplicate symbol: CRYPTO_poly1305_finish_neon
ld.lld: error: duplicate symbol: openssl_poly1305_neon2_blocks
ld.lld: error: duplicate symbol: openssl_poly1305_neon2_addmulmod
ld.lld: error: duplicate symbol: vpaes_encrypt_key_to_bsaes
ld.lld: error: duplicate symbol: vpaes_decrypt_key_to_bsaes
ld.lld: error: duplicate symbol: sha512_block_data_order_neon
ld.lld: error: duplicate symbol: sha256_block_data_order_neon
ld.lld: error: duplicate symbol: bsaes_cbc_encrypt
ld.lld: error: duplicate symbol: bsaes_ctr32_encrypt_blocks
ld.lld: error: duplicate symbol: x25519_NEON
ld.lld: error: duplicate symbol: CRYPTO_has_broken_NEON
ld.lld: error: duplicate symbol: CRYPTO_needs_hwcap2_workaround

It looks like CCryptoBoringSSL_boringssl_prefix_symbols.h is generated by vendor-boringssl.sh by building BoringSSL for various architectures and gathering all symbols. There is no official linux/armv7 docker image yet, so at the moment we can't use the same method for adding these symbols, but would it be possible to create a temporary solution, for example by hardcoding these symbols? Or is there any proper solution that could work without requiring an official linux/armv7 docker?

[Lukasa]

I'd be open to an unofficial docker image, but I don't think hardcoding the symbols themselves is going to work. Another option might be to produce a cross-compilation SDK that supports an armv7 toolchain, which we could then integrate. @MaxDesiatov might be able to help with that.

[MaxDesiatov]

Swift SDKs can be generated from existing toolchains. Thus we need an armv7 toolchain first (for some Linux distribution, Docker images could work too) to run the generator on it.

[orobio]

We don't have a full toolchain for armv7, but we do have a cross-compiling toolchain (Swift 5.10). This was created with something based on the swift-armv7 repo. However, it is for our own Yocto based system. We can have a look at creating a container image with a cross-compiling toolchain for Debian. This should be usable with the vendor-boringssl.sh script. I guess it will not work well with the SDK generator, though.

[Lukasa]

Ideally we'd have either a suitable docker container or a toolchain, I don't much mind. Either way we can add that to the build system once we're there.

[orobio]

A container seems like the best option for now. It fits right into the current set-up and takes away some unknowns regarding SDK creation, especially for us being unfamiliar with Swift on MacOS. I submitted a pull request with a container based solution.