The SSL certificate is invalid on sparc64 when cargo is fetching the index

Problem

It appears that there might be some bug in how cargo does its certificate validation on sparc64. It possibly may extend to other big-endian systems as well, but I haven’t been able to verify it (on both mips64 and ppc64 things I have access to the glibc is too old for rustup).

$ cargo update
    Updating crates.io index
error: failed to load source for a dependency on `cc`                                                                                                                                                                                          

Caused by:
  Unable to update registry `https://github.com/rust-lang/crates.io-index`

Caused by:
  failed to fetch `https://github.com/rust-lang/crates.io-index`

Caused by:
  the SSL certificate is invalid: 0x08 - The certificate is not correctly signed by the trusted CA; class=Ssl (16); code=Certificate (-17)
$ git clone https://github.com/rust-lang/crates.io-index
Cloning into 'crates.io-index'...
remote: Enumerating objects: 247, done.
remote: Counting objects: 100% (247/247), done.
remote: Compressing objects: 100% (233/233), done.
remote: Total 627507 (delta 123), reused 124 (delta 0), pack-reused 627260
Receiving objects: 100% (627507/627507), 128.29 MiB | 7.89 MiB/s, done.
Resolving deltas: 100% (412075/412075), done.
Checking out files: 100% (21150/21150), done.
$ curl 'https://crates.io/'
{"errors":[{"detail":"Not Found"}]}

Steps

1. On a SPARC64-based machine update the cargo index (by trying to build a rust library for the first time)

Possible Solution(s)

1. Figure out and fix the SSL issues;
2. Provide some way to disable certificate checking temporarily;
3. Make it easy to check-out the index manually...

Notes

$ cargo version
cargo 1.30.0
$ uname -a
Linux gcc202 4.19.0-rc7-sparc64-smp #1 SMP Debian 4.19~rc7-1~exp1 (2018-10-07) sparc64 GNU/Linux
$ ldd $(which cargo)
	linux-vdso.so.1 (0xfff800010002e000)
	libgit2.so.27 => /usr/lib/sparc64-linux-gnu/libgit2.so.27 (0xfff8000100c18000)
	libssh2.so.1 => /usr/lib/sparc64-linux-gnu/libssh2.so.1 (0xfff8000100dec000)
	libcurl-gnutls.so.4 => /usr/lib/sparc64-linux-gnu/libcurl-gnutls.so.4 (0xfff8000100f18000)
	libssl.so.1.1 => /usr/lib/sparc64-linux-gnu/libssl.so.1.1 (0xfff8000101098000)
	libcrypto.so.1.1 => /usr/lib/sparc64-linux-gnu/libcrypto.so.1.1 (0xfff8000101224000)
	libz.so.1 => /lib/sparc64-linux-gnu/libz.so.1 (0xfff80001015b8000)
	libdl.so.2 => /lib/sparc64-linux-gnu/libdl.so.2 (0xfff80001016d8000)
	librt.so.1 => /lib/sparc64-linux-gnu/librt.so.1 (0xfff80001017e0000)
	libpthread.so.0 => /lib/sparc64-linux-gnu/libpthread.so.0 (0xfff80001018ec000)
	libgcc_s.so.1 => /lib/sparc64-linux-gnu/libgcc_s.so.1 (0xfff8000101a0c000)
	libc.so.6 => /lib/sparc64-linux-gnu/libc.so.6 (0xfff8000101b20000)
	/lib64/ld-linux.so.2 (0xfff8000100000000)
	libm.so.6 => /lib/sparc64-linux-gnu/libm.so.6 (0xfff8000101d8c000)
	libmbedtls.so.12 => /usr/lib/sparc64-linux-gnu/libmbedtls.so.12 (0xfff8000101f70000)
	libmbedx509.so.0 => /usr/lib/sparc64-linux-gnu/libmbedx509.so.0 (0xfff800010209c000)
	libmbedcrypto.so.3 => /usr/lib/sparc64-linux-gnu/libmbedcrypto.so.3 (0xfff80001021b0000)
	libhttp_parser.so.2.8 => /usr/lib/sparc64-linux-gnu/libhttp_parser.so.2.8 (0xfff8000102310000)
	libgssapi_krb5.so.2 => /usr/lib/sparc64-linux-gnu/libgssapi_krb5.so.2 (0xfff800010241c000)
	libkrb5.so.3 => /usr/lib/sparc64-linux-gnu/libkrb5.so.3 (0xfff8000102560000)
	libk5crypto.so.3 => /usr/lib/sparc64-linux-gnu/libk5crypto.so.3 (0xfff800010272c000)
	libcom_err.so.2 => /lib/sparc64-linux-gnu/libcom_err.so.2 (0xfff8000102860000)
	libgcrypt.so.20 => /lib/sparc64-linux-gnu/libgcrypt.so.20 (0xfff8000102968000)
	libnghttp2.so.14 => /usr/lib/sparc64-linux-gnu/libnghttp2.so.14 (0xfff8000102b2c000)
	libidn2.so.0 => /usr/lib/sparc64-linux-gnu/libidn2.so.0 (0xfff8000102c50000)
	librtmp.so.1 => /usr/lib/sparc64-linux-gnu/librtmp.so.1 (0xfff8000102d70000)
	libpsl.so.5 => /usr/lib/sparc64-linux-gnu/libpsl.so.5 (0xfff8000102e8c000)
	libnettle.so.6 => /usr/lib/sparc64-linux-gnu/libnettle.so.6 (0xfff8000102fa0000)
	libgnutls.so.30 => /usr/lib/sparc64-linux-gnu/libgnutls.so.30 (0xfff80001030dc000)
	libldap_r-2.4.so.2 => /usr/lib/sparc64-linux-gnu/libldap_r-2.4.so.2 (0xfff8000103330000)
	liblber-2.4.so.2 => /usr/lib/sparc64-linux-gnu/liblber-2.4.so.2 (0xfff8000103480000)
	libmbedcrypto.so.1 => /usr/lib/sparc64-linux-gnu/libmbedcrypto.so.1 (0xfff8000103590000)
	libkrb5support.so.0 => /usr/lib/sparc64-linux-gnu/libkrb5support.so.0 (0xfff80001036f0000)
	libkeyutils.so.1 => /lib/sparc64-linux-gnu/libkeyutils.so.1 (0xfff80001037fc000)
	libresolv.so.2 => /lib/sparc64-linux-gnu/libresolv.so.2 (0xfff8000103904000)
	libgpg-error.so.0 => /lib/sparc64-linux-gnu/libgpg-error.so.0 (0xfff8000103a1c000)
	libunistring.so.2 => /usr/lib/sparc64-linux-gnu/libunistring.so.2 (0xfff8000103b3c000)
	libhogweed.so.4 => /usr/lib/sparc64-linux-gnu/libhogweed.so.4 (0xfff8000103dbc000)
	libgmp.so.10 => /usr/lib/sparc64-linux-gnu/libgmp.so.10 (0xfff8000103ef0000)
	libp11-kit.so.0 => /usr/lib/sparc64-linux-gnu/libp11-kit.so.0 (0xfff8000104068000)
	libtasn1.so.6 => /usr/lib/sparc64-linux-gnu/libtasn1.so.6 (0xfff8000104284000)
	libsasl2.so.2 => /usr/lib/sparc64-linux-gnu/libsasl2.so.2 (0xfff8000104398000)
	libffi.so.6 => /usr/lib/sparc64-linux-gnu/libffi.so.6 (0xfff80001044b4000)

Start by reproducing the failure with cargo update or the first cargo build on a SPARC64 system, then trace the crates.io index fetch and certificate-validation path used by Cargo 1.30.0 and its listed SSL/Git dependencies. Done means the index fetch succeeds with normal certificate checking on SPARC64, or the issue is narrowed to a documented dependency or platform limitation; no source file or test is identified in the report.