CMSG_NXTHDR hits a Bus Error on sparc64-unknown-linux-gnu

[asomers]

PR #1235 adds a new test program to ensure that the cmsg(3) family of functions are correctly implemented on all targets. However, when run in QEMU CMSG_NXTHDR hits a Bus Error. This could be an error in libc's CMSG_NXTHDR implementation for that platform, or it could be an error in Linux's definition of the macro (doesn't work on unaligned buffers or something like that). Less likely would be an error in QEMU. Lacking access to sparc hardware, I didn't investigate further.

https://travis-ci.com/rust-lang/libc/jobs/175199673

[gnzlbg]

This reproduces on master, that is, updating the Debian version did not fix this (it did fix the s390x issue).

Chances are, there is a bug in our implementation.

[gnzlbg]

I'm also seeing sometimes a:

running 5 tests
test t::test_cmsg_data ... ok
error: process didn't exit successfully: `qemu-arm -L /musl-arm /checkout/target/arm-unknown-linux-musleabihf/debug/deps/cmsg-7238071f2e3df703` (signal: 11, SIGSEGV: invalid memory reference)
The command "if [[ $TRAVIS_OS_NAME = "linux" ]] && [[ $BUILD_ONLY != "1" ]]; then sh ci/run-docker.sh $TARGET; else sh ci/run.sh $TARGET; fi" exited with 101.

seg fault on the arm build jobs in the cmsg tests. Restarting the build job fixes the issue, but it might mean that something fishy is going on there.