Tests fail with latest rustc.

[plugwash]

Related to #232

The "validate" function tries to write data to a pipe from a pointer of unknown validity.

Unfortunately, the function tries to convert the possibly-invalid pointer to a slice, this is unsound and with recent rustc leads to the testsuite panicing

thread 'addr_validate::test::failed_validate' panicked at library/core/src/panicking.rs:220:5:
unsafe precondition(s) violated: slice::from_raw_parts requires the pointer to be aligned and non-null, and the total size of the slice not to exceed `isize::MAX`

In Debian I fixed this by using libc::write directly instead of nix::unistd::write

https://salsa.debian.org/rust-team/debcargo-conf/-/blob/master/src/pprof/debian/patches/use-libc-write-for-validation.patch

[shinmao]

@plugwash , do you have any other case that could trigger the panic on validate? As far as I know, even though the test suite panic; however, no one will use it like this way (pass a constant address), isn't it?

pprof-rs/src/addr_validate.rs

Line 126 in 4939f73

assert!(!validate(-1_i32 as usize as *const libc::c_void))

[plugwash]

No, I simply ran into the test failure while working on Debian rust packaging.

[shinmao]

Yes. I think validate(-1_i32 as usize as *const libc::c_void) is expected to return false here; however, it panic due to precondition check in from_raw_parts.