support AT_SYSINFO and AT_SYSINFO_EHDR on all architectures

[pattop]

Not sure why AT_SYSINFO and AT_SYSINFO_EHDR were limited to x86 and x86/x86_64 respectively.

Linux sets AT_SYSINFO on ia64 and x86 and AT_SYSINFO_EHDR on all architectures.

Removing the the architecture guard on AT_SYSINFO is harmless as the identifier (32) is not reused on other architectures, so the code will work correctly without an architecture guard.

[rjzak]

Would this inhibit using the crate on Linux for other platforms, like arm?

[npmccallum]

@pattop @rjzak See the documentation here: https://man7.org/linux/man-pages/man3/getauxval.3.html

[pattop]

Would this inhibit using the crate on Linux for other platforms, like arm?

No, this fixes the crate on other platforms. It's currently broken on everything other than x86 and x86_64.

[pattop]

@pattop @rjzak See the documentation here: https://man7.org/linux/man-pages/man3/getauxval.3.html

That's a very good point. I raised this to fix https://github.com/enarx/vdso on arm64. But in hindsight the vdso crate really should be using the libc function.

This is broken in other ways too. You can't rely on the environ pointer as a way to access auxv as setting any environment variable in the process will change environ to point somewhere else leading to undefined behaviour in from_environ() as it walks off the end of the array.