[Toybox] getrandom(2)

[Rob Landley]

On 07/06/2018 03:14 PM, enh wrote:
> i'm not sure getrandom(2) is a good choice for a compile-time probe.
> certainly on Android it's common for your libc to be way ahead of your
> kernel.

Hmmm. I didn't expect that. (libc provides a syscall wrapper for a syscall your
kernel doesn't have. Ok...)

Hmmm... I can't compile time probe for what the syscalls return because cross
compiling (and potentially deploying on a different kernel), and I don't want to
make the fallback code ubiquitous because embedded. Hmmm...

I suppose I could make the fallback code's presence depend on CONFIG_TOYBOX_ANDROID?

> in this specific case, on Android getrandom(2) is very likely
> to return ENOSYS. for the arc4random functions (from BSD) we'll try
> getrandom but fall back to open/read/close. seems like xgetrandom
> might be better off doing that, on the assumption that folks will try
> to use prebuilts on old devices/hosts?

Whereas on glibc I have the exact _opposite_ problem, 'FATAL: kernel too old" in
the library loader or entry code, because glibc checks the kernel version and
refuses to run on one older than it was built on. (I.E. gnu/dammit anything is
insane, part several thousand something.)

Lemme try a fix... ok, how's that?

Rob