Re: Re: sysconf(_SC_ARG_MAX) broken in musl.

[Alexander Monakov <amonakov@ispras.ru>]

On Sun, 14 Aug 2016, Rob Landley wrote:
> What happens if your stack size is smaller than 131072? (Not
> stacksize/4, but stacksize total?) I haven't tried, but a quick glance
> looks like Bad Things. And on nommu systems, that may actually come up.

From reading the kernel source, I'm not sure what happens on nommu, but on mmu,
from what I see, what's left for the program is rlimit, minus argv/env/auxv size,
minus variable amount lost due to stack base randomization. In particular, yes,
if rlimit_stack is below 128K and cumulative argv size is high, execve can fail.

So is the concern that the reported sysconf(_SC_ARG_MAX) value is not useful
when stack limit is low? But to know how many arguments you can pass in this
highly constrained situation, you'd have to get rlimit, subtract environment
size (and not even the current environment size, but the environment you're
passing via execve), subtract the worst-case randomization loss, and finally
subtract the amount of stack the invoked program is going to need.

Alexander