This turns the following backtrace,
```
>> bt
#0 0x0000555555576f73 in __rust_probestack () at /cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.14/src/probestack.rs:55
Backtrace stopped: Cannot access memory at address 0x7fffff7fedf0
```
To this:
```
>>> bt
#0 0x0000555555574e47 in __rust_probestack ()
#1 0x00005555555595ba in test::main ()
#2 0x00005555555594f3 in std::rt::lang_start::{{closure}} ()
#3 0x0000555555561ae3 in std::panicking::try::do_call ()
#4 0x000055555556595a in __rust_maybe_catch_panic ()
#5 0x000055555555af9b in std::rt::lang_start_internal ()
#6 0x00005555555594d5 in std::rt::lang_start ()
#7 0x000055555555977b in main ()
```
Use the "volatile" option and the "memory" clobber on inline asm that does
things like return directly, to reduce the chances of compilers rearranging
the code.
It looks like the old `__rust_probestack` routine is incompatible with newer
linux kernels. My best guess for this is that the kernel's auto-growth logic is
failing to trigger, causing what looks like a legitimate segfault to get
delivered. My best guess for why *that's* happening is that the faulting address
is below `%rsp`, whereas previously all faulting stack addresses were above
`%rsp`. The probestack routine does not modify `%rsp` as it's probing the stack,
and presumably newer kernels are interpreting this as a legitimate violation.
This commit tweaks the probestack routine to instead update `%rsp` incrementally
as probing happens. The ABI of the function, however, requires that `%rsp`
isn't changed as part of the function so it's restored at the end to the
previous value.
jethrogb
Tyler Mandry
Adam Schwalm
Runji Wang
Dan Aloni
Alex Crichton
Masaki Hara
Dan Gohman
Matt Ickstadt