Add atomic support for pre-ARMv6 on Linux
This uses the [kernel user helpers](https://www.kernel.org/doc/Documentation/arm/kernel_user_helpers.txt) which are available starting from kernel 2.6.15. Since Rust currently requires 2.6.18 at a minimum, this should be fine in practice. I did not include support for 64-bit atomics since that functionality is only available in kernel 3.1.
This PR allows Rust to work on older ARM versions such as ARMv4 and ARMv5 with the full libstd.
Implement x86 chkstk in "rust"
cc #183
Basically the same as the x86_64 ones, except `__alloca` doesn't need to fix the parameter register. I've manually verified that the disassembly is the same, and that these work in a compiled rust program.
The second commit disables compiling probestack functions for `feature = mangled-names`. They aren't needed during testing because they aren't comparison tested and the unmangled versions are the ones that actually get used.
r? @alexcrichton
Update rustbuild commentary
r? @nikomatsakis
This is the reason that https://github.com/rust-lang/rust/pull/44509 doesn't work - the `rustbuild` feature _is_ actually used, it was just incorrectly documented here and I missed it.
Update the gcc crate to 0.3.53 and disable compilation warnings
The update is needed because you'd otherwise get a deprecation warning about `Config` being deprecated, as rust-lang/rust has updated the gcc crate.
The compilation warnings are inside the compiler-rt submodule, about which we don't have
direct control over, so we disable them.
Tweak definition of probestack functions
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.
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.
Use the Rust implementation of udivsi3 on ARM
Although compiler-rt presumably has a more optimized implementation written in
assembly, it appears buggy for whatever reason, causing #173.
For now let's see if integration into rust-lang/rust will work with the
Rust-defined implementation!
