Currently the standard library has some pretty complicated logic to detect
whether #[thread_local] should be used or whether it's supported. This is also
unfortunately not quite true for OSX where not all versions support
the #[thread_local] attribute (only 10.7+ does). Compiling code for OSX 10.6 is
typically requested via the MACOSX_DEPLOYMENT_TARGET environment variable (e.g.
the linker recognizes this), but the standard library unfortunately does not
respect this.
This commit updates the compiler to add a `target_thread_local` cfg annotation
if the platform being targeted supports the `#[thread_local]` attribute. This is
feature gated for now, and it is only true on non-aarch64 Linux and 10.7+ OSX
(e.g. what the module already does today). Logic has also been added to parse
the deployment target environment variable.
Note: for now, this change only affects `-windows-gnu` builds.
So why was this `libgcc` dylib dependency needed in the first place?
The stack unwinder needs to know about locations of unwind tables of all the modules loaded in the current process. The easiest portable way of achieving this is to have each module register itself with the unwinder when loaded into the process. All modules compiled by GCC do this by calling the __register_frame_info() in their startup code (that's `crtbegin.o` and `crtend.o`, which are automatically linked into any gcc output).
Another important piece is that there should be only one copy of the unwinder (and thus unwind tables registry) in the process. This pretty much means that the unwinder must be in a shared library (unless everything is statically linked).
Now, Rust compiler tries very hard to make sure that any given Rust crate appears in the final output just once. So if we link the unwinder statically to one of Rust's crates, everything should be fine.
Unfortunately, GCC startup objects are built under assumption that `libgcc` is the one true place for the unwind info registry, so I couldn't find any better way than to replace them. So out go `crtbegin`/`crtend`, in come `rsbegin`/`rsend`!
A side benefit of this change is that rustc is now more in control of the command line that goes to the linker, so we could stop using `gcc` as the linker driver and just invoke `ld` directly.
Since it isn't possible to disable linkage of just GCC startup objects, we now need logic for finding libc installation directory and copying the required startup files (e.g. crt2.o) to rustlib directory.
Bonus change: use the `-nodefaultlibs` flag on Windows, thus paving the way to direct linker invocation.
This commit updates the compiler to not attempt to use jemalloc for platforms
where jemalloc is never enabled. Currently the compiler attempts to link in
jemalloc based on whether `--disable-jemalloc` was specified at build time for
the compiler itself, but this is only the right decision for the host target,
not for other targets.
This still leaves a hole open where a set of target libraries are downloaded
which were built with `--disable-jemalloc` and the compiler is unaware of that,
but this is a pretty rare case so it can always be fixed later.
For most parts, rumprun currently looks like NetBSD, as they share the same
libc and drivers. However, being a unikernel, rumprun does not support
process management, signals or virtual memory, so related functions
might fail at runtime. Stack guards are disabled exactly for this reason.
Code for rumprun is always cross-compiled, it uses always static
linking and needs a custom linker.
This commit updates the compiler to not attempt to use jemalloc for platforms
where jemalloc is never enabled. Currently the compiler attempts to link in
jemalloc based on whether `--disable-jemalloc` was specified at build time for
the compiler itself, but this is only the right decision for the host target,
not for other targets.
This still leaves a hole open where a set of target libraries are downloaded
which were built with `--disable-jemalloc` and the compiler is unaware of that,
but this is a pretty rare case so it can always be fixed later.
This adds a new target property, `target_vendor` which can be used as a
matcher for conditional compilation. The vendor is part of the autoconf
target triple: <arch><sub>-<vendor>-<os>-<env>
The default value for `target_vendor` is "unknown".
Matching against the `target_vendor` with `#[cfg]` is currently feature
gated as `cfg_target_vendor`.
If set to false, `-nodefaultlibs` is not passed to the linker. This
was the default behavior on Windows, but it should be configurable
per target.
This is a [breaking-change] for target specifications that have
the `is_like_windows` option set to true. Such targets need to
set `no_default_libraries` to false in order to restore the old
behavior.
- All the libstd tests are passing in the optimized build against
a Zenfone2 and the x86 Android emulator.
I haven't tested the other libraries though.
This commit is an implementation of [RFC 1183][rfc] which allows swapping out
the default allocator on nightly Rust. No new stable surface area should be
added as a part of this commit.
[rfc]: https://github.com/rust-lang/rfcs/pull/1183
Two new attributes have been added to the compiler:
* `#![needs_allocator]` - this is used by liballoc (and likely only liballoc) to
indicate that it requires an allocator crate to be in scope.
* `#![allocator]` - this is a indicator that the crate is an allocator which can
satisfy the `needs_allocator` attribute above.
The ABI of the allocator crate is defined to be a set of symbols that implement
the standard Rust allocation/deallocation functions. The symbols are not
currently checked for exhaustiveness or typechecked. There are also a number of
restrictions on these crates:
* An allocator crate cannot transitively depend on a crate that is flagged as
needing an allocator (e.g. allocator crates can't depend on liballoc).
* There can only be one explicitly linked allocator in a final image.
* If no allocator is explicitly requested one will be injected on behalf of the
compiler. Binaries and Rust dylibs will use jemalloc by default where
available and staticlibs/other dylibs will use the system allocator by
default.
Two allocators are provided by the distribution by default, `alloc_system` and
`alloc_jemalloc` which operate as advertised.
Closes#27389
This commit leverages the runtime support for DWARF exception info added
in #27210 to enable unwinding by default on 64-bit MSVC. This also additionally
adds a few minor fixes here and there in the test harness and such to get
`make check` entirely passing on 64-bit MSVC:
* The invocation of `maketest.py` now works with spaces/quotes in CC
* debuginfo tests are disabled on MSVC
* A link error for librustc was hacked around (see #27438)
This commit leverages the runtime support for DWARF exception info added
in #27210 to enable unwinding by default on 64-bit MSVC. This also additionally
adds a few minor fixes here and there in the test harness and such to get
`make check` entirely passing on 64-bit MSVC:
* The invocation of `maketest.py` now works with spaces/quotes in CC
* debuginfo tests are disabled on MSVC
* A link error for librustc was hacked around (see #27438)
This means that we no longer need to ship the `llvm-ar.exe` binary in the MSVC
distribution, and after a snapshot we can remove a good bit of logic from the
makefiles!
This means that we no longer need to ship the `llvm-ar.exe` binary in the MSVC
distribution, and after a snapshot we can remove a good bit of logic from the
makefiles!
This commit removes all morestack support from the compiler which entails:
* Segmented stacks are no longer emitted in codegen.
* We no longer build or distribute libmorestack.a
* The `stack_exhausted` lang item is no longer required
The only current use of the segmented stack support in LLVM is to detect stack
overflow. This is no longer really required, however, because we already have
guard pages for all threads and registered signal handlers watching for a
segfault on those pages (to print out a stack overflow message). Additionally,
major platforms (aka Windows) already don't use morestack.
This means that Rust is by default less likely to catch stack overflows because
if a function takes up more than one page of stack space it won't hit the guard
page. This is what the purpose of morestack was (to catch this case), but it's
better served with stack probes which have more cross platform support and no
runtime support necessary. Until LLVM supports this for all platform it looks
like morestack isn't really buying us much.
cc #16012 (still need stack probes)
Closes#26458 (a drive-by fix to help diagnostics on stack overflow)
