This commit applies a few code size optimizations for the wasm target to
the standard library, namely around panics. We notably know that in most
configurations it's impossible for us to print anything in
wasm32-unknown-unknown so we can skip larger portions of panicking that
are otherwise simply informative. This allows us to get quite a nice
size reduction.
Finally we can also tweak where the allocation happens for the
`Box<Any>` that we panic with. By only allocating once unwinding starts
we can reduce the size of a panicking wasm module from 44k to 350 bytes.
These were showing up in tests and in binaries but are trivially optimize-able
away, so add `#[inline]` attributes so LLVM has an opportunity to optimize them
out.
rustc_driver: get rid of the extra thread
**Do not rollup**
We can alter the stack size afterwards on Unix.
Having a separate thread causes poor debugging experience when interrupting with signals. I have to get the backtrace of the all thread, as the main thread is waiting to join doing nothing else. This patch allows me to just run `bt` to get the desired backtrace.
Reduce scope of unsafe block in sun_path_offset
I reduced the scope of the unsafe block to the `uninitialized` call which is the only actual unsafe bit.
The expected behavior is that the environment's PATH should be used
to find the process. posix_spawn() could be used if we iterated
PATH to search for the binary to execute. For now just skip
posix_spawn() if PATH is modified.
spawn() is expected to return an error if the specified file could not be
executed. FreeBSD's posix_spawn() supports returning ENOENT/ENOEXEC if
the exec() fails, which not all platforms support. This brings a very
significant performance improvement for FreeBSD, involving heavy use of
Command in threads, due to fork() invoking jemalloc fork handlers and
causing lock contention. FreeBSD's posix_spawn() avoids this problem
due to using vfork() internally.
Previously, the `guard::init()` and `guard::current()` functions were
returning a `usize` address representing the top of the stack guard,
respectively for the main thread and for spawned threads. The `SIGSEGV`
handler on `unix` targets checked if a fault was within one page below
that address, if so reporting it as a stack overflow.
Now `unix` targets report a `Range<usize>` representing the guard
memory, so it can cover arbitrary guard sizes. Non-`unix` targets which
always return `None` for guards now do so with `Option<!>`, so they
don't pay any overhead.
For `linux-gnu` in particular, the previous guard upper-bound was
`stackaddr + guardsize`, as the protected memory was *inside* the stack.
This was a glibc bug, and starting from 2.27 they are moving the guard
*past* the end of the stack. However, there's no simple way for us to
know where the guard page actually lies, so now we declare it as the
whole range of `stackaddr ± guardsize`, and any fault therein will be
called a stack overflow. This fixes#47863.
Only link res_init() on GNU/*nix
To workaround a bug in glibc <= 2.26 lookup_host() calls res_init() based on the glibc version detected at runtime. While this avoids calling res_init() on platforms where it's not required we will still end up linking against the symbol.
This causes an issue on macOS where res_init() is implemented in a separate library (libresolv.9.dylib) from the main libc. While this is harmless for standalone programs it becomes a problem if Rust code is statically linked against another program. If the linked program doesn't already specify -lresolv it will cause the link to fail. This is captured in issue #46797
Fix this by hooking in to the glibc workaround in `cvt_gai` and only activating it for the "gnu" environment on Unix This should include all glibc platforms while excluding musl, windows-gnu, macOS, FreeBSD, etc.
This has the side benefit of removing the #[cfg] in sys_common; only unix.rs has code related to the workaround now.
Before this commit:
```shell
> cat main.rs
use std::net::ToSocketAddrs;
#[no_mangle]
pub extern "C" fn resolve_test() -> () {
let addr_list = ("google.com.au", 0).to_socket_addrs().unwrap();
println!("{:?}", addr_list);
}
> rustc --crate-type=staticlib main.rs
> clang libmain.a test.c -o combined
Undefined symbols for architecture x86_64:
"_res_9_init", referenced from:
std::net::lookup_host::h93c17fe9ad38464a in libmain.a(std-826c8d3b356e180c.std0.rcgu.o)
ld: symbol(s) not found for architecture x86_64
clang-5.0: error: linker command failed with exit code 1 (use -v to see invocation)
```
Afterwards:
```shell
> rustc --crate-type=staticlib main.rs
> clang libmain.a test.c -o combined
> ./combined
IntoIter([V4(172.217.25.131:0)])
```
Fixes #46797
