Rollup merge of #146627 - madsmtm:jemalloc-simplify, r=jdonszelmann

Simplify `jemalloc` setup

In the past, `#[used]` had to appear in the top-level crate to have a consistent effect on the linker. This has been fixed a while ago for ELF with the introduction of the `symbols.o` file in rust-lang/rust#95604, and more recently for Mach-O in rust-lang/rust#133832, which means that libraries can now implement the required workarounds themselves. This allows moving these `#[used]` declarations out of our `main.rs`.

Specifically, I have moved them into `tikv-jemalloc-sys` where they belong in tikv/jemallocator#109 and done the same for `mimalloc` in purpleprotocol/mimalloc_rust#146 (in case we want to experiment with switching to that one day).

Test with:
```sh
./x build library src/tools/rustdoc src/tools/clippy --set rust.jemalloc=true

# macOS
lldb -- ./build/host/stage1/bin/rustc -vV
(lldb) b _rjem_je_zone_register
(lldb) run
# Should breakpoint, this means that the allocator was properly linked

# Linux
lldb -- ./build/host/stage1/bin/rustc -vV
(lldb) b malloc
(lldb) run
# Should breakpoint, inspect that the `malloc` symbol comes from the `rustc` binary and not from `libc`
```

try-job: `aarch64-gnu`
try-job: `dist-aarch64-linux`
try-job: `dist-x86_64-musl`
try-job: `dist-x86_64-apple`
try-job: `dist-aarch64-apple`

Author: Zalathar

Cargo.toml

@@ -33,8 +33,8 @@ serde_json = { version = "1.0", optional = true }
 # But only for some targets, it fails for others. Rustc configures this in its CI, but we can't
 # easily use that since we support of-tree builds.
 [target.'cfg(any(target_os = "linux", target_os = "macos"))'.dependencies.tikv-jemalloc-sys]
-version = "0.6.0"
-features = ['unprefixed_malloc_on_supported_platforms']
+version = "0.6.1"
+features = ['override_allocator_on_supported_platforms']
 
 [target.'cfg(unix)'.dependencies]
 libc = "0.2"

src/bin/miri.rs

@@ -20,6 +20,11 @@ extern crate rustc_middle;
 extern crate rustc_session;
 extern crate rustc_span;
 
+/// See docs in https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc/src/main.rs
+/// and https://github.com/rust-lang/rust/pull/146627 for why we need this `use` statement.
+#[cfg(any(target_os = "linux", target_os = "macos"))]
+use tikv_jemalloc_sys as _;
+
 mod log;
 
 use std::env;
@@ -392,48 +397,7 @@ fn parse_range(val: &str) -> Result<Range<u32>, &'static str> {
     Ok(from..to)
 }
 
-#[cfg(any(target_os = "linux", target_os = "macos"))]
-fn jemalloc_magic() {
-    // These magic runes are copied from
-    // <https://github.com/rust-lang/rust/blob/e89bd9428f621545c979c0ec686addc6563a394e/compiler/rustc/src/main.rs#L39>.
-    // See there for further comments.
-    use std::os::raw::{c_int, c_void};
-
-    use tikv_jemalloc_sys as jemalloc_sys;
-
-    #[used]
-    static _F1: unsafe extern "C" fn(usize, usize) -> *mut c_void = jemalloc_sys::calloc;
-    #[used]
-    static _F2: unsafe extern "C" fn(*mut *mut c_void, usize, usize) -> c_int =
-        jemalloc_sys::posix_memalign;
-    #[used]
-    static _F3: unsafe extern "C" fn(usize, usize) -> *mut c_void = jemalloc_sys::aligned_alloc;
-    #[used]
-    static _F4: unsafe extern "C" fn(usize) -> *mut c_void = jemalloc_sys::malloc;
-    #[used]
-    static _F5: unsafe extern "C" fn(*mut c_void, usize) -> *mut c_void = jemalloc_sys::realloc;
-    #[used]
-    static _F6: unsafe extern "C" fn(*mut c_void) = jemalloc_sys::free;
-
-    // On OSX, jemalloc doesn't directly override malloc/free, but instead
-    // registers itself with the allocator's zone APIs in a ctor. However,
-    // the linker doesn't seem to consider ctors as "used" when statically
-    // linking, so we need to explicitly depend on the function.
-    #[cfg(target_os = "macos")]
-    {
-        unsafe extern "C" {
-            fn _rjem_je_zone_register();
-        }
-
-        #[used]
-        static _F7: unsafe extern "C" fn() = _rjem_je_zone_register;
-    }
-}
-
 fn main() {
-    #[cfg(any(target_os = "linux", target_os = "macos"))]
-    jemalloc_magic();
-
     let early_dcx = EarlyDiagCtxt::new(ErrorOutputType::default());
 
     // Snapshot a copy of the environment before `rustc` starts messing with it.