1 files changed, 63 insertions, 0 deletions
diff --git a/compiler/rustc/src/main.rs b/compiler/rustc/src/main.rs
new file mode 100644
index 000000000..0de1a7819
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+++ b/compiler/rustc/src/main.rs
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+// A note about jemalloc: rustc uses jemalloc when built for CI and
+// distribution. The obvious way to do this is with the `#[global_allocator]`
+// mechanism. However, for complicated reasons (see
+// https://github.com/rust-lang/rust/pull/81782#issuecomment-784438001 for some
+// details) that mechanism doesn't work here. Also, we must use a consistent
+// allocator across the rustc <-> llvm boundary, and `#[global_allocator]`
+// wouldn't provide that.
+//
+// Instead, we use a lower-level mechanism. rustc is linked with jemalloc in a
+// way such that jemalloc's implementation of `malloc`, `free`, etc., override
+// the libc allocator's implementation. This means that Rust's `System`
+// allocator, which calls `libc::malloc()` et al., is actually calling into
+// jemalloc.
+//
+// A consequence of not using `GlobalAlloc` (and the `tikv-jemallocator` crate
+// provides an impl of that trait, which is called `Jemalloc`) is that we
+// cannot use the sized deallocation APIs (`sdallocx`) that jemalloc provides.
+// It's unclear how much performance is lost because of this.
+//
+// As for the symbol overrides in `main` below: we're pulling in a static copy
+// of jemalloc. We need to actually reference its symbols for it to get linked.
+// The two crates we link to here, `std` and `rustc_driver`, are both dynamic
+// libraries. So we must reference jemalloc symbols one way or another, because
+// this file is the only object code in the rustc executable.
+
+fn main() {
+    // See the comment at the top of this file for an explanation of this.
+    #[cfg(feature = "jemalloc-sys")]
+    {
+        use std::os::raw::{c_int, c_void};
+
+        #[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")]
+        {
+            extern "C" {
+                fn _rjem_je_zone_register();
+            }
+
+            #[used]
+            static _F7: unsafe extern "C" fn() = _rjem_je_zone_register;
+        }
+    }
+
+    rustc_driver::set_sigpipe_handler();
+    rustc_driver::main()
+}