1 files changed, 70 insertions, 0 deletions
diff --git a/third_party/libwebrtc/build/rust/std/remap_alloc.c b/third_party/libwebrtc/build/rust/std/remap_alloc.c
new file mode 100644
index 0000000000..ba3b2b0671
--- /dev/null
+++ b/third_party/libwebrtc/build/rust/std/remap_alloc.c
@@ -0,0 +1,70 @@
+// Copyright 2021 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <stddef.h>
+#include <stdlib.h>
+
+#include "build/rust/std/immediate_crash.h"
+
+// When linking a final binary, rustc has to pick between either:
+// * The default Rust allocator
+// * Any #[global_allocator] defined in *any rlib in its dependency tree*
+//   (https://doc.rust-lang.org/edition-guide/rust-2018/platform-and-target-support/global-allocators.html)
+//
+// In this latter case, this fact will be recorded in some of the metadata
+// within the .rlib file. (An .rlib file is just a .a file, but does have
+// additional metadata for use by rustc. This is, as far as I know, the only
+// such metadata we would ideally care about.)
+//
+// In all the linked rlibs,
+// * If 0 crates define a #[global_allocator], rustc uses its default allocator
+// * If 1 crate defines a #[global_allocator], rustc uses that
+// * If >1 crates define a #[global_allocator], rustc bombs out.
+//
+// Because rustc does these checks, it doesn't just have the __rust_alloc
+// symbols defined anywhere (neither in the stdlib nor in any of these
+// crates which have a #[global_allocator] defined.)
+//
+// Instead:
+// Rust's final linking stage invokes dynamic LLVM codegen to create symbols
+// for the basic heap allocation operations. It literally creates a
+// __rust_alloc symbol at link time. Unless any crate has specified a
+// #[global_allocator], it simply calls from __rust_alloc into
+// __rdl_alloc, which is the default Rust allocator. The same applies to a
+// few other symbols.
+//
+// We're not (always) using rustc for final linking. For cases where we're not
+// Rustc as the final linker, we'll define those symbols here instead.
+//
+// In future, we may wish to do something different from using the Rust
+// default allocator (e.g. explicitly redirect to PartitionAlloc). We could
+// do that here, or we could build a crate with a #[global_allocator] and
+// redirect these symbols to that crate instead. The advantage of the latter
+// is that it would work equally well for those cases where rustc is doing
+// the final linking.
+
+void* __rdl_alloc(size_t, size_t);
+void __rdl_dealloc(void*);
+void* __rdl_realloc(void*, size_t, size_t, size_t);
+void* __rdl_alloc_zeroed(size_t, size_t);
+
+void* __rust_alloc(size_t a, size_t b) {
+  return __rdl_alloc(a, b);
+}
+
+void __rust_dealloc(void* a) {
+  __rdl_dealloc(a);
+}
+
+void* __rust_realloc(void* a, size_t b, size_t c, size_t d) {
+  return __rdl_realloc(a, b, c, d);
+}
+
+void* __rust_alloc_zeroed(size_t a, size_t b) {
+  return __rdl_alloc_zeroed(a, b);
+}
+
+void __rust_alloc_error_handler(size_t a, size_t b) {
+  IMMEDIATE_CRASH();
+}