From 77b6476d8e5bcbcec930b81522c446c0211dbe03 Mon Sep 17 00:00:00 2001
From: "Kirill A. Korinsky" <kirill@korins.ky>
Date: Fri, 4 Feb 2022 03:44:38 +0100
Subject: [PATCH] Introduce `llvm-enable-rtti` option

This option is controls when LLVM build adds `-fno-rtti`. Some details
available here: https://www.llvm.org/docs/HowToSetUpLLVMStyleRTTI.html

When this option is enabled, llvm build produces a bit more symbols:
````
rust % nm build/x86_64-apple-darwin/llvm/lib/libLLVMCore.a | grep llvm10CallbackVHE
0000000000007120 S __ZTIN4llvm10CallbackVHE
0000000000007240 S __ZTSN4llvm10CallbackVHE
00000000000070e8 S __ZTVN4llvm10CallbackVHE
````
and just to compare the same build without this option (current behaviour):
```
rust % nm build/x86_64-apple-darwin/llvm/lib/libLLVMCore.a | grep llvm10CallbackVHE
00000000000070b8 S __ZTVN4llvm10CallbackVHE
```

An attempt to bootstrap `rust` with `clang` which was built with enabled
RTTI may fail with linking error like:
```
 = note: dyld: Symbol not found: __ZTIN4llvm10CallbackVHE
            Referenced from: /opt/local/libexec/llvm-9.0/bin/../lib/libclang-cpp.dylib
            Expected in: .../build/x86_64-apple-darwin/stage2/lib/libLLVM.dylib
           in /opt/local/libexec/llvm-9.0/bin/../lib/libclang-cpp.dylib
```
---
 config.toml.example        | 3 +++
 src/bootstrap/config.rs    | 4 ++++
 src/bootstrap/configure.py | 1 +
 src/bootstrap/native.rs    | 4 ++++
 4 files changed, 12 insertions(+)

diff --git a/config.toml.example b/config.toml.example
index f24f8e81a7944..193a9020a55bd 100644
--- a/config.toml.example
+++ b/config.toml.example
@@ -148,6 +148,9 @@ changelog-seen = 2
 # The value specified here will be passed as `-DLLVM_USE_LINKER` to CMake.
 #use-linker = <none> (path)
 
+# Whether or not to specify `-DLLVM_ENABLE_RTTI=YES`
+#enable-rtti = false
+
 # Whether or not to specify `-DLLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN=YES`
 #allow-old-toolchain = false
 
diff --git a/src/bootstrap/config.rs b/src/bootstrap/config.rs
index 683cfc630e771..f73d445469a0d 100644
--- a/src/bootstrap/config.rs
+++ b/src/bootstrap/config.rs
@@ -105,6 +105,7 @@ pub struct Config {
     pub llvm_version_suffix: Option<String>,
     pub llvm_use_linker: Option<String>,
     pub llvm_allow_old_toolchain: bool,
+    pub llvm_enable_rtti: bool,
     pub llvm_polly: bool,
     pub llvm_clang: bool,
     pub llvm_from_ci: bool,
@@ -474,6 +475,7 @@ derive_merge! {
         use_libcxx: Option<bool>,
         use_linker: Option<String>,
         allow_old_toolchain: Option<bool>,
+        enable_rtti: Option<bool>,
         polly: Option<bool>,
         clang: Option<bool>,
         download_ci_llvm: Option<StringOrBool>,
@@ -805,6 +807,7 @@ impl Config {
             set(&mut config.llvm_use_libcxx, llvm.use_libcxx);
             config.llvm_use_linker = llvm.use_linker.clone();
             config.llvm_allow_old_toolchain = llvm.allow_old_toolchain.unwrap_or(false);
+            config.llvm_enable_rtti = llvm.enable_rtti.unwrap_or(false);
             config.llvm_polly = llvm.polly.unwrap_or(false);
             config.llvm_clang = llvm.clang.unwrap_or(false);
             config.llvm_from_ci = match llvm.download_ci_llvm {
@@ -874,6 +877,7 @@ impl Config {
                 check_ci_llvm!(llvm.use_libcxx);
                 check_ci_llvm!(llvm.use_linker);
                 check_ci_llvm!(llvm.allow_old_toolchain);
+                check_ci_llvm!(llvm.enable_rtti);
                 check_ci_llvm!(llvm.polly);
                 check_ci_llvm!(llvm.clang);
                 check_ci_llvm!(llvm.plugins);
diff --git a/src/bootstrap/configure.py b/src/bootstrap/configure.py
index 94424cb4548fa..0385cb94a6786 100755
--- a/src/bootstrap/configure.py
+++ b/src/bootstrap/configure.py
@@ -73,6 +73,7 @@ def v(*args):
 o("optimize", "rust.optimize", "build optimized rust code")
 o("optimize-llvm", "llvm.optimize", "build optimized LLVM")
 o("llvm-assertions", "llvm.assertions", "build LLVM with assertions")
+o("llvm-enable-rtti", "llvm.enable-rtti", "build LLVM with using C++’s built in RTTI")
 o("llvm-plugins", "llvm.plugins", "build LLVM with plugin interface")
 o("debug-assertions", "rust.debug-assertions", "build with debugging assertions")
 o("debug-assertions-std", "rust.debug-assertions-std", "build the standard library with debugging assertions")
diff --git a/src/bootstrap/native.rs b/src/bootstrap/native.rs
index 4a754e6da1209..ed802c74794dd 100644
--- a/src/bootstrap/native.rs
+++ b/src/bootstrap/native.rs
@@ -351,6 +351,10 @@ impl Step for Llvm {
             cfg.define("LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN", "YES");
         }
 
+        if builder.config.llvm_enable_rtti {
+            cfg.define("LLVM_ENABLE_RTTI", "YES");
+        }
+
         configure_cmake(builder, target, &mut cfg, true);
 
         // FIXME: we don't actually need to build all LLVM tools and all LLVM