From 48f205d496213ac64e7596b1e3e3807b28833e14 Mon Sep 17 00:00:00 2001
From: Petr Hosek <phosek@google.com>
Date: Sun, 9 Jun 2019 16:28:25 -0700
Subject: [PATCH] Pass LLVM linker flags to librustc_llvm build

Some -L and -l flags may be needed even when building librustc_llvm,
for example when using static libc++ on Linux we may need to manually
specify the library search path and -ldl -lpthread as additional link
dependencies. We pass LLVM linker flags from config to librustc_llvm
build to make sure these cases are handled.
---
 src/bootstrap/compile.rs   |  4 ++++
 src/librustc_llvm/build.rs | 15 +++++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/src/bootstrap/compile.rs b/src/bootstrap/compile.rs
index c7fa8e788b573..576267e6948f5 100644
--- a/src/bootstrap/compile.rs
+++ b/src/bootstrap/compile.rs
@@ -775,6 +775,10 @@ pub fn build_codegen_backend(builder: &Builder<'_>,
                     cargo.env("CFG_LLVM_ROOT", s);
                 }
             }
+            // Some LLVM linker flags (-L and -l) may be needed to link librustc_llvm.
+            if let Some(ref s) = builder.config.llvm_ldflags {
+                cargo.env("LLVM_LINKER_FLAGS", s);
+            }
             // Building with a static libstdc++ is only supported on linux right now,
             // not for MSVC or macOS
             if builder.config.llvm_static_stdcpp &&
diff --git a/src/librustc_llvm/build.rs b/src/librustc_llvm/build.rs
index 7fa83dd977950..21fa872c8dadb 100644
--- a/src/librustc_llvm/build.rs
+++ b/src/librustc_llvm/build.rs
@@ -234,6 +234,21 @@ fn main() {
         }
     }
 
+    // Some LLVM linker flags (-L and -l) may be needed even when linking
+    // librustc_llvm, for example when using static libc++, we may need to
+    // manually specify the library search path and -ldl -lpthread as link
+    // dependencies.
+    let llvm_linker_flags = env::var_os("LLVM_LINKER_FLAGS");
+    if let Some(s) = llvm_linker_flags {
+        for lib in s.into_string().unwrap().split_whitespace() {
+            if lib.starts_with("-l") {
+                println!("cargo:rustc-link-lib={}", &lib[2..]);
+            } else if lib.starts_with("-L") {
+                println!("cargo:rustc-link-search=native={}", &lib[2..]);
+            }
+        }
+    }
+
     let llvm_static_stdcpp = env::var_os("LLVM_STATIC_STDCPP");
     let llvm_use_libcxx = env::var_os("LLVM_USE_LIBCXX");