Actually we don't need to run llvm-config at all, if we're just hard-coding -lLLVM

debian/patches/dynamic-link-llvm.patch

@@ -1,33 +1,61 @@
+Description: Dynamically link with Debian's LLVM
+ Hard-code -lLLVM, instead of using llvm-config to figure out which components
+ to link in. The latter doesn't work properly anyway for dynamic linking - see
+ LLVM bug #3201. If/when this is fixed, then Rust upstream will probably fix
+ their code to allow for this, and after that happens we can rm this patch.
+ .
+ TODO: not sure if we need extra tweaks for cross-compiling
+Author: Ximin Luo <infinity0@debian.org>
+Forwarded: not-needed
+---
+This patch header follows DEP-3: http://dep.debian.net/deps/dep3/
 --- a/src/librustc_llvm/build.rs
 +++ b/src/librustc_llvm/build.rs
-@@ -125,6 +125,9 @@
-     }
-     cmd.args(&components[..]);
- 
-+    // Link in Debian full LLVM shared library.
-+    println!("cargo:rustc-link-lib={}={}", "dylib", "LLVM");
-+
-     for lib in output(&mut cmd).split_whitespace() {
-         let name = if lib.starts_with("-l") {
-             &lib[2..]
-@@ -143,8 +146,12 @@
-             continue
-         }
+@@ -115,37 +115,10 @@
+        .cpp_link_stdlib(None) // we handle this below
+        .compile("librustllvm.a");
  
+-    // Link in all LLVM libraries, if we're uwring the "wrong" llvm-config then
+-    // we don't pick up system libs because unfortunately they're for the host
+-    // of llvm-config, not the target that we're attempting to link.
+-    let mut cmd = Command::new(&llvm_config);
+-    cmd.arg("--libs");
+-    if !is_crossed {
+-        cmd.arg("--system-libs");
+-    }
+-    cmd.args(&components[..]);
+-
+-    for lib in output(&mut cmd).split_whitespace() {
+-        let name = if lib.starts_with("-l") {
+-            &lib[2..]
+-        } else if lib.starts_with("-") {
+-            &lib[1..]
+-        } else {
+-            continue
+-        };
+-
+-        // Don't need or want this library, but LLVM's CMake build system
+-        // doesn't provide a way to disable it, so filter it here even though we
+-        // may or may not have built it. We don't reference anything from this
+-        // library and it otherwise may just pull in extra dependencies on
+-        // libedit which we don't want
+-        if name == "LLVMLineEditor" {
+-            continue
+-        }
+-
 -        let kind = if name.starts_with("LLVM") {"static"} else {"dylib"};
 -        println!("cargo:rustc-link-lib={}={}", kind, name);
-+        // On Debian we ignore the LLVM component static libs, and instead
-+        // dynamically link in the full LLVM shared library, above.
-+        // See #832565 for more details
-+        if !name.starts_with("LLVM") {
-+            println!("cargo:rustc-link-lib={}={}", "dylib", name);
-+        }
-     }
+-    }
++    // Link in all LLVM libraries
++    // Link in Debian full LLVM shared library.
++    // TODO: not sure what to do in the cross-compiling case.
++    println!("cargo:rustc-link-lib={}={}", "dylib", "LLVM");
  
      // LLVM ldflags
+     //
 --- a/src/etc/mklldeps.py
 +++ b/src/etc/mklldeps.py
-@@ -56,16 +56,14 @@
+@@ -56,31 +56,12 @@
  
  f.write("\n")
  
@@ -39,27 +67,27 @@
 +llvm_shared = True
  
  # LLVM libs
- args = [llvm_config, '--libs', '--system-libs']
- args.extend(components)
- out = run(args)
-+# Link in Debian full LLVM shared library.
-+f.write("#[link(name = \"LLVM\")]\n")
- for lib in out.strip().replace("\n", ' ').split(' '):
-     if len(lib) == 0:
-         continue
-@@ -77,10 +75,11 @@
-         lib = lib.strip()[2:]
-     elif lib[0] == '-':
-         lib = lib.strip()[1:]
+-args = [llvm_config, '--libs', '--system-libs']
+-args.extend(components)
+-out = run(args)
+-for lib in out.strip().replace("\n", ' ').split(' '):
+-    if len(lib) == 0:
+-        continue
+-    # in some cases we get extra spaces in between libs so ignore those
+-    if len(lib) == 1 and lib == ' ':
+-        continue
+-    # not all libs strictly follow -lfoo, on Bitrig, there is -pthread
+-    if lib[0:2] == '-l':
+-        lib = lib.strip()[2:]
+-    elif lib[0] == '-':
+-        lib = lib.strip()[1:]
 -    f.write("#[link(name = \"" + lib + "\"")
 -    if not llvm_shared and 'LLVM' in lib:
 -        f.write(", kind = \"static\"")
 -    f.write(")]\n")
-+    # On Debian we ignore the LLVM component static libs, and instead
-+    # dynamically link in the full LLVM shared library, above.
-+    # See #832565 for more details
-+    if not 'LLVM' in lib:
-+        f.write("#[link(name = \"" + lib + "\")]\n")
++# Link in Debian full LLVM shared library.
++# TODO: not sure what to do in the cross-compiling case.
++f.write("#[link(name = \"LLVM\")]\n")
  
  # LLVM ldflags
  out = run([llvm_config, '--ldflags'])