diff --git a/pkgs/development/compilers/llvm/18/clang/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/18/clang/gnu-install-dirs.patch
index 9185f4b03b84..9517df973ad0 100644
--- a/pkgs/development/compilers/llvm/18/clang/gnu-install-dirs.patch
+++ b/pkgs/development/compilers/llvm/18/clang/gnu-install-dirs.patch
@@ -1,30 +1,3 @@
-diff --git a/CMakeLists.txt b/CMakeLists.txt
-index f7936d72e088..a362fa49b534 100644
---- a/CMakeLists.txt
-+++ b/CMakeLists.txt
-@@ -31,7 +31,21 @@ if(CLANG_BUILT_STANDALONE)
-   find_package(LLVM REQUIRED HINTS "${LLVM_CMAKE_DIR}")
-   list(APPEND CMAKE_MODULE_PATH "${LLVM_DIR}")
- 
--  # Turn into CACHE PATHs for overwritting
-+  # We can't check LLVM_CONFIG here, because find_package(LLVM ...) also sets
-+  # LLVM_CONFIG.
-+  if (NOT LLVM_CONFIG_FOUND)
-+    # Pull values from LLVMConfig.cmake.  We can drop this once the llvm-config
-+    # path is removed.
-+    set(INCLUDE_DIRS ${LLVM_INCLUDE_DIRS})
-+    set(LLVM_OBJ_DIR "${LLVM_BINARY_DIR}")
-+    # N.B. this is just a default value, the CACHE PATHs below can be overriden.
-+    set(MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm")
-+    set(TOOLS_BINARY_DIR "${LLVM_TOOLS_BINARY_DIR}")
-+    set(LIBRARY_DIR "${LLVM_LIBRARY_DIR}")
-+  else()
-+    set(INCLUDE_DIRS "${LLVM_BINARY_DIR}/include" "${MAIN_INCLUDE_DIR}")
-+  endif()
-+
-   set(LLVM_INCLUDE_DIRS ${LLVM_INCLUDE_DIRS} CACHE PATH "Path to llvm/include and any other header dirs needed")
-   set(LLVM_BINARY_DIR "${LLVM_BINARY_DIR}" CACHE PATH "Path to LLVM build tree")
-   set(LLVM_MAIN_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../llvm" CACHE PATH "Path to LLVM source tree")
 diff --git a/cmake/modules/AddClang.cmake b/cmake/modules/AddClang.cmake
 index 75b0080f6715..c895b884cd27 100644
 --- a/cmake/modules/AddClang.cmake
diff --git a/pkgs/development/compilers/llvm/18/compiler-rt/default.nix b/pkgs/development/compilers/llvm/18/compiler-rt/default.nix
index 5a0e3c2e52ce..f51316beb570 100644
--- a/pkgs/development/compilers/llvm/18/compiler-rt/default.nix
+++ b/pkgs/development/compilers/llvm/18/compiler-rt/default.nix
@@ -90,8 +90,6 @@ stdenv.mkDerivation {
     # ld-wrapper dislikes `-rpath-link //nix/store`, so we normalize away the
     # extra `/`.
     ./normalize-var.patch
-    # Prevent a compilation error on darwin
-    ./darwin-targetconditionals.patch
     # See: https://github.com/NixOS/nixpkgs/pull/186575
     ../../common/compiler-rt/darwin-plistbuddy-workaround.patch
     # See: https://github.com/NixOS/nixpkgs/pull/194634#discussion_r999829893
diff --git a/pkgs/development/compilers/llvm/18/libcxx/default.nix b/pkgs/development/compilers/llvm/18/libcxx/default.nix
index 4e3404dbe194..d6c304c0b476 100644
--- a/pkgs/development/compilers/llvm/18/libcxx/default.nix
+++ b/pkgs/development/compilers/llvm/18/libcxx/default.nix
@@ -1,5 +1,5 @@
 { lib, stdenv, llvm_meta
-, monorepoSrc, runCommand, fetchpatch
+, monorepoSrc, runCommand
 , cmake, lndir, ninja, python3, fixDarwinDylibNames, version
 , cxxabi ? if stdenv.hostPlatform.isFreeBSD then libcxxrt else null
 , libcxxrt, libunwind
@@ -19,11 +19,11 @@ let
   # Note: useLLVM is likely false for Darwin but true under pkgsLLVM
   useLLVM = stdenv.hostPlatform.useLLVM or false;
 
-  cxxabiCMakeFlags = lib.optionals (useLLVM && !stdenv.hostPlatform.isWasm) [
-    "-DLIBCXXABI_USE_COMPILER_RT=ON"
-    "-DLIBCXXABI_USE_LLVM_UNWINDER=ON"
-  ] ++ lib.optionals (lib.versionAtLeast version "18" && !(useLLVM && !stdenv.hostPlatform.isWasm)) [
+  cxxabiCMakeFlags = [
     "-DLIBCXXABI_USE_LLVM_UNWINDER=OFF"
+  ] ++ lib.optionals (useLLVM && !stdenv.hostPlatform.isWasm) [
+    "-DLIBCXXABI_ADDITIONAL_LIBRARIES=unwind"
+    "-DLIBCXXABI_USE_COMPILER_RT=ON"
   ] ++ lib.optionals stdenv.hostPlatform.isWasm [
     "-DLIBCXXABI_ENABLE_THREADS=OFF"
     "-DLIBCXXABI_ENABLE_EXCEPTIONS=OFF"
@@ -87,18 +87,6 @@ stdenv.mkDerivation rec {
   patches = lib.optionals (stdenv.isDarwin && lib.versionOlder stdenv.hostPlatform.darwinMinVersion "10.13") [
     # https://github.com/llvm/llvm-project/issues/64226
     ./0001-darwin-10.12-mbstate_t-fix.patch
-  ] ++ lib.optionals (cxxabi == null && lib.versionAtLeast version "18") [
-    # Allow building libcxxabi alone when using LLVM unwinder
-    (fetchpatch {
-      url = "https://github.com/llvm/llvm-project/commit/77610dd10454e87bb387040d2b51100a17ac5755.patch";
-      revert = true;
-      hash = "sha256-jFbC3vBY3nKfjknJ7UzaPyoy0iSYdD3+jUmOFeOaVcA=";
-    })
-    (fetchpatch {
-      url = "https://github.com/llvm/llvm-project/commit/48e5b5ea92674ded69b998cf35724d9012c0f57d.patch";
-      revert = true;
-      hash = "sha256-WN63L4T3GxVozPZb6kx21AgNe4rwwSUOeeryIGsvQYY=";
-    })
   ];
 
   postPatch = ''
diff --git a/pkgs/development/compilers/llvm/18/libunwind/default.nix b/pkgs/development/compilers/llvm/18/libunwind/default.nix
index a3c8e2594f5a..e67823ffb85c 100644
--- a/pkgs/development/compilers/llvm/18/libunwind/default.nix
+++ b/pkgs/development/compilers/llvm/18/libunwind/default.nix
@@ -27,15 +27,6 @@ stdenv.mkDerivation rec {
 
   sourceRoot = "${src.name}/runtimes";
 
-  prePatch = ''
-    cd ../${pname}
-    chmod -R u+w .
-  '';
-
-  postPatch = ''
-    cd ../runtimes
-  '';
-
   postInstall = lib.optionalString (enableShared && !stdenv.hostPlatform.isDarwin) ''
     # libcxxabi wants to link to libunwind_shared.so (?).
     ln -s $out/lib/libunwind.so $out/lib/libunwind_shared.so
diff --git a/pkgs/development/compilers/llvm/18/lld/default.nix b/pkgs/development/compilers/llvm/18/lld/default.nix
index 775eb94701b1..24ff0933dd1d 100644
--- a/pkgs/development/compilers/llvm/18/lld/default.nix
+++ b/pkgs/development/compilers/llvm/18/lld/default.nix
@@ -27,6 +27,10 @@ stdenv.mkDerivation rec {
   nativeBuildInputs = [ cmake ninja ];
   buildInputs = [ libllvm libxml2 ];
 
+  patches = [
+    ./gnu-install-dirs.patch
+  ];
+
   cmakeFlags = [
     "-DLLD_INSTALL_PACKAGE_DIR=${placeholder "dev"}/lib/cmake/lld"
   ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform) [
diff --git a/pkgs/development/compilers/llvm/18/lld/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/18/lld/gnu-install-dirs.patch
new file mode 100644
index 000000000000..6c73a240ab6d
--- /dev/null
+++ b/pkgs/development/compilers/llvm/18/lld/gnu-install-dirs.patch
@@ -0,0 +1,15 @@
+diff --git a/cmake/modules/AddLLD.cmake b/cmake/modules/AddLLD.cmake
+index d3924f7243d4..42a7cd62281c 100644
+--- a/cmake/modules/AddLLD.cmake
++++ b/cmake/modules/AddLLD.cmake
+@@ -18,8 +18,8 @@ macro(add_lld_library name)
+     install(TARGETS ${name}
+       COMPONENT ${name}
+       ${export_to_lldtargets}
+-      LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
+-      ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX}
++      LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}"
++      ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}"
+       RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
+ 
+     if (${ARG_SHARED} AND NOT CMAKE_CONFIGURATION_TYPES)
diff --git a/pkgs/development/compilers/llvm/18/llvm/default.nix b/pkgs/development/compilers/llvm/18/llvm/default.nix
index 94b4d0116173..670171a707f9 100644
--- a/pkgs/development/compilers/llvm/18/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/18/llvm/default.nix
@@ -179,6 +179,10 @@ stdenv.mkDerivation (rec {
     substituteInPlace test/ExecutionEngine/Interpreter/intrinsics.ll \
       --replace "%roundeven32 = call float @llvm.roundeven.f32(float 0.000000e+00)" "" \
       --replace "%roundeven64 = call double @llvm.roundeven.f64(double 0.000000e+00)" ""
+
+    # fails when run in sandbox
+    substituteInPlace unittests/Support/VirtualFileSystemTest.cpp \
+      --replace "PhysicalFileSystemWorkingDirFailure" "DISABLED_PhysicalFileSystemWorkingDirFailure"
   '' + optionalString (stdenv.isDarwin && stdenv.hostPlatform.isx86) ''
     # This test fails on darwin x86_64 because `sw_vers` reports a different
     # macOS version than what LLVM finds by reading
@@ -381,6 +385,9 @@ stdenv.mkDerivation (rec {
     substituteInPlace "$dev/lib/cmake/llvm/LLVMConfig.cmake" \
       --replace 'set(LLVM_BINARY_DIR "''${LLVM_INSTALL_PREFIX}")' 'set(LLVM_BINARY_DIR "'"$lib"'")'
   ''
+  + optionalString (stdenv.isDarwin && enableSharedLibraries) ''
+    ln -s $lib/lib/libLLVM.dylib $lib/lib/libLLVM-${release_version}.dylib
+  ''
   + optionalString (stdenv.buildPlatform != stdenv.hostPlatform) ''
     cp NATIVE/bin/llvm-config $dev/bin/llvm-config-native
   '';
diff --git a/pkgs/development/compilers/llvm/18/llvm/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/18/llvm/gnu-install-dirs.patch
index e2122ebf603d..8b89839490ba 100644
--- a/pkgs/development/compilers/llvm/18/llvm/gnu-install-dirs.patch
+++ b/pkgs/development/compilers/llvm/18/llvm/gnu-install-dirs.patch
@@ -40,7 +40,7 @@ index 230620c37027..dd16cab1835e 100644
    if (APPLE)
      set(_install_name_dir INSTALL_NAME_DIR "@rpath")
 -    set(_install_rpath "@loader_path/../lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-+    set(_install_rpath "@loader_path/../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
++    set(_install_rpath ${extra_libdir})
    elseif(${CMAKE_SYSTEM_NAME} MATCHES "AIX" AND BUILD_SHARED_LIBS)
      # $ORIGIN is not interpreted at link time by aix ld.
      # Since BUILD_SHARED_LIBS is only recommended for use by developers,
@@ -72,8 +72,8 @@ index 230620c37027..dd16cab1835e 100644
 +    # As noted in the differential above, an alternative solution is to have
 +    # all rdeps of nixpkgs' LLVM (that use the AddLLVM.cmake machinery) set
 +    # `CMAKE_INSTALL_RPATH`.
-+    set(_build_rpath "\$ORIGIN/../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
-+    set(_install_rpath "\$ORIGIN/../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
++    set(_build_rpath "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
++    set(_install_rpath ${extra_libdir})
      if(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)")
        set_property(TARGET ${name} APPEND_STRING PROPERTY
                     LINK_FLAGS " -Wl,-z,origin ")
@@ -86,10 +86,10 @@ index 891c9e6d618c..8d963f3b0069 100644
  
    if( APPLE )
 -    set(ocaml_rpath "@executable_path/../../../lib${LLVM_LIBDIR_SUFFIX}")
-+    set(ocaml_rpath "@executable_path/../../../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}")
++    set(ocaml_rpath ${LLVM_LIBRARY_DIR})
    elseif( UNIX )
 -    set(ocaml_rpath "\\$ORIGIN/../../../lib${LLVM_LIBDIR_SUFFIX}")
-+    set(ocaml_rpath "\\$ORIGIN/../../../${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}")
++    set(ocaml_rpath ${LLVM_LIBRARY_DIR})
    endif()
    list(APPEND ocaml_flags "-ldopt" "-Wl,-rpath,${ocaml_rpath}")