diff --git a/pkgs/development/compilers/llvm/19/clang/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/19/clang/gnu-install-dirs.patch
new file mode 100644
index 000000000000..b8c1c110cf22
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/clang/gnu-install-dirs.patch
@@ -0,0 +1,71 @@
+diff --git a/cmake/modules/AddClang.cmake b/cmake/modules/AddClang.cmake
+index 75b0080f6..c895b884c 100644
+--- a/cmake/modules/AddClang.cmake
++++ b/cmake/modules/AddClang.cmake
+@@ -119,8 +119,8 @@ macro(add_clang_library name)
+         install(TARGETS ${lib}
+           COMPONENT ${lib}
+           ${export_to_clangtargets}
+-          LIBRARY DESTINATION lib${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 (NOT LLVM_ENABLE_IDE)
+diff --git a/lib/Headers/CMakeLists.txt b/lib/Headers/CMakeLists.txt
+index e6ae4e19e..5ef01aea2 100644
+--- a/lib/Headers/CMakeLists.txt
++++ b/lib/Headers/CMakeLists.txt
+@@ -337,6 +337,7 @@ set(llvm_libc_wrapper_files
+ 
+ include(GetClangResourceDir)
+ get_clang_resource_dir(output_dir PREFIX ${LLVM_LIBRARY_OUTPUT_INTDIR}/.. SUBDIR include)
++set(header_install_dir ${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}/clang/${CLANG_VERSION_MAJOR}/include)
+ set(out_files)
+ set(generated_files)
+ 
+diff --git a/tools/libclang/CMakeLists.txt b/tools/libclang/CMakeLists.txt
+index b5b6d2807..6b592d255 100644
+--- a/tools/libclang/CMakeLists.txt
++++ b/tools/libclang/CMakeLists.txt
+@@ -246,7 +246,7 @@ foreach(PythonVersion ${CLANG_PYTHON_BINDINGS_VERSIONS})
+           COMPONENT
+             libclang-python-bindings
+           DESTINATION
+-            "lib${LLVM_LIBDIR_SUFFIX}/python${PythonVersion}/site-packages")
++            "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}/python${PythonVersion}/site-packages")
+ endforeach()
+ if(NOT LLVM_ENABLE_IDE)
+   add_custom_target(libclang-python-bindings)
+diff --git a/tools/scan-build-py/CMakeLists.txt b/tools/scan-build-py/CMakeLists.txt
+index 3aca22c0b..3115353e3 100644
+--- a/tools/scan-build-py/CMakeLists.txt
++++ b/tools/scan-build-py/CMakeLists.txt
+@@ -88,7 +88,7 @@ foreach(lib ${LibScanbuild})
+                      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/lib/libscanbuild/${lib})
+   list(APPEND Depends ${CMAKE_BINARY_DIR}/lib/libscanbuild/${lib})
+   install(FILES lib/libscanbuild/${lib}
+-          DESTINATION lib${CLANG_LIBDIR_SUFFIX}/libscanbuild
++          DESTINATION "${CMAKE_INSTALL_LIBDIR}/libscanbuild"
+           COMPONENT scan-build-py)
+ endforeach()
+ 
+@@ -106,7 +106,7 @@ foreach(resource ${LibScanbuildResources})
+                      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/lib/libscanbuild/resources/${resource})
+   list(APPEND Depends ${CMAKE_BINARY_DIR}/lib/libscanbuild/resources/${resource})
+   install(FILES lib/libscanbuild/resources/${resource}
+-          DESTINATION lib${CLANG_LIBDIR_SUFFIX}/libscanbuild/resources
++          DESTINATION "${CMAKE_INSTALL_LIBDIR}/libscanbuild/resources"
+           COMPONENT scan-build-py)
+ endforeach()
+ 
+@@ -122,7 +122,7 @@ foreach(lib ${LibEar})
+                      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/lib/libear/${lib})
+   list(APPEND Depends ${CMAKE_BINARY_DIR}/lib/libear/${lib})
+   install(FILES lib/libear/${lib}
+-          DESTINATION lib${CLANG_LIBDIR_SUFFIX}/libear
++          DESTINATION "${CMAKE_INSTALL_LIBDIR}/libear"
+           COMPONENT scan-build-py)
+ endforeach()
+ 
diff --git a/pkgs/development/compilers/llvm/19/clang/purity.patch b/pkgs/development/compilers/llvm/19/clang/purity.patch
new file mode 100644
index 000000000000..5ce14a3479a0
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/clang/purity.patch
@@ -0,0 +1,25 @@
+From 4add81bba40dcec62c4ea4481be8e35ac53e89d8 Mon Sep 17 00:00:00 2001
+From: Will Dietz <w@wdtz.org>
+Date: Thu, 18 May 2017 11:56:12 -0500
+Subject: [PATCH] "purity" patch for 5.0
+
+---
+ lib/Driver/ToolChains/Gnu.cpp | 3 ---
+ 1 file changed, 3 deletions(-)
+
+diff --git a/lib/Driver/ToolChains/Gnu.cpp b/lib/Driver/ToolChains/Gnu.cpp
+index fe3c0191bb..c6a482bece 100644
+--- a/lib/Driver/ToolChains/Gnu.cpp
++++ b/lib/Driver/ToolChains/Gnu.cpp
+@@ -446,9 +446,6 @@ void tools::gnutools::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+                            ToolChain.isPIEDefault(Args));
+       if (IsPIE)
+         CmdArgs.push_back("-pie");
+-      CmdArgs.push_back("-dynamic-linker");
+-      CmdArgs.push_back(Args.MakeArgString(Twine(D.DyldPrefix) +
+-                                           ToolChain.getDynamicLinker(Args)));
+     }
+   }
+ 
+-- 
+2.11.0
diff --git a/pkgs/development/compilers/llvm/19/compiler-rt/X86-support-extension.patch b/pkgs/development/compilers/llvm/19/compiler-rt/X86-support-extension.patch
new file mode 100644
index 000000000000..07013e5a6825
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/compiler-rt/X86-support-extension.patch
@@ -0,0 +1,21 @@
+diff --git a/lib/builtins/CMakeLists.txt b/lib/builtins/CMakeLists.txt
+index 3a66dd9c3fb..7efc85d9f9f 100644
+--- a/lib/builtins/CMakeLists.txt
++++ b/lib/builtins/CMakeLists.txt
+@@ -348,4 +348,8 @@ if (NOT MSVC)
+ 
++  set(i486_SOURCES ${i386_SOURCES})
++  set(i586_SOURCES ${i386_SOURCES})
++  set(i686_SOURCES ${i386_SOURCES})
++
+   if (WIN32)
+     set(i386_SOURCES
+       ${i386_SOURCES}
+@@ -723,6 +723,7 @@ else ()
+   endif()
+ 
+   foreach (arch ${BUILTIN_SUPPORTED_ARCH})
++      message("arch: ${arch}")
+     if (CAN_TARGET_${arch})
+       # For ARM archs, exclude any VFP builtins if VFP is not supported
+       if (${arch} MATCHES "^(arm|armhf|armv7|armv7s|armv7k|armv7m|armv7em)$")
diff --git a/pkgs/development/compilers/llvm/19/compiler-rt/darwin-targetconditionals.patch b/pkgs/development/compilers/llvm/19/compiler-rt/darwin-targetconditionals.patch
new file mode 100644
index 000000000000..425dc2af01e7
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/compiler-rt/darwin-targetconditionals.patch
@@ -0,0 +1,71 @@
+diff --git a/lib/sanitizer_common/sanitizer_mac.cpp b/lib/sanitizer_common/sanitizer_mac.cpp
+--- a/lib/sanitizer_common/sanitizer_mac.cpp
++++ b/lib/sanitizer_common/sanitizer_mac.cpp
+@@ -613,9 +613,15 @@ HandleSignalMode GetHandleSignalMode(int signum) {
+ // Offset example:
+ // XNU 17 -- macOS 10.13 -- iOS 11 -- tvOS 11 -- watchOS 4
+ constexpr u16 GetOSMajorKernelOffset() {
+-  if (TARGET_OS_OSX) return 4;
+-  if (TARGET_OS_IOS || TARGET_OS_TV) return 6;
+-  if (TARGET_OS_WATCH) return 13;
++#if TARGET_OS_OSX
++  return 4;
++#endif
++#if TARGET_OS_IOS || TARGET_OS_TV
++  return 6;
++#endif
++#if TARGET_OS_WATCH
++  return 13;
++#endif
+ }
+ 
+ using VersStr = char[64];
+@@ -627,13 +633,13 @@ static uptr ApproximateOSVersionViaKernelVersion(VersStr vers) {
+   u16 os_major = kernel_major - offset;
+ 
+   const char *format = "%d.0";
+-  if (TARGET_OS_OSX) {
+-    if (os_major >= 16) {  // macOS 11+
+-      os_major -= 5;
+-    } else {  // macOS 10.15 and below
+-      format = "10.%d";
+-    }
++#if TARGET_OS_OSX
++  if (os_major >= 16) {  // macOS 11+
++    os_major -= 5;
++  } else {  // macOS 10.15 and below
++    format = "10.%d";
+   }
++#endif
+   return internal_snprintf(vers, sizeof(VersStr), format, os_major);
+ }
+ 
+@@ -681,15 +687,14 @@ void ParseVersion(const char *vers, u16 *major, u16 *minor) {
+ // Aligned versions example:
+ // macOS 10.15 -- iOS 13 -- tvOS 13 -- watchOS 6
+ static void MapToMacos(u16 *major, u16 *minor) {
+-  if (TARGET_OS_OSX)
+-    return;
+-
+-  if (TARGET_OS_IOS || TARGET_OS_TV)
++#if !TARGET_OS_OSX
++#if TARGET_OS_IOS || TARGET_OS_TV
+     *major += 2;
+-  else if (TARGET_OS_WATCH)
++#elif TARGET_OS_WATCH
+     *major += 9;
+-  else
++#else
+     UNREACHABLE("unsupported platform");
++#endif
+ 
+   if (*major >= 16) {  // macOS 11+
+     *major -= 5;
+@@ -697,6 +702,7 @@ static void MapToMacos(u16 *major, u16 *minor) {
+     *minor = *major;
+     *major = 10;
+   }
++#endif
+ }
+ 
+ static MacosVersion GetMacosAlignedVersionInternal() {
diff --git a/pkgs/development/compilers/llvm/19/compiler-rt/normalize-var.patch b/pkgs/development/compilers/llvm/19/compiler-rt/normalize-var.patch
new file mode 100644
index 000000000000..2b25fd4a0744
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/compiler-rt/normalize-var.patch
@@ -0,0 +1,16 @@
+diff --git a/cmake/Modules/CompilerRTUtils.cmake b/cmake/Modules/CompilerRTUtils.cmake
+index 4c85551d7766..297d7a47c54b 100644
+--- a/cmake/Modules/CompilerRTUtils.cmake
++++ b/cmake/Modules/CompilerRTUtils.cmake
+@@ -328,8 +328,9 @@ macro(load_llvm_config)
+     endif()
+   endif()
+ 
+-  set(LLVM_LIBRARY_OUTPUT_INTDIR
+-    ${LLVM_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX})
++  get_filename_component(LLVM_LIBRARY_OUTPUT_INTDIR
++    ${LLVM_BINARY_DIR}/${CMAKE_CFG_INTDIR}/lib${LLVM_LIBDIR_SUFFIX}
++    REALPATH)
+ 
+   set(LLVM_MAIN_SRC_DIR "${LLVM_MAIN_SRC_DIR_DEFAULT}" CACHE PATH "Path to LLVM source tree")
+   message(STATUS "LLVM_MAIN_SRC_DIR: \"${LLVM_MAIN_SRC_DIR}\"")
diff --git a/pkgs/development/compilers/llvm/19/libcxx/0001-darwin-10.12-mbstate_t-fix.patch b/pkgs/development/compilers/llvm/19/libcxx/0001-darwin-10.12-mbstate_t-fix.patch
new file mode 100644
index 000000000000..29942f8ed03d
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/libcxx/0001-darwin-10.12-mbstate_t-fix.patch
@@ -0,0 +1,31 @@
+From 9c1cb26c1dd3f92d1c1177e548107d2cd3c5e616 Mon Sep 17 00:00:00 2001
+From: annalee <150648636+a-n-n-a-l-e-e@users.noreply.github.com>
+Date: Fri, 23 Feb 2024 22:58:58 +0000
+Subject: [PATCH] darwin 10.12 mbstate_t fix
+
+https://github.com/llvm/llvm-project/issues/64226
+
+removes space from
+https://github.com/macports/macports-ports/raw/acd8acb171f1658596ed1cf25da48d5b932e2d19/lang/llvm-17/files/0042-mbstate_t-not-defined.patch
+so it applies cleanly
+---
+ libcxx/include/__mbstate_t.h | 3 +++
+ 1 file changed, 3 insertions(+)
+
+diff --git a/libcxx/include/__mbstate_t.h b/libcxx/include/__mbstate_t.h
+index bfa6d61..5f51112 100644
+--- a/libcxx/include/__mbstate_t.h
++++ b/libcxx/include/__mbstate_t.h
+@@ -42,6 +42,9 @@
+ #elif __has_include(<bits/types/mbstate_t.h>)
+ #  include <bits/types/mbstate_t.h> // works on most Unixes
+ #elif __has_include(<sys/_types/_mbstate_t.h>)
++#  if __has_include(<machine/_types.h>)
++#    include <machine/_types.h>
++#  endif
+ #  include <sys/_types/_mbstate_t.h> // works on Darwin
+ #elif !defined(_LIBCPP_HAS_NO_WIDE_CHARACTERS) && __has_include_next(<wchar.h>)
+ #  include_next <wchar.h> // fall back to the C standard provider of mbstate_t
+-- 
+2.43.0
+
diff --git a/pkgs/development/compilers/llvm/19/lld/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/19/lld/gnu-install-dirs.patch
new file mode 100644
index 000000000000..6c73a240ab6d
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/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/19/lldb/cpu_subtype_arm64e_replacement.patch b/pkgs/development/compilers/llvm/19/lldb/cpu_subtype_arm64e_replacement.patch
new file mode 100644
index 000000000000..20d35c9f3ea9
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/lldb/cpu_subtype_arm64e_replacement.patch
@@ -0,0 +1,12 @@
+diff --git a/source/Host/macosx/objcxx/HostInfoMacOSX.mm b/source/Host/macosx/objcxx/HostInfoMacOSX.mm
+--- a/source/Host/macosx/objcxx/HostInfoMacOSX.mm
++++ b/source/Host/macosx/objcxx/HostInfoMacOSX.mm
+@@ -233,7 +233,7 @@ void HostInfoMacOSX::ComputeHostArchitectureSupport(ArchSpec &arch_32,
+     len = sizeof(is_64_bit_capable);
+     ::sysctlbyname("hw.cpu64bit_capable", &is_64_bit_capable, &len, NULL, 0);
+ 
+-    if (cputype == CPU_TYPE_ARM64 && cpusubtype == CPU_SUBTYPE_ARM64E) {
++    if (cputype == CPU_TYPE_ARM64 && cpusubtype == ((cpu_subtype_t) 2)) { // CPU_SUBTYPE_ARM64E is not available in the macOS 10.12 headers
+       // The arm64e architecture is a preview. Pretend the host architecture
+       // is arm64.
+       cpusubtype = CPU_SUBTYPE_ARM64_ALL;
diff --git a/pkgs/development/compilers/llvm/19/lldb/procfs.patch b/pkgs/development/compilers/llvm/19/lldb/procfs.patch
new file mode 100644
index 000000000000..7b200e86505c
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/lldb/procfs.patch
@@ -0,0 +1,46 @@
+--- a/source/Plugins/Process/Linux/Procfs.h
++++ b/source/Plugins/Process/Linux/Procfs.h
+@@ -10,6 +10,13 @@
+ // sys/procfs.h on Android/Linux for all supported architectures.
+ 
+ #include <sys/ptrace.h>
++#include <asm/ptrace.h>
++
++// on i686 preprocessor symbols with these register names are defined as
++// numeric constants; these symbols clash with identifier names used in
++// `llvm/Support/VirtualFileSystem.h` and `llvm/ADT/SmallVector.h`
++#undef FS
++#undef CS
+ 
+ #include "lldb/lldb-types.h"
+ 
+@@ -17,23 +24,13 @@
+ 
+ #include <vector>
+ 
+-#ifdef __ANDROID__
+-#if defined(__arm64__) || defined(__aarch64__)
+-typedef unsigned long elf_greg_t;
+-typedef elf_greg_t
+-    elf_gregset_t[(sizeof(struct user_pt_regs) / sizeof(elf_greg_t))];
+-typedef struct user_fpsimd_state elf_fpregset_t;
+-#ifndef NT_FPREGSET
+-#define NT_FPREGSET NT_PRFPREG
+-#endif // NT_FPREGSET
+-#elif defined(__mips__)
+-#ifndef NT_FPREGSET
+-#define NT_FPREGSET NT_PRFPREG
+-#endif // NT_FPREGSET
+-#endif
+-#else // __ANDROID__
++#if !defined(__GLIBC__) && defined(__powerpc__)
++#define pt_regs musl_pt_regs
++#include <sys/procfs.h>
++#undef pt_regs
++#else
+ #include <sys/procfs.h>
+-#endif // __ANDROID__
++#endif
+ 
+ namespace lldb_private {
+ namespace process_linux {
diff --git a/pkgs/development/compilers/llvm/19/llvm/gnu-install-dirs-polly.patch b/pkgs/development/compilers/llvm/19/llvm/gnu-install-dirs-polly.patch
new file mode 100644
index 000000000000..6a359bdbefde
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/llvm/gnu-install-dirs-polly.patch
@@ -0,0 +1,13 @@
+--- a/tools/polly/cmake/polly_macros.cmake	2024-03-15 17:36:20.550893344 -0700
++++ b/tools/polly/cmake/polly_macros.cmake	2024-03-15 17:37:06.277332960 -0700
+@@ -45,8 +45,8 @@
+     install(TARGETS ${name}
+       COMPONENT ${name}
+       EXPORT LLVMExports
+-      LIBRARY DESTINATION lib${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})
+     add_llvm_install_targets(install-${name}
+       COMPONENT ${name})
+   endif()
diff --git a/pkgs/development/compilers/llvm/19/llvm/gnu-install-dirs.patch b/pkgs/development/compilers/llvm/19/llvm/gnu-install-dirs.patch
new file mode 100644
index 000000000000..8b89839490ba
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/llvm/gnu-install-dirs.patch
@@ -0,0 +1,137 @@
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 471817d68286..c51463304159 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -1010,7 +1010,7 @@ if (NOT TENSORFLOW_AOT_PATH STREQUAL "")
+   add_subdirectory(${TENSORFLOW_AOT_PATH}/xla_aot_runtime_src
+     ${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}/tf_runtime)
+   install(TARGETS tf_xla_runtime EXPORT LLVMExports
+-    ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX} COMPONENT tf_xla_runtime)
++    ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX} COMPONENT tf_xla_runtime)
+   set_property(GLOBAL APPEND PROPERTY LLVM_EXPORTS tf_xla_runtime)
+   # Once we add more modules, we should handle this more automatically.
+   if (DEFINED LLVM_OVERRIDE_MODEL_HEADER_INLINERSIZEMODEL)
+diff --git a/cmake/modules/AddLLVM.cmake b/cmake/modules/AddLLVM.cmake
+index 230620c37027..dd16cab1835e 100644
+--- a/cmake/modules/AddLLVM.cmake
++++ b/cmake/modules/AddLLVM.cmake
+@@ -876,8 +876,8 @@ macro(add_llvm_library name)
+       get_target_export_arg(${name} LLVM export_to_llvmexports ${umbrella})
+       install(TARGETS ${name}
+               ${export_to_llvmexports}
+-              LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX} COMPONENT ${name}
+-              ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX} COMPONENT ${name}
++              LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" COMPONENT ${name}
++              ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" COMPONENT ${name}
+               RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}" COMPONENT ${name})
+ 
+       if (NOT LLVM_ENABLE_IDE)
+@@ -2069,7 +2069,7 @@ function(llvm_install_library_symlink name dest type)
+     set(LLVM_LINK_OR_COPY copy)
+   endif()
+ 
+-  set(output_dir lib${LLVM_LIBDIR_SUFFIX})
++  set(output_dir ${CMAKE_INSTALL_FULL_LIBDIR}${LLVM_LIBDIR_SUFFIX})
+   if(WIN32 AND "${type}" STREQUAL "SHARED")
+     set(output_dir "${CMAKE_INSTALL_BINDIR}")
+   endif()
+@@ -2344,16 +2344,37 @@ function(llvm_setup_rpath name)
+ 
+   if (APPLE)
+     set(_install_name_dir INSTALL_NAME_DIR "@rpath")
+-    set(_install_rpath "@loader_path/../lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
++    set(_install_rpath ${extra_libdir})
+   elseif(${CMAKE_SYSTEM_NAME} MATCHES "AIX" AND BUILD_SHARED_LIBS)
+     # $ORIGIN is not interpreted at link time by aix ld.
+     # Since BUILD_SHARED_LIBS is only recommended for use by developers,
+     # hardcode the rpath to build/install lib dir first in this mode.
+     # FIXME: update this when there is better solution.
+-    set(_install_rpath "${LLVM_LIBRARY_OUTPUT_INTDIR}" "${CMAKE_INSTALL_PREFIX}/lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
++    set(_install_rpath "${LLVM_LIBRARY_OUTPUT_INTDIR}" "${CMAKE_INSTALL_FULL_LIBDIR}${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
+   elseif(UNIX)
+-    set(_build_rpath "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
+-    set(_install_rpath "\$ORIGIN/../lib${LLVM_LIBDIR_SUFFIX}")
++    # Note that we add `extra_libdir` (aka `LLVM_LIBRARY_DIR` in our case) back
++    # to `_install_rpath` here.
++    #
++    # In nixpkgs we do not build and install LLVM alongside rdeps of LLVM (i.e.
++    # clang); instead LLVM is its own package and thus lands at its own nix
++    # store path. This makes it so that the default relative rpath (`../lib/`)
++    # does not point at the LLVM shared objects.
++    #
++    # More discussion here:
++    #   - https://github.com/NixOS/nixpkgs/pull/235624#discussion_r1220150329
++    #   - https://reviews.llvm.org/D146918 (16.0.5+)
++    #
++    # Note that we leave `extra_libdir` in `_build_rpath`: without FHS there is
++    # no potential that this will result in us pulling in the "wrong" LLVM.
++    # Adding this to the build rpath means we aren't forced to use
++    # `installCheckPhase` instead of `checkPhase` (i.e. binaries in the build
++    # dir, pre-install, will have the right rpath for LLVM).
++    #
++    # 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/../lib${LLVM_LIBDIR_SUFFIX}" ${extra_libdir})
++    set(_install_rpath ${extra_libdir})
+     if(${CMAKE_SYSTEM_NAME} MATCHES "(FreeBSD|DragonFly)")
+       set_property(TARGET ${name} APPEND_STRING PROPERTY
+                    LINK_FLAGS " -Wl,-z,origin ")
+diff --git a/cmake/modules/AddOCaml.cmake b/cmake/modules/AddOCaml.cmake
+index 891c9e6d618c..8d963f3b0069 100644
+--- a/cmake/modules/AddOCaml.cmake
++++ b/cmake/modules/AddOCaml.cmake
+@@ -147,9 +147,9 @@ function(add_ocaml_library name)
+   endforeach()
+ 
+   if( APPLE )
+-    set(ocaml_rpath "@executable_path/../../../lib${LLVM_LIBDIR_SUFFIX}")
++    set(ocaml_rpath ${LLVM_LIBRARY_DIR})
+   elseif( UNIX )
+-    set(ocaml_rpath "\\$ORIGIN/../../../lib${LLVM_LIBDIR_SUFFIX}")
++    set(ocaml_rpath ${LLVM_LIBRARY_DIR})
+   endif()
+   list(APPEND ocaml_flags "-ldopt" "-Wl,-rpath,${ocaml_rpath}")
+ 
+diff --git a/cmake/modules/CMakeLists.txt b/cmake/modules/CMakeLists.txt
+index d99af79aa38e..21e794224b99 100644
+--- a/cmake/modules/CMakeLists.txt
++++ b/cmake/modules/CMakeLists.txt
+@@ -127,7 +127,7 @@ set(LLVM_CONFIG_INCLUDE_DIRS
+   )
+ list(REMOVE_DUPLICATES LLVM_CONFIG_INCLUDE_DIRS)
+ 
+-extend_path(LLVM_CONFIG_LIBRARY_DIR "\${LLVM_INSTALL_PREFIX}" "lib\${LLVM_LIBDIR_SUFFIX}")
++extend_path(LLVM_CONFIG_LIBRARY_DIR "\${LLVM_INSTALL_PREFIX}" "${CMAKE_INSTALL_LIBDIR}\${LLVM_LIBDIR_SUFFIX}")
+ set(LLVM_CONFIG_LIBRARY_DIRS
+   "${LLVM_CONFIG_LIBRARY_DIR}"
+   # FIXME: Should there be other entries here?
+diff --git a/tools/llvm-config/BuildVariables.inc.in b/tools/llvm-config/BuildVariables.inc.in
+index 370005cd8d7d..7e790bc52111 100644
+--- a/tools/llvm-config/BuildVariables.inc.in
++++ b/tools/llvm-config/BuildVariables.inc.in
+@@ -23,6 +23,7 @@
+ #define LLVM_CXXFLAGS "@LLVM_CXXFLAGS@"
+ #define LLVM_BUILDMODE "@LLVM_BUILDMODE@"
+ #define LLVM_LIBDIR_SUFFIX "@LLVM_LIBDIR_SUFFIX@"
++#define LLVM_INSTALL_LIBDIR "@CMAKE_INSTALL_LIBDIR@"
+ #define LLVM_INSTALL_INCLUDEDIR "@CMAKE_INSTALL_INCLUDEDIR@"
+ #define LLVM_INSTALL_PACKAGE_DIR "@LLVM_INSTALL_PACKAGE_DIR@"
+ #define LLVM_TARGETS_BUILT "@LLVM_TARGETS_BUILT@"
+diff --git a/tools/llvm-config/llvm-config.cpp b/tools/llvm-config/llvm-config.cpp
+index e86eb2b44b10..f63e207e792e 100644
+--- a/tools/llvm-config/llvm-config.cpp
++++ b/tools/llvm-config/llvm-config.cpp
+@@ -366,7 +366,11 @@ int main(int argc, char **argv) {
+       sys::fs::make_absolute(ActivePrefix, Path);
+       ActiveBinDir = std::string(Path.str());
+     }
+-    ActiveLibDir = ActivePrefix + "/lib" + LLVM_LIBDIR_SUFFIX;
++    {
++      SmallString<256> Path(LLVM_INSTALL_LIBDIR LLVM_LIBDIR_SUFFIX);
++      sys::fs::make_absolute(ActivePrefix, Path);
++      ActiveLibDir = std::string(Path.str());
++    }
+     {
+       SmallString<256> Path(LLVM_INSTALL_PACKAGE_DIR);
+       sys::fs::make_absolute(ActivePrefix, Path);
diff --git a/pkgs/development/compilers/llvm/19/llvm/lit-shell-script-runner-set-dyld-library-path.patch b/pkgs/development/compilers/llvm/19/llvm/lit-shell-script-runner-set-dyld-library-path.patch
new file mode 100644
index 000000000000..e4f049f4b177
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/llvm/lit-shell-script-runner-set-dyld-library-path.patch
@@ -0,0 +1,12 @@
+--- a/utils/lit/lit/TestRunner.py	2024-03-15 17:27:53.170780798 -0700
++++ b/utils/lit/lit/TestRunner.py	2024-03-15 17:28:43.277447791 -0700
+@@ -1183,6 +1183,9 @@
+         f.write("@echo on\n")
+         f.write("\n@if %ERRORLEVEL% NEQ 0 EXIT\n".join(commands))
+     else:
++        if "DYLD_LIBRARY_PATH" in test.config.environment:
++            f.write(f'export DYLD_LIBRARY_PATH="{test.config.environment["DYLD_LIBRARY_PATH"]}"\n')
++
+         for i, ln in enumerate(commands):
+             match = re.fullmatch(kPdbgRegex, ln)
+             if match:
diff --git a/pkgs/development/compilers/llvm/19/llvm/llvm-lit-cfg-add-libs-to-dylib-path.patch b/pkgs/development/compilers/llvm/19/llvm/llvm-lit-cfg-add-libs-to-dylib-path.patch
new file mode 100644
index 000000000000..d4ccb2ae9822
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/llvm/llvm-lit-cfg-add-libs-to-dylib-path.patch
@@ -0,0 +1,80 @@
+diff --git a/test/Unit/lit.cfg.py b/test/Unit/lit.cfg.py
+index 81e8dc04acea..479ff95681e2 100644
+--- a/test/Unit/lit.cfg.py
++++ b/test/Unit/lit.cfg.py
+@@ -3,6 +3,7 @@
+ # Configuration file for the 'lit' test runner.
+ 
+ import os
++import platform
+ import subprocess
+ 
+ import lit.formats
+@@ -55,3 +56,26 @@ if sys.platform in ["win32", "cygwin"] and os.path.isdir(config.shlibdir):
+ # Win32 may use %SYSTEMDRIVE% during file system shell operations, so propogate.
+ if sys.platform == "win32" and "SYSTEMDRIVE" in os.environ:
+     config.environment["SYSTEMDRIVE"] = os.environ["SYSTEMDRIVE"]
++
++# Add the LLVM dynamic libs to the platform-specific loader search path env var:
++#
++# TODO: this is copied from `clang`'s `lit.cfg.py`; should unify..
++def find_shlibpath_var():
++    if platform.system() in ["Linux", "FreeBSD", "NetBSD", "OpenBSD", "SunOS"]:
++        yield "LD_LIBRARY_PATH"
++    elif platform.system() == "Darwin":
++        yield "DYLD_LIBRARY_PATH"
++    elif platform.system() == "Windows":
++        yield "PATH"
++    elif platform.system() == "AIX":
++        yield "LIBPATH"
++
++for shlibpath_var in find_shlibpath_var():
++    shlibpath = os.path.pathsep.join(
++        (config.shlibdir,
++         config.environment.get(shlibpath_var, '')))
++    config.environment[shlibpath_var] = shlibpath
++    break
++else:
++    lit_config.warning("unable to inject shared library path on '{}'"
++                       .format(platform.system()))
+diff --git a/test/lit.cfg.py b/test/lit.cfg.py
+index 75a38b4c5dad..856fc75c9d74 100644
+--- a/test/lit.cfg.py
++++ b/test/lit.cfg.py
+@@ -42,6 +42,26 @@ llvm_config.with_environment("PATH", config.llvm_tools_dir, append_path=True)
+ llvm_config.with_system_environment(
+     ["HOME", "INCLUDE", "LIB", "TMP", "TEMP"])
+ 
++# Add the LLVM dynamic libs to the platform-specific loader search path env var:
++#
++# TODO: this is copied from `clang`'s `lit.cfg.py`; should unify..
++def find_shlibpath_var():
++    if platform.system() in ["Linux", "FreeBSD", "NetBSD", "OpenBSD", "SunOS"]:
++        yield "LD_LIBRARY_PATH"
++    elif platform.system() == "Darwin":
++        yield "DYLD_LIBRARY_PATH"
++    elif platform.system() == "Windows":
++        yield "PATH"
++    elif platform.system() == "AIX":
++        yield "LIBPATH"
++
++for shlibpath_var in find_shlibpath_var():
++    shlibpath = config.llvm_shlib_dir
++    llvm_config.with_environment(shlibpath_var, shlibpath, append_path = True)
++    break
++else:
++    lit_config.warning("unable to inject shared library path on '{}'"
++                       .format(platform.system()))
+ 
+ # Set up OCAMLPATH to include newly built OCaml libraries.
+ top_ocaml_lib = os.path.join(config.llvm_lib_dir, "ocaml")
+@@ -318,7 +338,7 @@ def have_cxx_shared_library():
+ 
+     try:
+         readobj_cmd = subprocess.Popen(
+-            [readobj_exe, "--needed-libs", readobj_exe], stdout=subprocess.PIPE
++            [readobj_exe, "--needed-libs", readobj_exe], stdout=subprocess.PIPE, env=config.environment
+         )
+     except OSError:
+         print("could not exec llvm-readobj")
+
diff --git a/pkgs/development/compilers/llvm/19/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch b/pkgs/development/compilers/llvm/19/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch
new file mode 100644
index 000000000000..1354ad267314
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/llvm/polly-lit-cfg-add-libs-to-dylib-path.patch
@@ -0,0 +1,24 @@
+diff --git a/tools/polly/test/lit.cfg b/tools/polly/test/lit.cfg
+index 41e3a589c61e..09f3b17498b0 100644
+--- a/tools/polly/test/lit.cfg
++++ b/tools/polly/test/lit.cfg
+@@ -36,9 +36,17 @@ base_paths = [config.llvm_tools_dir, config.environment['PATH']]
+ path = os.path.pathsep.join(base_paths + config.extra_paths)
+ config.environment['PATH'] = path
+ 
++# (Copied from polly/test/Unit/lit.cfg)
++if platform.system() == 'Darwin':
++    shlibpath_var = 'DYLD_LIBRARY_PATH'
++elif platform.system() == 'Windows':
++    shlibpath_var = 'PATH'
++else:
++    shlibpath_var = 'LD_LIBRARY_PATH'
++
+ path = os.path.pathsep.join((config.llvm_libs_dir,
+-                              config.environment.get('LD_LIBRARY_PATH','')))
+-config.environment['LD_LIBRARY_PATH'] = path
++                              config.environment.get(shlibpath_var,'')))
++config.environment[shlibpath_var] = path
+ 
+ llvm_config.use_default_substitutions()
+ 
diff --git a/pkgs/development/compilers/llvm/19/openmp/fix-find-tool.patch b/pkgs/development/compilers/llvm/19/openmp/fix-find-tool.patch
new file mode 100644
index 000000000000..b7f51196f7ba
--- /dev/null
+++ b/pkgs/development/compilers/llvm/19/openmp/fix-find-tool.patch
@@ -0,0 +1,17 @@
+diff --git a/libomptarget/DeviceRTL/CMakeLists.txt b/libomptarget/DeviceRTL/CMakeLists.txt
+index 630947abec7e..9f032dc7bd3f 100644
+--- a/libomptarget/DeviceRTL/CMakeLists.txt
++++ b/libomptarget/DeviceRTL/CMakeLists.txt
+@@ -27,10 +27,10 @@ endif()
+ if (LLVM_DIR)
+   # Builds that use pre-installed LLVM have LLVM_DIR set.
+   # A standalone or LLVM_ENABLE_RUNTIMES=openmp build takes this route
+-  find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
++  find_program(CLANG_TOOL clang PATHS ${LLVM_TOOLS_BINARY_DIR})
+   find_program(PACKAGER_TOOL clang-offload-packager PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+   find_program(LINK_TOOL llvm-link PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+-  find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
++  find_program(OPT_TOOL opt PATHS ${LLVM_TOOLS_BINARY_DIR})
+   if ((NOT CLANG_TOOL) OR (NOT LINK_TOOL) OR (NOT OPT_TOOL) OR (NOT PACKAGER_TOOL))
+     libomptarget_say("Not building DeviceRTL. Missing clang: ${CLANG_TOOL}, llvm-link: ${LINK_TOOL}, opt: ${OPT_TOOL}, or clang-offload-packager: ${PACKAGER_TOOL}")
+     return()
diff --git a/pkgs/development/compilers/llvm/19/openmp/run-lit-directly.patch b/pkgs/development/compilers/llvm/19/openmp/run-lit-directly.patch
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/pkgs/development/compilers/llvm/default.nix b/pkgs/development/compilers/llvm/default.nix
index a4b8b548a0bd..eeab3a598cc0 100644
--- a/pkgs/development/compilers/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/default.nix
@@ -22,6 +22,7 @@ let
     "16.0.6".officialRelease.sha256 = "sha256-fspqSReX+VD+Nl/Cfq+tDcdPtnQPV1IRopNDfd5VtUs=";
     "17.0.6".officialRelease.sha256 = "sha256-8MEDLLhocshmxoEBRSKlJ/GzJ8nfuzQ8qn0X/vLA+ag=";
     "18.1.8".officialRelease.sha256 = "sha256-iiZKMRo/WxJaBXct9GdAcAT3cz9d9pnAcO1mmR6oPNE=";
+    "19.1.0-rc1".officialRelease.sha256 = "sha256-uaM+CKE+l+ksLtfhVMTLXbLlu+lUZScf+ucBcRENSDM=";
     "19.0.0-git".gitRelease = {
       rev = "d15ada24b1fbbd72776022383a5c557a1a056413";
       rev-version = "19.0.0-unstable-2024-07-21";
@@ -49,31 +50,28 @@ let
       attrName =
         args.name or (if (gitRelease != null) then "git" else lib.versions.major release_version);
     in
-    callPackage ./common {
-      inherit (stdenvAdapters) overrideCC;
-      buildLlvmTools = buildPackages."llvmPackages_${attrName}".tools;
-      targetLlvmLibraries =
-        targetPackages."llvmPackages_${attrName}".libraries or llvmPackages."${attrName}".libraries;
-      targetLlvm = targetPackages."llvmPackages_${attrName}".llvm or llvmPackages."${attrName}".llvm;
-      stdenv =
-        if (lib.versions.major release_version == "13" && stdenv.cc.cc.isGNU or false) then
-          gcc12Stdenv
-        else
-          stdenv; # does not build with gcc13
-      inherit bootBintoolsNoLibc bootBintools;
-      inherit
-        officialRelease
-        gitRelease
-        monorepoSrc
-        version
-        ;
-    };
+    lib.nameValuePair attrName (
+      callPackage ./common {
+        inherit (stdenvAdapters) overrideCC;
+        buildLlvmTools = buildPackages."llvmPackages_${attrName}".tools;
+        targetLlvmLibraries =
+          targetPackages."llvmPackages_${attrName}".libraries or llvmPackages."${attrName}".libraries;
+        targetLlvm = targetPackages."llvmPackages_${attrName}".llvm or llvmPackages."${attrName}".llvm;
+        stdenv =
+          if (lib.versions.major release_version == "13" && stdenv.cc.cc.isGNU or false) then
+            gcc12Stdenv
+          else
+            stdenv; # does not build with gcc13
+        inherit bootBintoolsNoLibc bootBintools;
+        inherit
+          officialRelease
+          gitRelease
+          monorepoSrc
+          version
+          ;
+      }
+    );
 
-  llvmPackages = lib.mapAttrs' (
-    version: args:
-    lib.nameValuePair (if (args ? gitRelease) then "git" else lib.versions.major version) (
-      mkPackage (args // { inherit version; })
-    )
-  ) versions;
+  llvmPackages = lib.mapAttrs' (version: args: mkPackage (args // { inherit version; })) versions;
 in
 llvmPackages
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index 7c55c361b0fb..797047833e74 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -15990,6 +15990,12 @@ with pkgs;
     lldb_18 = llvmPackages_18.lldb;
     llvm_18 = llvmPackages_18.llvm;
 
+    llvmPackages_19 = llvmPackagesSet."19";
+    clang_19 = llvmPackages_19.clang;
+    lld_19 = llvmPackages_19.lld;
+    lldb_19 = llvmPackages_19.lldb;
+    llvm_19 = llvmPackages_19.llvm;
+
     llvmPackages_git = llvmPackagesSet.git;
   }) llvmPackages_13
     llvmPackages_14
@@ -16001,6 +16007,11 @@ with pkgs;
     lld_18
     lldb_18
     llvm_18
+    llvmPackages_19
+    clang_19
+    lld_19
+    lldb_19
+    llvm_19
     llvmPackages_git;
 
   lorri = callPackage ../tools/misc/lorri {