From 89d50591c06f084b80a5ce527781e07f8dc32be6 Mon Sep 17 00:00:00 2001 From: Manuel Drehwald Date: Fri, 21 Nov 2025 00:14:03 -0800 Subject: [PATCH 1/2] Replace the first of 4 binary invocations for offload --- compiler/rustc_codegen_llvm/src/back/write.rs | 7 +++ compiler/rustc_codegen_llvm/src/llvm/ffi.rs | 3 ++ .../rustc_llvm/llvm-wrapper/RustWrapper.cpp | 47 +++++++++++++++++++ 3 files changed, 57 insertions(+) diff --git a/compiler/rustc_codegen_llvm/src/back/write.rs b/compiler/rustc_codegen_llvm/src/back/write.rs index fde7dd6ef7a85..78b11c458d5aa 100644 --- a/compiler/rustc_codegen_llvm/src/back/write.rs +++ b/compiler/rustc_codegen_llvm/src/back/write.rs @@ -765,6 +765,13 @@ pub(crate) unsafe fn llvm_optimize( llvm_plugins.len(), ) }; + + if cgcx.target_is_like_gpu && config.offload.contains(&config::Offload::Enable) { + unsafe { + llvm::LLVMRustBundleImages(module.module_llvm.llmod(), module.module_llvm.tm.raw()); + } + } + result.into_result().unwrap_or_else(|()| llvm_err(dcx, LlvmError::RunLlvmPasses)) } diff --git a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs index ca64d96c2a33c..34f0e4b953381 100644 --- a/compiler/rustc_codegen_llvm/src/llvm/ffi.rs +++ b/compiler/rustc_codegen_llvm/src/llvm/ffi.rs @@ -1641,6 +1641,9 @@ unsafe extern "C" { Name: *const c_char, ) -> &'a Value; + /// Processes the module and writes it in an offload compatible way into a "host.out" file. + pub(crate) fn LLVMRustBundleImages<'a>(M: &'a Module, TM: &'a TargetMachine) -> bool; + /// Writes a module to the specified path. Returns 0 on success. pub(crate) fn LLVMWriteBitcodeToFile(M: &Module, Path: *const c_char) -> c_int; diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp index 8823c83922822..ba17aef92d0d5 100644 --- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp +++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp @@ -25,6 +25,7 @@ #include "llvm/IR/Module.h" #include "llvm/IR/Value.h" #include "llvm/Object/COFFImportFile.h" +#include "llvm/Object/OffloadBinary.h" #include "llvm/Remarks/RemarkFormat.h" #include "llvm/Remarks/RemarkSerializer.h" #include "llvm/Remarks/RemarkStreamer.h" @@ -35,6 +36,7 @@ #include "llvm/Support/Signals.h" #include "llvm/Support/Timer.h" #include "llvm/Support/ToolOutputFile.h" +#include "llvm/Target/TargetMachine.h" #include "llvm/Transforms/Utils/Cloning.h" #include "llvm/Transforms/Utils/ValueMapper.h" #include @@ -144,6 +146,51 @@ extern "C" void LLVMRustPrintStatistics(RustStringRef OutBuf) { llvm::PrintStatistics(OS); } +static Error writeFile(StringRef Filename, StringRef Data) { + Expected> OutputOrErr = + FileOutputBuffer::create(Filename, Data.size()); + if (!OutputOrErr) + return OutputOrErr.takeError(); + std::unique_ptr Output = std::move(*OutputOrErr); + llvm::copy(Data, Output->getBufferStart()); + if (Error E = Output->commit()) + return E; + return Error::success(); +} + +// This is the first of many steps in creating a binary using llvm offload, +// to run code on the gpu. Concrete, it replaces the following binary use: +// clang-offload-packager -o host.out +// --image=file=device.bc,triple=amdgcn-amd-amdhsa,arch=gfx90a,kind=openmp +// The input module is the rust code compiled for a gpu target like amdgpu. +// Based on clang/tools/clang-offload-packager/ClangOffloadPackager.cpp +extern "C" bool LLVMRustBundleImages(LLVMModuleRef M, TargetMachine &TM) { + std::string Storage; + llvm::raw_string_ostream OS1(Storage); + llvm::WriteBitcodeToFile(*unwrap(M), OS1); + OS1.flush(); + auto MB = llvm::MemoryBuffer::getMemBufferCopy(Storage, "module.bc"); + + SmallVector BinaryData; + raw_svector_ostream OS2(BinaryData); + + OffloadBinary::OffloadingImage ImageBinary{}; + ImageBinary.TheImageKind = object::IMG_Bitcode; + ImageBinary.Image = std::move(MB); + ImageBinary.TheOffloadKind = object::OFK_OpenMP; + ImageBinary.StringData["triple"] = TM.getTargetTriple().str(); + ImageBinary.StringData["arch"] = TM.getTargetCPU(); + llvm::SmallString<0> Buffer = OffloadBinary::write(ImageBinary); + if (Buffer.size() % OffloadBinary::getAlignment() != 0) + // Offload binary has invalid size alignment + return false; + OS2 << Buffer; + if (Error E = writeFile("host.out", + StringRef(BinaryData.begin(), BinaryData.size()))) + return false; + return true; +} + extern "C" void LLVMRustOffloadMapper(LLVMValueRef OldFn, LLVMValueRef NewFn) { llvm::Function *oldFn = llvm::unwrap(OldFn); llvm::Function *newFn = llvm::unwrap(NewFn); From 88ca3bc7322d8b0c8738da0dec9bc2f5502d2643 Mon Sep 17 00:00:00 2001 From: Manuel Drehwald Date: Fri, 21 Nov 2025 01:47:47 -0800 Subject: [PATCH 2/2] update dev guide --- src/doc/rustc-dev-guide/src/offload/usage.md | 14 ++------------ 1 file changed, 2 insertions(+), 12 deletions(-) diff --git a/src/doc/rustc-dev-guide/src/offload/usage.md b/src/doc/rustc-dev-guide/src/offload/usage.md index 7abf90aa6e0b6..8350fb5777fba 100644 --- a/src/doc/rustc-dev-guide/src/offload/usage.md +++ b/src/doc/rustc-dev-guide/src/offload/usage.md @@ -79,19 +79,8 @@ Now we generate the device code. Replace the target-cpu with the right code for RUSTFLAGS="-Ctarget-cpu=gfx90a --emit=llvm-bc,llvm-ir -Zoffload=Enable -Zunstable-options" cargo +offload build -Zunstable-options -r -v --target amdgcn-amd-amdhsa -Zbuild-std=core ``` -Now find the `.ll` under target/amdgcn-amd-amdhsa folder and copy it to a device.ll file (or adjust the file names below). -If you work on an NVIDIA or Intel gpu, please adjust the names acordingly and open an issue to share your results (either if you succeed or fail). -First we compile our .ll files (good for manual inspections) to .bc files and clean up leftover artifacts. The cleanup is important, otherwise caching might interfere on following runs. -``` -opt lib.ll -o lib.bc -opt device.ll -o device.bc -rm *.o -rm bare.amdgcn.gfx90a.img* -``` ``` -"clang-offload-packager" "-o" "host.out" "--image=file=device.bc,triple=amdgcn-amd-amdhsa,arch=gfx90a,kind=openmp" - "clang-21" "-cc1" "-triple" "x86_64-unknown-linux-gnu" "-S" "-save-temps=cwd" "-disable-free" "-clear-ast-before-backend" "-main-file-name" "lib.rs" "-mrelocation-model" "pic" "-pic-level" "2" "-pic-is-pie" "-mframe-pointer=all" "-fmath-errno" "-ffp-contract=on" "-fno-rounding-math" "-mconstructor-aliases" "-funwind-tables=2" "-target-cpu" "x86-64" "-tune-cpu" "generic" "-resource-dir" "//rust/build/x86_64-unknown-linux-gnu/llvm/lib/clang/21" "-ferror-limit" "19" "-fopenmp" "-fopenmp-offload-mandatory" "-fgnuc-version=4.2.1" "-fskip-odr-check-in-gmf" "-fembed-offload-object=host.out" "-fopenmp-targets=amdgcn-amd-amdhsa" "-faddrsig" "-D__GCC_HAVE_DWARF2_CFI_ASM=1" "-o" "host.s" "-x" "ir" "lib.bc" "clang-21" "-cc1as" "-triple" "x86_64-unknown-linux-gnu" "-filetype" "obj" "-main-file-name" "lib.rs" "-target-cpu" "x86-64" "-mrelocation-model" "pic" "-o" "host.o" "host.s" @@ -99,7 +88,8 @@ rm bare.amdgcn.gfx90a.img* "clang-linker-wrapper" "--should-extract=gfx90a" "--device-compiler=amdgcn-amd-amdhsa=-g" "--device-compiler=amdgcn-amd-amdhsa=-save-temps=cwd" "--device-linker=amdgcn-amd-amdhsa=-lompdevice" "--host-triple=x86_64-unknown-linux-gnu" "--save-temps" "--linker-path=/ABSOlUTE_PATH_TO/rust/build/x86_64-unknown-linux-gnu/lld/bin/ld.lld" "--hash-style=gnu" "--eh-frame-hdr" "-m" "elf_x86_64" "-pie" "-dynamic-linker" "/lib64/ld-linux-x86-64.so.2" "-o" "bare" "/lib/../lib64/Scrt1.o" "/lib/../lib64/crti.o" "/ABSOLUTE_PATH_TO/crtbeginS.o" "-L/ABSOLUTE_PATH_TO/rust/build/x86_64-unknown-linux-gnu/llvm/bin/../lib/x86_64-unknown-linux-gnu" "-L/ABSOLUTE_PATH_TO/rust/build/x86_64-unknown-linux-gnu/llvm/lib/clang/21/lib/x86_64-unknown-linux-gnu" "-L/lib/../lib64" "-L/usr/lib64" "-L/lib" "-L/usr/lib" "host.o" "-lstdc++" "-lm" "-lomp" "-lomptarget" "-L/ABSOLUTE_PATH_TO/rust/build/x86_64-unknown-linux-gnu/llvm/lib" "-lgcc_s" "-lgcc" "-lpthread" "-lc" "-lgcc_s" "-lgcc" "/ABSOLUTE_PATH_TO/crtendS.o" "/lib/../lib64/crtn.o" ``` -Especially for the last command I recommend to not fix the paths, but rather just re-generate them by copying a bare-mode openmp example and compiling it with your clang. By adding `-###` to your clang invocation, you can see the invidual steps. +Especially for the last three commands I recommend to not fix the paths, but rather just re-generate them by copying a bare-mode openmp example and compiling it with your clang. By adding `-###` to your clang invocation, you can see the invidual steps. +You can ignore other steps, e.g. the invocation of a "clang-offload-packager". ``` myclang++ -fuse-ld=lld -O3 -fopenmp -fopenmp-offload-mandatory --offload-arch=gfx90a omp_bare.cpp -o main -### ```