[PATCH] D124525: [OpenMP][ClangLinkerWrapper] Extending linker wrapper to embed metadata for multi-arch fat binaries

[Saiyedul Islam via Phabricator via cfe-commits]

saiislam added a comment.

In D124525#3478469 <https://reviews.llvm.org/D124525#3478469>, @yaxunl wrote:

> need a test for the generated registration code

Yes, I will add tests.



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Comment at: clang/tools/clang-linker-wrapper/ClangLinkerWrapper.cpp:1161
 
-    LinkedImages.push_back(*ImageOrErr);
+    LinkedImages.emplace_back(TheArch, *ImageOrErr);
   }
----------------
jhuber6 wrote:
> I'm doing something similar in D123810, I just used the existing `DeviceFile` because I needed the `Arch` and `Kind` fields to dispatch the appropriate wrapping job for CUDA / HIP.
Seems simpler. I will pull that change here.


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Comment at: clang/tools/clang-linker-wrapper/OffloadWrapper.cpp:98-104
+  // struct __tgt_image_info {
+  //   int32_t version;
+  //   int32_t image_number;
+  //   int32_t number_images;
+  //   char* offload_arch;
+  //   char* target_compile_opts;
+  // };
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yaxunl wrote:
> I am wondering whether we should add a few more fields to make it more generic for all offloading languages and platforms:
> 
> 
> ```
> char* target_triple;
> char* offloading_kind; // openmp, hip, etc
> char* file_type; // elf, spirv, bitcode, etc
> ```
Good idea. Though I am not sure whether file_type info is being propagated in by the linker-wrapper or not. I will check.


================
Comment at: clang/tools/clang-linker-wrapper/OffloadWrapper.cpp:246
   IRBuilder<> Builder(BasicBlock::Create(C, "entry", Func));
+  // Create calls to __tgt_register_image_info for each image
+  auto *NullPtr = llvm::ConstantPointerNull::get(Builder.getInt8PtrTy());
----------------
jhuber6 wrote:
> I'm wondering if it would be better to create a new `__tgt_bin_desc` and call a new `__tgt_register_lib` with it here so we don't need multiple calls here. Inside that new runtime function we could just widen or shrink the existing structs as needed. That way each device image would have this metadata associated with it and the target plugin can handle it as-needed.
Last time multiple vendors objected to changing `__tgt_bin_desc` and `__tgt_device_image` structs. The reason was backward compatibility of multiple downstream runtimes.


Repository:
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  https://reviews.llvm.org/D124525/new/

https://reviews.llvm.org/D124525