[Module] Implement custom imported modules serialization #15666
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When a module with imported modules is exported into a shared library, the imported modules are serialized and embedded inside of that library. This is done by generating a raw binary from the imported modules, which is then assigned to a symbol `__tvm_dev_mblob` in the final shared library. The way it happens for targets that are not "llvm", is by creating a C source file, and defining a statically-initialized array `__tvm_dev_mblob` in it. The static initializer is the byte-by-byte hexadecimal represen- tation of the serialized modules. While working with Hexagon, this has presented us with two issues: 1. For most models, the embedded data is very large, taking significant amout of time to compile the auto-generated C source. 2. There are some models for which the C source size has exceeded clang's limits on the size of the input file, making it impossible to export the corresponding module. This PR allows users to provide a custom serialization routine to `Module.export_library`. We then apply it in Hexagon to build the ELF object file with `__tvm_dev_mblob` by using the objcopy tool from the Hexagon toolchain. This bypasses the C compilation altogether, avoiding both of the issues. Using the same custom mechanism, similar method can be implemented for many other targets which have utilities to manipulate object files directly.
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It seems like older toolchains may work as well, but the oldest supported SDK is 4.5.0.3, which contains toolchain version 8.5.08.
tqchen
approved these changes
Sep 6, 2023
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When a module with imported modules is exported into a shared library, the imported modules are serialized and embedded inside of that library. This is done by generating a raw binary from the imported modules, which is then assigned to a symbol
__tvm_dev_mblobin the final shared library.The way it happens for targets that are not "llvm", is by creating a C source file, and defining a statically-initialized array
__tvm_dev_mblobin it. The static initializer is the byte-by-byte hexadecimal representation of the serialized modules. While working with Hexagon, this has presented us with two issues:This PR allows users to provide a custom serialization routine to
Module.export_library. We then apply it in Hexagon to build the ELF object file with__tvm_dev_mblobby using the objcopy tool from the Hexagon toolchain. This bypasses the C compilation altogether, avoiding both of the issues.Using the same custom mechanism, similar method can be implemented for many other targets which have utilities to manipulate object files directly.