The dyngen tool is the key of the QEMU translation process. The following tasks are carried out when running it on an object file containing micro operations:
• The object file is parsed to get its symbol table, its relocations entries and its code section. This pass depends on the host object file format (dyngen supports ELF (Linux), PE-COFF (Windows) and MACH-O (Mac OS X)).
• The micro operations are located in the code section using the symbol table. A host specific method is executed to get the start and the end of the copied code. Typically, the function prologue and epilogue are skipped.
• The relocations of each micro operations are examined to get the number of constant parameters. The constant parameter relocations are detected by the fact they use the specific symbol name op paramN.
• A memory copy in C is generated to copy the micro operation code. The relocations of the code of each micro operation are used to patch the copied code so that it is properly relocated. The relocation patches are host specific.
• （For some hosts such as ARM, constants must be stored near the generated code because they are accessed with PC relative loads with a small displacement. A host specific pass is done to relocate these constants in the generated code.）
When compiling the micro operation code, a set of GCC flags is used to manipulate the generation of function prologue and epilogue code into a form that is easy to parse. A dummy assembly macro forces GCC to always terminate the function corresponding to each micro operation with a single return instruction. Code concatenation would not work if several return instructions were generated in a single micro operation.
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