A deep dive into QEMU: The Tiny Code Generator (TCG), part 1
9 days ago
- #TCG
- #Virtualization
- #QEMU
- The blog post explains the internals of QEMU's TCG engine, which translates and executes target instructions on the host.
- The process involves generating intermediate representation (IR) code and then converting it into host architecture assembly instructions.
- The TCG engine uses frontend operations for generated intermediate code and backend operations for host CPU execution.
- The `gen_intermediate_code` function is architecture-dependent and wraps the generic `translator_loop` function.
- The `translator_loop` relies on target-specific translator operators, such as those for PowerPC (`ppc_tr_ops`).
- Translation Blocks (TBs) have prologues (`tb_start`) and epilogues (`tb_end`), which include generic and target-specific parts.
- The `DisasContext` is created alongside a generic `DisasContextBase` to record CPU state information.
- The `gen_tb_start` function injects instructions to check for instruction count and exit conditions.
- The `gen_tb_end` function injects instructions to exit from the TB, using `tcg_gen_exit_tb`.
- The `translate_insn` operator converts target instructions to IR, using the target CPU's opcodes handlers table.
- The post provides an example of PowerPC instructions (`cmp`, `stw`, `mtmsr`) and their TCG IR equivalents.
- Memory write operations and MSR accesses are translated into specific IR opcodes, which will be detailed in a future post.