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RISC-V: Reorganize arch-related initialization and management
objdump reuses the disassembler function returned by the disassembler function. That's good and benefits well from various optimizations. However, by default, GDB (default_print_insn in gdb/arch-utils.c) assumes that the disassembler function logic is simple and calls that function for every instruction to be disassembled. This is clearly a waste of time because it probes BFD (ELF information) and re-initializes riscv_rps_dis for every instruction. After the support of mapping symbol with ISA string with commit 40f1a1a ("RISC-V: Output mapping symbols with ISA string."), this kind of per- instruction initialization of riscv_rps_dis can also occur on ELF files with mapping symbol + ISA string (in riscv_get_map_state function). It can be worse if the object is assembled using Binutils commit 0ce50fc ("RISC-V: Always generate mapping symbols at the start of the sections.") or later. To avoid repeated initialization, this commit - Caches the default / override architectures (in two "contexts") and - enables switching between them. riscv_dis_arch_context_t and new utility functions are defined for this purpose. We still have to read the ".riscv.attributes" section on every instruction on GDB but at least the most time-consuming part (updating the actual architecture from the architecture string) is avoided. Likewise, we still have to probe whether we have to update the architecture for every instruction with a mapping symbol with ISA string is suitable but at least we don't actually update the architecture unless necessary (either context itself or the ISA string of the current context is changed). This commit improves the disassembler performance well in those situations: - When long "disas" command is used on GDB - When ELF files with mapping symbols + ISA string is used This commit now implements new mapping symbol handling ("$x" means revert to the previous architecture [with "$x+arch"] if exists, otherwise revert to the default one usually read from an ELF attribute), the recent consensus made by Kito and Nelson. On the benchmark using GDB batch files, the author measured significant performance improvements (35-96% on various big RISC-V programs). Unfortunately, on interactive usecases of GDB, this improvement is rarely observable since we don't usually disassemble such a big chunk at once and the current disassembler is not very slow. On the benchmark using unstripped ELF files with mapping symbols + ISA string "$xrv...", performance improvements are significant and easily observable in the real world (150%-264% performance improvments). Aside from optimization, this commit, along with "RISC-V: Reorganize disassembler state initialization", makes state initialization clearer and makes further changes easier. Also, although not practical in the real world, this commit now allows multi-XLEN object disassembling if the object file has mapping symbols with ISA string and the machine is XLEN-neutral (e.g. objdump with "-m riscv" option). It may help testing Binutils / GAS. opcodes/ChangeLog: * riscv-dis.c (initial_default_arch): Special default architecture string which is handled separately. (riscv_subsets): Remove as it is replaced to a member of the disassembler context. (riscv_dis_arch_context_t): New type to manage RISC-V architecture context for the disassembler. Two instance of this type is defined in this file - "default" and "override". (dis_arch_context_default): New. Architecture context inferred from either an ELF attribute or initial_default_arch. (dis_arch_context_override): New. Architecture context inferred from mapping symbols with ISA string. (dis_arch_context_current): New. A pointer to either dis_arch_context_default or dis_arch_context_override. (riscv_rps_dis): Add summary. Use initial values from dis_arch_context_default. (from_last_map_symbol): Make it file scope to decide whether we should revert the architecture to the default in riscv_get_map_state function. (set_riscv_current_dis_arch_context): New function to update riscv_rps_dis and dis_arch_context_current. (set_riscv_dis_arch_context): New function to update the architecture for the given context. (free_riscv_dis_arch_context): New function to free memory. (update_riscv_dis_xlen): Consider dis_arch_context_current->xlen when guessing correct XLEN. (is_arch_changed): New. Set to true if the architecture is changed. (init_riscv_dis_state_for_arch): New function to track whether the architecture string is changed. (init_riscv_dis_state_for_arch_and_options): Keep track of the architecture string change and update XLEN if it has changed. (update_riscv_dis_arch): New function to set both the architecture and the context. Call initialization functions if needed. (riscv_get_map_state): Add update argument. Keep track of the mapping symbols with ISA string and update the architecture and the context if required. (riscv_search_mapping_symbol): Move from_last_map_symbol to file scope. Call riscv_get_map_state function with architecture and context updates enabled. (riscv_data_length): Call riscv_get_map_state function with architecture and context updates disabled. (riscv_get_disassembler): Add an error handling on Tag_RISCV_arch. Call update_riscv_dis_arch function to update the architecture and the context. (disassemble_free_riscv) Free disassembler context memory. Co-developed-by: Nelson Chu <[email protected]>
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