riscv_dis_arch_priv_spec

Disassembler: Add overridable priv-spec and arch options

• Branch: riscv-dis-arch-priv-spec
• Tracking PR: #29 (view Pull Request and Diff)
• Mailing List:
  • PATCH v3 (2022-11-20) - binutils | gdb-patches

Requires

• Disassembler: Core reorganization for Optimization (Batch 1)

Based On

• Disassembler: Add arch disassembler option
  Version count is derived from this.
• Disassembler: Make ELF priv-spec overridable

Feature Description

(TODO)

Example

This is not hypothetical and even has a problem on ELF files.

OpenSBI is the prime example.

OpenSBI can be compiled with the current RISC-V GNU Toolchain (with privileged specification version 1.11) but uses hypervisor instructions. It also has ELF arch attribute "rv64i2p0_m2p0_a2p0_f2p0_d2p0_c2p0" (RV64GC with ISA version 2.2) if we compile for RV64 so there's no H-extension reference here.

An Excerpt from the Source Code (OpenSBI 1.1, lib/sbi/sbi_hfence.S):

    .align 3
    .global __sbi_hfence_gvma_vmid_gpa
__sbi_hfence_gvma_vmid_gpa:
    /*
    * rs1 = a0 (GPA >> 2)
    * rs2 = a1 (VMID)
    * HFENCE.GVMA a0, a1
    * 0110001 01011 01010 000 00000 1110011
    */
    .word 0x62b50073
    ret

• Target: fw_jump.elf from OpenSBI 1.1 (RV64)
• Compiler/Toolchain: RISC-V GNU Toolchain 2022.06.10

Before

• Command: riscv64-unknown-elf-objdump -d fw_jump.elf

00000000800097c8 <__sbi_hfence_gvma_vmid_gpa>:
    800097c8:  62b50073                .4byte  0x62b50073
    800097cc:  8082                    ret
    800097ce:  0001                    nop

After

• Command: riscv64-unknown-elf-objdump -M arch=rv64gch -d fw_jump.elf

00000000800097c8 <__sbi_hfence_gvma_vmid_gpa>:
    800097c8:  62b50073                hfence.gvma     a0,a1
    800097cc:  8082                    ret
    800097ce:  0001                    nop

Note

Even after this patchset, only 1 of 8 hfence.* instructions is correctly disassembled but the reason is separate: OpenSBI uses .word, not .insn (the disassembler handles some instructions emitted with .word as data). In this case, objdump -D may be a workaround.