[llvm-dev] llvm-objdump cannot recognize mul&mulh RISC-V M Instructions

[Simon Cook via llvm-dev]

Hi,

Unlike GNU objdump, llvm-objdump doesn't assume that for RISC-V all
standard extensions are available by default, and so need to be
provided on the command line. I'm not aware of a flag that you can
pass a RISC-V ISA string to (from your command it seems --arch doesn't
do this for you), but you can enable the disassembly of instructions
using the underlying attributes and the --mattr flag, so in your case
adding `--mattr=+m` to your llvm-objdump command (I think `--mattr=m`
should work as well).

Hope this helps.

Thanks,
Simon

On Fri, Mar 27, 2020 at 9:23 AM Junning Wu via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> I am using llvm-project compiling risc-v programs.
>
> llvm-project version:dd8a2013dc1804be1b7d9cffacad2e984300bd22
>
> Instructons to build LLVM+clang:
>
> ```
> cmake -G Ninja -DCMAKE_INSTALL_PREFIX=/home/llvm/workspace/llvm/llvm-project/llvm_install -DCMAKE_BUILD_TYPE="Release" -DDEFAULT_SYSROOT="/home/llvm/workspace/riscv/riscv-tc-20200220/bin/riscv32-unknown-elf" -DGCC_INSTALL_PREFIX="/home/llvm/workspace/riscv/riscv-tc-20200220" -DLLVM_DEFAULT_TARGET_TRIPLE="riscv32-unknown-elf" -DLLVM_ENABLE_PROJECTS="clang;lld;libc" -DLLVM_TARGETS_TO_BUILD="RISCV" ../llvm
> ```
>
> Instructions to compile and dump:
>
> ```
> RISCV_GCC_OPTS ?= -mcmodel=medany -static -O3 -std=gnu99 -fno-common -fno-builtin -march=rv32im -mabi=ilp32 -DMB_ADDR=0x80FFFFC --target=riscv64-unknown-elf --sysroot=/home/llvm/workspace/riscv/riscv-tc-20200220/bin/riscv64-unknown-elf --gcc-toolchain=/home/llvm/workspace/riscv/riscv-tc-20200220
> RISCV_LINK_OPTS ?= -static -nostdlib -nostartfiles -lm -lgcc -T /home/llvm/workspace/HRV_IDE/common/test.ld
> newlib_dir := /home/llvm/workspace/llvm/llvm-project/llvm_install/riscv64-unknown-elf/include
> src_dir := $(WORK_DIR)/src/$(PROJ)
> incs  += -I$(WORK_DIR)/env -I$(WORK_DIR)/common -I$(src_dir) -I$(newlib_dir)
> src := $(wildcard $(src_dir)/*.c) $(wildcard $(WORK_DIR)/common/*.c) $(wildcard $(WORK_DIR)/common/*.S)
>
> $(RISCV_clang) $(incs) $(RISCV_GCC_OPTS) -o $(WORK_DIR)/build/$@/$@ $(src) $(RISCV_LINK_OPTS) --verbose
> $(RISCV_OBJDUMP) -d $(WORK_DIR)/build/$@/$@ > $(WORK_DIR)/build/$@/$@.S
> $(RISCV_LLVM_OBJDUMP) --arch=rv32imac -D $(WORK_DIR)/build/$@/$@ > $(WORK_DIR)/build/$@/$@.ASM
> ```
> gcc objdump result:
> ```
> 4001168: 00052383           lw t2,0(a0)
>  400116c: 979a                 add a5,a5,t1
>  400116e: 439c                 lw a5,0(a5)
>  4001170: 0308a533           mulhsu a0,a7,a6
> ```
>
> llvm-objdump result:
>
> ```
>  4001168: 83 23 05 00                   lw t2, 0(a0)
>  400116c: 9a 97                         add a5, a5, t1
>  400116e: 9c 43                         lw a5, 0(a5)
>  4001170: 33 a5 08 03                   <unknown>
> ```
>
> Does anyone knows what is the problem and how to fix it?
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