Compile a C file with Zce ext in LLVM

update details 展开目录

1. update branch of LLVM
2. change -march from rv64imaczca0p50 into rv64imaczce0p50
3. How to compile with Zce compile switchs.
4. Specify the arch/abi as rv64imac/lp64 when build gnu toolchain. because default is rv64imafdc/lp64d
5. motify c files

Compile a C file with Zce ext in LLVM 展开目录

In this article, we try to compile a C program in LLVM using RISCV architecture and Zce Extension.

The files mentioned in the article are in follow links Materials

Build GNU tool chain 展开目录

Looking riscv-gnu-toolchain repo for more information

git clone https://github.com/riscv/riscv-gnu-toolchain
cd riscv-gnu-toolchain
./configure --prefix=$HOME/opt/riscv --enable-multilib --with-arch=rv64imac --with-abi=lp64
make # Newlib

Export the Env path for GNU tool chain

export PATH=$HOME/opt/riscv/bin:$PATH

Build LLVM 展开目录

# clone the source code of LLVM
git clone -b riscv-zce-llvm14 https://github.com/plctlab/llvm-project.git
cd llvm-project/
mkdir build
cd build
cmake -DLLVM_TARGETS_TO_BUILD="RISCV" -DLLVM_ENABLE_PROJECTS="clang;lld;libcxx;libcxxabi" -G "Unix Makefiles"  ../llvm
make -j

• -DCMAKE_BUILD_TYPE=type — Valid options for type are Debug, Release, RelWithDebInfo, and MinSizeRel. Default is Debug.

  Note: release builds are 2.2gb while debug builds are 15gb

import the PATH 展开目录

export PATH=$HOME/llvm-project/build/bin:$PATH

Compile C program 展开目录

Write C file 展开目录

Write code into hello.c

int test(){
    int c = 63;
    int a = 6;
    int b = a * c * 30;
    return b;
}

#include<stdio.h>
const int GLOAL_ZCE = 1;
int fbm(int a, int b, int count){
    int res = a * b;
    printf("a --> %d, b --> %d\n", a, b);
    printf("result is %d\n", res);
    if(count>1)
        return fbm(b,res,count-1);
    else
        return res;
}

int main(int argc, char const *argv[])
{
    char x=-1;
    printf("%d\n",  x);
    int a = 1;
    int b = 2;
    int result = fbm(a,b,7) + test();
    return 0;
}

Compile 展开目录

Than compile source code by following command

clang --target=riscv64 -march=rv64imaczce0p50 -menable-experimental-extensions --gcc-toolchain=$HOME/opt/riscv -o hello.o hello.c
# or
clang --target=riscv64 -march=rv64imaczce0p50 -menable-experimental-extensions --gcc-toolchain=$HOME/opt/riscv -fuse-ld=lld -mno-relax -o hello.o hello.c

the second command is use lld as linker

some instructions of Zce require M ext

We use gnu tool chain here. The parameter --gcc-toolchain should be the path of GNU tool chain you have just build.

Dump the Obj file 展开目录

llvm-objdump --mattr=+experimental-zce,+m,+c -d -r hello.o

For param --mattr, we'd better keep it same as which do we used in compiling.

We can find the c.mul has been been used.

Compile with switchs 展开目录

we also implement the compile switchs so that you can use only specific instructions of Zce Ext to compile or evaluate.

e.g. compile with only MULI, use following command

clang --target=riscv64 -march=rv64imac -mzce-muli -gcc-toolchain=$HOME/opt/riscv -o hello.o hello.c
# or
clang --target=riscv64 -march=rv64imac -mzce-muli --gcc-toolchain=$HOME/opt/riscv -fuse-ld=lld -mno-relax -o hello.o hello.c

Then Dump Obj file again, we find the muli while c.mul disappears.

Run on Qemu 展开目录

Build Qemu 展开目录

git clone -b plct-zce-dev https://github.com/plctlab/plct-qemu.git
cd plct-qemu
./configure --target-list=riscv64-linux-user
make

import the PATH 展开目录

export PATH=$HOME/report/plct-qemu/build:$PATH

Run on qemu 展开目录

qemu-riscv64 -cpu rv64,x-zce=true hello.o

You can comment below or email me if you have any issues.