Re: Kernel functions showing only addresses in `perf` output

[Namhyung Kim <namhyung@kernel.org>]

Hello,

On Wed, Jul 24, 2024 at 07:11:27PM +0800, 吴雨薇 wrote:
> Kernel functions are only showing addresses and not symbols in the sampling output from the `perf` tool.
> 
> Environment Information
> - Hardware: SG2042
> - OS Version: openEuler 23.09
> - Kernel Version: Linux openeuler-riscv64 6.6.0+ #1 SMP Wed Apr 3 15:53:06 CST 2024 riscv64 riscv64 riscv64 GNU/Linux
> - Perf Version: 6.6.g04f0a6491967
> - Kernel Compilation Options:
> The following kernel configuration options have been enabled:
> CONFIG_PERF_EVENTS
> CONFIG_KALLSYMS
> CONFIG_KALLSYMS_ALL
> CONFIG_FRAME_POINTER
> CONFIG_STACKTRACE
> CONFIG_DEBUG_INFO
> 
> CONFIG_DEBUG_KERNEL
> 
> 
> 
> Steps to Reproduce
> 
> 1. Download Kernel Source Code:
>    Clone the kernel source code repository on the Lichee Pi 4A board
> 
> 2. Install Dependencies:
>    Install all necessary development libraries and tools required by `perf`:
>    sudo yum install elfutils-libelf-devel -y
>    sudo yum install perl-devel -y
>    sudo yum install numactl-devel -y
>    sudo yum install libbabeltrace-devel -y
>    sudo yum install binutils-devel -y
>    sudo yum install genwqe-zlib-static -y
>    sudo yum install elfutils-devel -y
>    sudo yum install slang-devel -y
>    sudo yum install zstd-devel -y
>    sudo yum install xz-devel -y
>    sudo yum install libcap-devel -y
>    sudo yum install audit-devel audit-libs -y
>    sudo yum install openssl-devel -y
>    sudo yum install gtk2-devel -y
>    sudo yum install systemtap-sdt-devel -y
>    sudo yum install libtraceevent-devel -y
>    sudo yum install libpfm -y
>    sudo yum install ncurses-devel -y
>    sudo yum install java-1.8.0-openjdk-devel -y
> 
> 3. Compile `perf`:
>    cd riscv-kernel/tools/perf
>    make ARCH=riscv WERROR=0 -j4
> 
> 4. Install `perf`:
>    sudo cp ./perf /usr/bin/
> 
> 5. Download `hackbench`
> 
> 6. Compile `hackbench`:
>    gcc -static -O0 -g -fno-omit-frame-pointer hackbench.c -o hackbench -lpthread
> 
> 7. Run Tests with `perf`:
>    Record performance data with `perf` and generate the report:
>    sudo perf record -e cpu-cycles -g ./hackbench
>    sudo perf report --no-children -G > perf_hackbench.txt
> 
> 
> Issue
> In the `perf_hackbench.txt` output, you can see that kernel functions show addresses, while user mode functions show function symbol names
> 96.22%  hackbench  [unknown]          [k] 0xffffffff80cfb2ac
> 
> Potential Cause：
> It seems that `perf` might be failing to resolve addresses to symbols because it cannot find the addresses in `/proc/kallsyms`.

Can you please run `perf script --show-mmap-events` ?
I'd like to see if it has proper mappings in the data file.

Thanks,
Namhyung