How can I get perf to find symbols in my program

Question

When using perf report, I don't see any symbols for my program, instead I get output like this:

$ perf record /path/to/racket ints.rkt 10000
$ perf report --stdio

# Overhead   Command      Shared Object  Symbol
# ........  ........  .................  ......
#
    70.06%  ints.rkt  [unknown]          [.] 0x5f99b8        
    26.28%  ints.rkt  [kernel.kallsyms]  [k] 0xffffffff8103d0ca
     3.66%  ints.rkt  perf-32046.map     [.] 0x7f1d9be46650  

Which is fairly uninformative.

The relevant program is built with debugging symbols, and the sysprof tool shows the appropriate symbols, as does Zoom, which I think is using perf under the hood.

Note that this is on x86-64, so the binary is compiled with -fomit-frame-pointer, but that's the case when running under the other tools as well.

Solution 1

This post is already over a year old, but since it came out at the top of my Google search results when I had the same problem, I thought I'd answer it here. After some more searching around, I found the answer given in this related StackOverflow question very helpful. On my Ubuntu Raring system, I then ended up doing the following:

1. Compile my C++ sources with -g (fairly obvious, you need debug symbols)

2. Run perf as

   record -g dwarf -F 97 /path/to/my/program
   

   This way perf is able to handle the DWARF 2 debug format, which is the standard format gcc uses on Linux. The -F 97 parameter reduces the sampling rate to 97 Hz. The default sampling rate was apparently too large for my system and resulted in messages like this:

   Warning:
   Processed 172390 events and lost 126 chunks!
   
   Check IO/CPU overload!
   

   and the perf report call afterwards would fail with a segmentation fault. With the reduced sampling rate everything worked out fine.

3. Once the perf.data file has been generated without any errors in the previous step, you can run perf report etc. I personally like the FlameGraph tools to generate SVG visualizations.

4. Other people reported that running

   echo 0 > /proc/sys/kernel/kptr_restrict
   

   as root can help as well, if kernel symbols are required.

Solution 2

In my case the solution was to delete the elf files which contained cached symbols from previous builds and were messing things up.

They are in ~/.debug/ folder

Solution 3

You can always use the '$ nm ' command.

here is some sample output:

Ethans-MacBook-Pro:~ phyrrus9$ nm a.out
0000000100000000 T __mh_execute_header
0000000100000f30 T _main
                 U _printf
0000000100000f00 T _sigint
                 U _signal
                 U dyld_stub_binder

Solution 4

Make sure that you compile the program using -g option along with gcc(cc) so that debugging information is produced in the operating system's native format. Try to do the following and check if there are debug symbols present in the symbol table.

$objdump -t your-elf 
$readelf -a your-elf
$nm -a your-elf

Solution 5

I had this problem too, I couldn't see any userspace symbol, but I saw some kernel symbols. I thought this was a symbol loading issue. After tried all the possible solutions I could find, I still couldn't get it work.

Then I faintly remember that

ulimit -u unlimited

is needed. I tried and it magically worked.

I found from this wiki that this command is needed when you use too many file descriptors.

https://perf.wiki.kernel.org/index.php/Tutorial#Troubleshooting_and_Tips

my final command was

perf record -F 999 -g ./my_program

didn't need --call-graph

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