Unable to profile program with clang-9 and libc++ with VTune

[Marshall__Andrew]

Steps to reproduce - 

compile the following program:

#include <iostream>

int main() {
    std::cout << "Hello World" << std::endl;
    return 0;
}

with

clang++-9 hello_world.cpp --stdlib=libc++  -g -O2 -o hello_world.exe

Attempting to profile with VTune results in the following error

Source/pin/elfio/img_elf.cpp: ProcessSectionHeaders: 809: unknown section type 0x6fff4c04 for sec[124,.deplibs] in /usr/lib/x86_64-linux-gnu    /libc++.so.1

# Product Version

Intel VTune Profile 2020 Update 1

Product Build 607630

# System info:

Collection and Platform Info
    Application Command Line:    /home/andrew/projects/fuel3d/work/hello_world.exe 
    Operating System:    5.3.0-53-generic NAME="Ubuntu"

VERSION="18.04.4 LTS (Bionic Beaver)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 18.04.4 LTS"
VERSION_ID="18.04"

    CPU
        Name:    Intel(R) microarchitecture code named Coffeelake
        Frequency:    3.6 GHz 
        Logical CPU Count:    16
 

[Vladimir_R_Intel]

Hi Andrew,

thank you for notification. According to the error message all VTune analyses using User Mode sampling or Tracing technology are broken, we will try to fix this in the nearest time. 

As a workaround I suggest to use HW based sampling analyses.

BR,

Vladimir

[JananiC_Intel]

Hi,

Thanks for reaching out.

We tried from our side and we experienced similar issue.As Vladimir said,our engineering team will fix this issue.Meanwhile you can try hardware sampling using the below command

vtune -collect hotspots -knob sampling-mode=hw -knob sampling-interval=1 -- ./hello_world.exe

We tried the above command it is working fine.

[Marshall__Andrew]

Thanks,

Regarding hardware sampling, the documentation could do with some additional information on installing the drivers on a system with Secure-Boot enabled, as is fairly common on a modern system.

All the kernel modules need to be signed with kmodsign in order to load. Just a link to https://ubuntu.com/blog/how-to-sign-things-for-secure-boot would be helpful.

[JananiC_Intel]

Hi,

We tried User mode sampling from our side ,now it seems to be working.Could you try that once again and let us know?

[Osnat_L_Intel]

Hi Marshall,

Can you please send me the binary that caused the error (libc++.so.1) ?

Even better to send a tar file with the executable and all its dependent libraries.

Thanks

Osnat

[AckoftOvak]

I have the same issue. Here is the binary.

[JananiC_Intel]

Hi,

Could you provide an update to Osnat Levi's query?

[JananiC_Intel]

Hi,

We are closing the case.Please raise a new thread in case of any further issues. 

Thanks.

[Bernard]

Source/pin/elfio/img_elf.cpp: ProcessSectionHeaders: 809: unknown section type 0x6fff4c04 for sec[124,.deplibs] in /usr/lib/x86_64-linux-gnu    /libc++.so.1

Looks like failure to parse and process some ELF64 section.

Maybe this could have affected the mapping of counter overflow to specific code trigger.

[AckoftOvak]

> Looks like failure to parse and process some ELF64 section.

It's SHT_LLVM_DEPENDENT_LIBRARIES section (https://llvm.org/docs/Extensions.html#sht-llvm-dependent-libraries-section-dependent-libraries). VTune should just ignore it, not crash.