Kernel callstacks not show correct

[woodpenker]

hi, I am using version 885b4d5297c1633444317d439b312626920b5486 from libbpf-bootstrap with C API , when I set cfg like this:

src.src_type = SRC_T_KERNEL;
src.params.kernel.kallsyms = NULL;
src.params.kernel.kernel_image = NULL;

It shows like this:

fail to load the kernel image /usr/lib/debug/boot/vmlinux-4.18.0-22-generic
  0 [<ffffffff9dabc7a1>]
  1 [<ffffffff9e3f46ac>]
  2 [<ffffffff9e3f8989>]
  3 [<ffffffff9e3f8a73>]
  4 [<ffffffff9dcb6836>]
  5 [<ffffffff9dcb77d6>]
  6 [<ffffffff9dcb8473>]
  7 [<ffffffff9da042aa>]
  8 [<ffffffff9e400088>]

The /proc/kallsyms exists, but /usr/lib/debug/boot/vmlinux-4.18.0-22-generic don't. Also I know on some machine, there is no kernel_image, such as Xavier. When I try to not give src.params.kernel.kernel_image and run, it crashed.

Seems kernel sym trans failed and can it run with only provide kallsyms path?

[woodpenker]

BTW, it seems not correct to link C program with this -lrt -ldl -lpthread -lm libblazesym.a according to https://github.com/libbpf/blazesym#link-c-programs, such as gcc CMakeFiles/xx.dir/xx.c.o -o xx -lrt -ldl -lpthread -lm ./libblazesym.a libbpf/libbpf.a -lelf -lz, the ld program complains a lot like this:

/home/xx/.cargo/registry/src/github.com-1ecc6299db9ec823/nix-0.24.2/src/sys/timer.rs:162: undefined reference to `timer_getoverrun'
./libblazesym.a(nix-1d96e29aba325ff2.nix.dba0ec83-cgu.8.rcgu.o): In function `<nix::sys::timer::Timer as core::ops::drop::Drop>::drop':
/home/xx/.cargo/registry/src/github.com-1ecc6299db9ec823/nix-0.24.2/src/sys/timer.rs:169: undefined reference to `timer_delete'
collect2: error: ld returned 1 exit status

The sequence of the args matters. If I change it to libblazesym.a -lrt -ldl -lpthread -lm, such as gcc CMakeFiles/xx.dir/xx.c.o -o xx ./libblazesym.a -lrt -ldl -lpthread -lm libbpf/libbpf.a -lelf -lz, the ld succeed.

Maybe the doc needs to change the order?

My GCC version is 7.4.0.

[ThinkerYzu1]

I am looking into this issue.

[ThinkerYzu1]

@woodpenker pull #11 should fix your issue. It should work with only kallsyms or a kernel image. Please check if it fixes your problem. Thank you!

[woodpenker]

@woodpenker pull #11 should fix your issue. It should work with only kallsyms or a kernel image. Please check if it fixes your problem. Thank you!

👍 It works! I had tested it with the setting src.params.kernel.kallsyms = NULL and src.params.kernel.kallsyms = "/proc/kallsyms";, both work well. Thanks!