[documentation] clarification about the signal safe stack tracing

[bertulli]

Hi, first of all thanks for your work. I was trying to integrate cpptrace in my project to investigate signal faults (specifically SIGSEGV), and I noticed a few things:

• the document on signal safe stack tracing mentions two files (signal_demo.cpp and signal_tracer.cpp), that are broken links
• in the example code, there is this for loop:

  for(std::size_t i = 0; i < count; i++) {
      cpptrace::safe_object_frame frame;
      cpptrace::get_safe_object_frame(buffer[i], &frame);
      write(input_pipe.write_end, &frame, sizeof(frame));
  }

  but the variable count is not defined. Since it is the limit of buffer, a frame_ptr, how should I extract the size of it?

As a side note, it's mentioned in #126 that older versions of glibc can't print the traces: do you know what is the minimum version?

Thanks!

[jeremy-rifkin]

Hi, thanks for pointing out the broken links. I’ll fix them tonight (or accept a PR), the files are in https://github.com/jeremy-rifkin/cpptrace/tree/main/test. The count in question comes from the generate safe raw trace function,

std::size_t count = cpptrace::safe_generate_raw_trace(…);

The minimum glibc version is 2.35, released in early 2022. Unfortunately it’s a relatively high glibc requirement but _dl_find_object is the only way to do this in a truly signal-safe way, as far as I have found.

[jeremy-rifkin]

I've pushed some fixes to the documentation in e8fce3fad1d299bb4effbe5af701bbc9bbd10ab5