Interpreting segfault messages

This is a segfault due to following a null pointer trying to find code to run (that is, during an instruction fetch).

If this were a program, not a shared library

Run addr2line -e yourSegfaultingProgram 00007f9bebcca90d (and repeat for the other instruction pointer values given) to see where the error is happening. Better, get a debug-instrumented build, and reproduce the problem under a debugger such as gdb.

Since it’s a shared library

You’re hosed, unfortunately; it’s not possible to know where the libraries were placed in memory by the dynamic linker after-the-fact. Reproduce the problem under gdb.

What the error means

Here’s the breakdown of the fields:

• address (after the at) – the location in memory the code is trying to access (it’s likely that 10 and 11 are offsets from a pointer we expect to be set to a valid value but which is instead pointing to 0)

• ip – instruction pointer, ie. where the code which is trying to do this lives

• sp – stack pointer

• error – An error code for page faults; see below for what this means on x86 (link).

  /*
   * Page fault error code bits:
   *
   *   bit 0 ==    0: no page found       1: protection fault
   *   bit 1 ==    0: read access         1: write access
   *   bit 2 ==    0: kernel-mode access  1: user-mode access
   *   bit 3 ==                           1: use of reserved bit detected
   *   bit 4 ==                           1: fault was an instruction fetch
   *   bit 5 ==                           1: protection keys block access
   *   bit 15 ==                          1: SGX MMU page-fault
   */