README.md: Document some widely-applicable troubleshooting tidbits

Author: solb

README.md

@@ -343,3 +343,52 @@ following GDB command to cover the preemption signal(s) affecting your task's ex
 ```
 (gdb) handle SIGALRM nopass
 ```
+
+
+Troubleshooting
+---------------
+**My distribution ships a version of glibc that is newer than 2.33.  What should I do?**
+
+Such versions are untested.  If you do not encounter any obvious issues, great!  Otherwise, no need
+to modify your installation; instead, just follow the steps under _Building glibc from source_ above
+to build version 2.33.  When linking your executable, you will want to use GCC's `-Wl,-I` switch
+(`-Clink-arg=-Wl,-I` in the case of rustc) to specify the newly-symlinked dynamic linker as the
+program's interpreter.  If you are building the program using Cargo and its source is located in
+tree or you have symlinked its `.cargo` to this repository's folder of the same name, passing the
+flag should happen automatically.  Note that, if you get any version errors when running the
+resulting binary, you may need to add a further `-L` and the path to the `lib` directory generated
+by the glibc `install` target to your linker flags and rebuild.
+
+**My distribution ships a version of elfutils that is newer than 0.176.  What should I do?**
+
+It probably does!  The easiest thing to do is to downgrade the package.  For instance, if using
+Debian, download (at least) the following binary packages from https://snapshot.debian.org:
+`libasm1`, `libasm-dev`, `libdw1`, `libelf1`, and `libelf-dev`.  Put the packages into a new
+directory, `cd` into it, and run `apt -s install ./*.deb`.  If it shows any dependency errors,
+download additional packages to address them and add them to the directory; you will probably need
+`gdb` version 9.2-1, `libpython3.8`, `libpython3.8-minimal`, and `libpython3.8-stdlib`.  Then
+perform the downgrade by running `sudo apt install ./*.deb`.
+
+**I get the assertion: `ELF64_ST_TYPE(st->st_info) != STT_GNU_IFUNC)`!**
+
+This appears to occur on some Ubuntu systems because of the way Canonical packages zlib (`libz.so`).
+The easiest workaround is to grab a closely matching package version from
+https://packages.debian.org and extract the shared library file.  Then either export the
+`$LD_LIBRARY_PATH` environment variable to the path to its containing folder when executing your
+application, or just place the shared library in the `lib` directory generated by glibc's `install`
+target if/when you built it from source.
+
+**I get some other error at some point.**
+
+Start by rerunning `./configure` to clean the build.  Make sure it finds all the dependencies.  Look
+back at _System requirements_ and verify that you are not on a `cargo` version affected by the
+regression, and that you have the described wrapper script in your `$PATH` if you have a
+sufficiently new version of `bindgen` (a shell alias will not suffice).
+
+Next, try building _libgotcha_ in isolation.  Just `cd` into `external/libgotcha` and type `make`
+(without passing `-j`).  If you get errors here, go back to the previous paragraph, pinch yourself,
+and check all that one more time.
+
+If you get this far, try building _libinger_ without per--preemptive function thread-local variables
+by passing `--features notls` to your Cargo command.  If you are still stuck, see whether you can
+trace the source of the error using any of the techniques under _Debugging tips_ above.