The pager_fallback() runs in the forked child process.
As such, it can only use functions from `man signal-safety`
or that are explicitly allowed.
We are mostly good, but g_printerr() is not allowed. It can deadlock.
Just avoid it. It's not very to print those error messages anyway.
setenv() cannot be called after fork, because it might allocate memory,
which can deadlock.
Instead, prepare the environment and use execvpe().
`man 2 fork` says:
After a fork() in a multithreaded program, the child can safely call
only async-signal-safe functions (see signal-safety(7)) until such time
as it calls execve(2).
This means, we are quite strongly limited what can be done in the child
process, before exec. setenv() is not listed as async-signal-safe, obviously
because it allocates memory, and malloc() isn't async-signal-safe either.
See also glib's documentation of GSpawnChildSetupFunc ([1]) about what
can be done in the child process.
[1] 08cb200aec/glib/gspawn.h (L124)
These variants provide additional nm_assert() checks, and are thus
preferable.
Note that we cannot just blindly replace &g_array_index() with
&nm_g_array_index(), because the latter would not allow getting a
pointer at index [arr->len]. That might be a valid (though uncommon)
usecase. The correct replacement of &g_array_index() is thus
nm_g_array_index_p().
I checked the code manually and replaced uses of nm_g_array_index_p()
with &nm_g_array_index(), if that was a safe thing to do. The latter
seems preferable, because it is familar to &g_array_index().
We use clang-format for automatic formatting of our source files.
Since clang-format is actively maintained software, the actual
formatting depends on the used version of clang-format. That is
unfortunate and painful, but really unavoidable unless clang-format
would be strictly bug-compatible.
So the version that we must use is from the current Fedora release, which
is also tested by our gitlab-ci. Previously, we were using Fedora 34 with
clang-tools-extra-12.0.1-1.fc34.x86_64.
As Fedora 35 comes along, we need to update our formatting as Fedora 35
comes with version "13.0.0~rc1-1.fc35".
An alternative would be to freeze on version 12, but that has different
problems (like, it's cumbersome to rebuild clang 12 on Fedora 35 and it
would be cumbersome for our developers which are on Fedora 35 to use a
clang that they cannot easily install).
The (differently painful) solution is to reformat from time to time, as we
switch to a new Fedora (and thus clang) version.
Usually we would expect that such a reformatting brings minor changes.
But this time, the changes are huge. That is mentioned in the release
notes [1] as
Makes PointerAligment: Right working with AlignConsecutiveDeclarations. (Fixes https://llvm.org/PR27353)
[1] https://releases.llvm.org/13.0.0/tools/clang/docs/ReleaseNotes.html#clang-format
