"Generating […].gir with a custom command" / "g-ir-scanner" fails when building with crossdirect for armv7

This issue summarizes what we've seen in build.postmarketos.org#152 (closed) and pmaports#2820 (closed).

• Building some GTK projects for armv7 fails when running g-ir-scanner with various asserts.
• Apparently the bug does not always happen (build.postmarketos.org#152 (comment 469485)).
• It is reliably worked around when disabling crossdirect (v1 and upcoming v2 !2474 (comment 469455)) by using options="!pmb:crossdirect" in the APKBUILD.

What does crossdirect do?

• When crossdirect is disabled, armv7 binaries are used for all parts of the build, running through QEMU.
• When crossdirect is enabled, the x86_64 binary of the gcc-armv7 cross compiler gets used instead of running gcc through QEMU. armv7 g-ir-scanner still runs through QEMU.

Where is the bug?

My current theory is the following.

The bug is in one of these components, or possibly in multiple:

• gcc (when built as cross compiler for x86_64 -> armv7)
• QEMU
• build-system (meson)
• g-ir-scanner

It looks like binaries generated by gcc armv7 through QEMU vs. gcc to armv7 cross compiler are slightly different (which could be a bug in QEMU or gcc).

g-ir-scanner then runs into asserts for those, which could be:

• a bug in g-ir-scanner
• a bug in QEMU
• a bug in mesonbuild
• not a bug if the binaries generated earlier are really broken in a way they trigger the asserts

Next steps

To analyze this further, we could diff the binaries generated with/without crossdirect.

• Are they really different? If not, then my theory above does not make sense.
• Where are they different?
• What caused them to be different? (gcc or qemu?)
• Are they valid or not? (-> do the asserts trigger properly?)

(I won't spend more time on this now, but for future reference.)

Error messages

Phosh (from build.postmarketos.org#152 (closed)):

(process:12516): GLib-GObject-CRITICAL **: 19:01:31.389: g_param_spec_double: assertion 'default_value >= minimum && default_value <= maximum' failed
(process:12516): GLib-GObject-CRITICAL **: 19:01:31.390: validate_pspec_to_install: assertion 'G_IS_PARAM_SPEC (pspec)' failed
(process:12516): GLib-GObject-CRITICAL **: 19:01:31.390: g_param_spec_ref_sink: assertion 'G_IS_PARAM_SPEC (pspec)' failed
(process:12516): GLib-GObject-CRITICAL **: 19:01:31.391: g_param_spec_unref: assertion 'G_IS_PARAM_SPEC (pspec)' failed
qemu: uncaught target signal 11 (Segmentation fault) - core dumped

Mutter (pmaports#2820 (closed)):

(process:56814): GLib-GObject-CRITICAL **: 18:33:05.900: validate_pspec_to_install: assertion 'G_IS_PARAM_SPEC (pspec)' failed
(process:56814): GLib-GObject-CRITICAL **: 18:33:05.901: g_param_spec_ref_sink: assertion 'G_IS_PARAM_SPEC (pspec)' failed
(process:56814): GLib-GObject-CRITICAL **: 18:33:05.901: g_param_spec_unref: assertion 'G_IS_PARAM_SPEC (pspec)' failed
qemu: uncaught target signal 11 (Segmentation fault) - core dumped