Use gcc feature __attribute__ section to create the custom sections on the runtime

[azubieta]

While looking for a solution for AppImageCommunity/libappimage#21 I found this nice gcc feature that will save us a lot of "fragile" cmake code at https://github.com/AppImage/AppImageKit/blob/master/src/build-runtime.cmake

Basically to create a 10 bites long section named foo we would use the code below
char custom_section[10] __attribute__((section("foo"))) = {0x0};

Documentation can be found here http://www.keil.com/support/man/docs/armcc/armcc_chr1359124982450.htm

Here is an example of how it's used to append metadata to the linux kernel modules:
https://www.bottomupcs.com/elf-sections-others.xhtml#modinfo_sections

[TheAssassin]

My plan for the future was to build a tool to take care of these things right before building the runtime, then build the runtime with it. We want to insert our magic bytes in a very custom location in the future, and that's the only way to do it properly.

That said, I'm open to using this extension. How well is that supported? Do other compilers (mainly clang) support that?

Can you run tests in AppImageBuild?

[azubieta]

There is a similar feature on clang http://www.keil.com/support/man/docs/armclang_ref/armclang_ref_cmf1493390581125.htm