This issue is to track C ABI compatibility support in the stage1 compiler.

Here's what support looks like currently:

• integers, floats, pointers, enums, bools work on every target, as parameters and return values
• x86_64: struct & union parameters & return values larger than 16 bytes
• x86_64: struct & union parameters that have at least 1 integer in them
• x86_64: struct & union parameters <= 16 bytes which break structs into parameters
• x86_64: struct & union parameters <= 16 bytes which are all floats
• x86_64: struct & union return values <= 16 bytes
• ARM: struct & union return values
• ARM: struct & union parameters
• C ABI for parameters that is unsupported gives a compile error linking to this issue
• C ABI for return values that is unsupported gives a compile error linking to this issue
• other architectures structs & unions parameters & return values

For those who find this issue from the compile error, leave a comment detailing your specific needs and I'll see if I can code those up for you to unblock you, so you don't have to wait for this issue to be 100% solved.