On C extensions, portability, and alternative compilers

Writing portable C code is impractical because real-world code relies on non-standard extensions and library quirks; glibc’s sys/cdefs.h uses GCC-predefined macros to conditionally map __attribute__((packed)) for structs like epoll_event, where ignoring it breaks ABI on 64-bit. POSIX also requires limits.h to define system-specific constants, forcing compilers to include platform files alongside builtins, and SDL_endian.h attempts to use GCC-style inline assembly even for unknown compilers that define ISA macros. These examples highlight how deeply embedded compiler assumptions create barriers for alternative C compilers, a reality the author experienced while building their own.

• Test your toolchain against non-GCC compilers early, especially when relying on glibc or POSIX headers that contain hidden compiler-specific dependencies.