When you use inline assembly, in fact the compiler does preserve the semantics of the surrounding program considering the target's ABI -- if you tell it correct

When you use inline assembly, in fact the compiler does preserve the semantics of the surrounding program considering the target's ABI -- if you tell it correctly what impacts the inline asm has. Lots of rules must be followed in order to get this behavior just right. One of the most subtle ones is "early clobbers" [1]. In many cases, you can get all the benefits of inline assembly from compiler intrinsics while letting the compiler handle all the details of register allocation and scheduling. Note that in OP's case IIUC this was assembly code and not inline assembly. If you write functions in assembly you are solely responsible for calling conventions and ABI conformance. [1] https://stackoverflow.com/a/15819941/489590 https://stackoverflow.com/a/15819941/489590