If you remember C memcpy‘s arg order, and how rep movsb works, that’s most of the way to remembering x86-64 System V. The design makes memcpy(dst, src, size) cheap to implement with rep movsb, except leaving RCX unused in more functions because it’s needed for variable-count shifts more often than anything needs RDX. Then R8 … Read more
Basically, just make sure the public interface to your library does not expose Boost. You can always use it however much you want internally. Generally, having the interface of a library depend on another library is bad (unless it depends on a standard library like STL). Boost almost fits into the “standard” library category, but … Read more
The freedom to implement things in the most natural way on each processor. I imagine that c in particular has conforming implementations on more different architectures than any other language. Abiding by a ABI optimized for the currently common, high-end, general-purpose CPUs would require unnatural contortions on some the odder machines out there.
In C++ the bit representation (and even the size) of a bool is implementation defined; generally it’s implemented as a char-sized type taking 1 or 0 as possible values. If you set its value to anything different from the allowed ones (in this specific case by aliasing a bool through a char and modifying its … Read more
The trick is that you tell them somehow else. For printf you have to supply a format string which even contains type information (which might be incorrect though). The way to supply this information is mainly user-contract and often error-prone. As for calling conventions: Usually the arguments are pushed onto the stack from left to … Read more
This depends entirely on the ABI for each platform. Since you mention eax and ebx let’s see what’s the case for x86 (as of Linux v5.17.5). In fs/binfmt_elf.c, inside load_elf_binary(), the kernel checks if the ABI specifies any requirements for register values at program loading: /* * The ABI may specify that certain registers be … Read more
Alignment helps the CPU fetch data from memory in an efficient manner: less cache miss/flush, less bus transactions etc. Some memory types (e.g. RDRAM, DRAM etc.) need to be accessed in a structured manner (aligned “words” and in “burst transactions” i.e. many words at one time) in order to yield efficient results. This is due … Read more
Many modern Android devices (i.e. Nexus 5x) have AArch64 processors with arm64-v8a instruction set. Both – armeabi and armeabi-v7a – libraries run fine on these modern devices. Therefore, we can assume the answer to your question to be ‘YES’. See this for a breakdown of ABI management on Android: https://developer.android.com/ndk/guides/abis.html
None; no copies are done. The address of the caller’s Data return value is actually passed as a hidden argument to the function, and the createData function simply writes into the caller’s stack frame. This is known as the named return value optimisation. Also see the c++ faq on this topic. commercial-grade C++ compilers implement … Read more
The ABI specification is defined here. A newer version is available here. I assume the reader is accustomed to the terminology of the document and that they can classify the primitive types. If the object size is larger than two eight-bytes, it is passed in memory: struct foo { unsigned long long a; unsigned long … Read more