C structure assignment uses memcpy

Question

I have this StructType st = StructTypeSecondInstance->st; and it generates a segfault. The strange part is when the stack backtrace shows me:

0x1067d2cc: memcpy + 0x10 (0, 10000, 1, 1097a69c, 11db0720, bfe821c0) + 310
0x103cfddc: some_function + 0x60 (0, bfe823d8, bfe82418, 10b09b10, 0, 0) +

So, does struct assigment use memcpy?

Answer 1

One can't tell. Small structs may even be kept in registers. Whether memcpy is used is an implementation detail (it's not even implementation-defined, or unspecified -- it's just something the compiler writer choses and does not need to document.)

From a C Standard point of view, all that matters is that after the assigment, the struct members of the destination struct compare equal to the corresponding members of the source struct.

I would expect compiler writers to make a tradeoff between speed and simplicity, probably based on the size of the struct, the larger the more likely to use a memcpy. Some memcpy implementations are very sophisticated and use different algorithms depending on whether the length is some power of 2 or not, or the alignment of the src and dst pointers. Why reinvent the wheel or blow up the code with an inline version of memcpy?