On Wednesday, 25 July 2018 at 08:37:28 UTC, Zheng (Vic) Luo wrote:
Current implementation of compilers assumes the existence of some symbols from libc, which leads to an infinite loop if we want to implement primitives like "memset" with our own code because the compiler will optimize consecutive set with "memset". This suggests that we cannot write a freestanding program without supports from compiler. With "-betterC" flag, dmd/gdc/ldc also come into this issue[5], which also applies to C/C++[1] and rust [2][3][4].
GDC doesn't seem to be affected. See https://explore.dgnu.org/g/ZJVjAu i.e. no recursive calls to `memset`, but I don't know if I just got lucky with my implementation.
It would be better to provide a standard flag like "-ffreestanding" (or -fno-builtin?) to disable such optimizations to facilitate freestanding programming instead of forcing the developers to hack around different compiler implementations, so I was wondering is there any progress on this problem?
According to https://wiki.dlang.org/Using_GDC, `-fno-builtin` is already there.
From my experience I haven't yet found a need for `-ffreestanding`, as GDC always seems to do the right thing for me. It does generate calls for `memset`, `memcmp`, etc..., but as long as I provide my own implementation with the correct symbol name as it expects (i.e. `memset` with no name mangling, a.k.a `extern(C) void* memset(void*, int, size_t)`) it seems to work fine.
Mike
