This implementation never changes actual memory protection, but it does
verify that the address range and flags are valid. The direct motivation
is fixing a linker error where LLVM links to `mprotect` in dead code.
Before this commit, he header of a mapped area, `struct map`, was
defined as follows:
struct map {
int prot;
int flags;
off_t offset;
size_t length;
char body[];
};
Because the size and alignment of an `off_t` is 8 bytes, the entire
structure was padded to 24 bytes. However, the offset of `body` into
`struct map` was only 20 bytes. Therefore the code in mmap() and
munmap() did not agree on the offset from header to body.
This commit changes mmap() to skip the entire header, which is what
munmap() expects and what the size calculation uses.
For now, this means using `//`-style comments in .c source files (though
not public header files), and spaces rather than tabs. No strong opinion
here; this is just what the majority of the current code is using.
This also synchronizes basics/crt/crt1.c with libc-bottom-half's
version, though this is just a cleanup as the former isn't currently used
by the main wasi-libc build.
