Mmap () returns EINVAL

Question

I cannot get the mmap function to work. It returns an EINVAL error code.

void* mapped = 
        mmap((void*)(map_addr + slide),
             map_size,
             PROT_WRITE | PROT_READ,
             MAP_PRIVATE | MAP_ANON,
             bprm->file,
             map_offset);

I checked the documentation for this feature on my platform ( Darwin ), and there seems to be something wrong. The man page for mmap presents four cases in which EINVAL will be returned.

 [EINVAL]           MAP_FIXED was specified and the addr argument was not page
                    aligned, or part of the desired address space resides out of the
                    valid address space for a user process.

MAP_FIXED is not specified, so it is not.

 [EINVAL]           flags does not include either MAP_PRIVATE or MAP_SHARED.

MAP_PRIVATE is present.

 [EINVAL]           The len argument was negative.

The argument len ​​(map_size) during the call is 8192.

 [EINVAL]           The offset argument was not page-aligned based on the page size as
                    returned by getpagesize(3).

The offset (map_offset) argument is 0, so it should be page aligned. (maybe I'm wrong?)

Answer 1

Are you sure to read the first description? It could also be read as a description of two disjoint cases:

• MAP_FIXED , addr ,
• .

, map_addr + slide .

Answer 2

NULL addr mmaped ( ), .