Function jemalloc_ctl::raw::read_str_mib

pub unsafe fn read_str_mib(mib: &[usize]) -> Result<&'static [u8]>

Uses the MIB mib as key to the MALLCTL NAMESPACE and reads its value.

The name_to_mib API translates a string of the key (e.g. arenas.nbins) to a mib (Management Information Base).

Safety

This function is unsafe because if the key does not return a pointer to a null-terminated string the behavior is undefined.

For example, a key for a u64 value can be used to read a pointer on 64-bit platform, where this pointer will point to the address denoted by the u64s representation. Also, a key to a *mut extent_hooks_t will return a pointer that will not point to a null-terminated string.

This function needs to compute the length of the string by looking for the null-terminator: \0. This requires reading the memory behind the pointer.

If the pointer is invalid (e.g. because it was converted from a u64 that does not represent a valid address), reading the string to look for \0 will dereference a non-dereferenceable pointer, which is undefined behavior.

If the pointer is valid but it does not point to a null-terminated string, looking for \0 will read garbage and might end up reading out-of-bounds, which is undefined behavior.