Summary:
The implementation of `llvm_struct_name` before this diff calls
`caml_copy_string`, which allocates, while the `result` local variable
points to a block allocated by `caml_alloc_small` that has not yet
been initialized. If the allocation in `caml_copy_string` triggers a
garbage collection, then the GC root `result` contains a pointer to
uninitialized data, which may crash the GC or lead to a memory
corruption.
This diff fixes this by allocating and initializing the string first
and then allocating and initializing the option, thereby leaving no
dangling pointers when allocations are made.
The conversion from a C string to an OCaml string option is refactored
into a function, `cstr_to_string_option`. This function is also used
to simplify the definitions of `llvm_get_mdstring` and
`llvm_string_of_const`.
Upstream Differential Revision: https://reviews.llvm.org/D99393
Reviewed By: ngorogiannis
Differential Revision: D27360848
fbshipit-source-id: f2daa7561
Josh Berdine
cd9b64bd41