Handle null from LLVMRustGetSectionName

Author: nitnelave

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -1736,7 +1736,9 @@ extern "C" {
     pub fn LLVMRustArchiveIteratorFree(AIR: &'a mut ArchiveIterator<'a>);
     pub fn LLVMRustDestroyArchive(AR: &'static mut Archive);
 
-    pub fn LLVMRustGetSectionName(SI: &SectionIterator<'_>, data: &mut *const c_char) -> size_t;
+    #[allow(improper_ctypes)]
+    pub fn LLVMRustGetSectionName(SI: &SectionIterator<'_>,
+                                  data: &mut Option<std::ptr::NonNull<c_char>>) -> size_t;
 
     #[allow(improper_ctypes)]
     pub fn LLVMRustWriteTwineToString(T: &Twine, s: &RustString);

src/librustc_codegen_llvm/metadata.rs

@@ -8,7 +8,6 @@ use rustc_data_structures::owning_ref::OwningRef;
 use rustc_codegen_ssa::METADATA_FILENAME;
 
 use std::path::Path;
-use std::ptr;
 use std::slice;
 use rustc_fs_util::path_to_c_string;
 
@@ -67,10 +66,14 @@ fn search_meta_section<'a>(of: &'a ObjectFile,
     unsafe {
         let si = mk_section_iter(of.llof);
         while llvm::LLVMIsSectionIteratorAtEnd(of.llof, si.llsi) == False {
-            let mut name_buf = ptr::null();
+            let mut name_buf = None;
             let name_len = llvm::LLVMRustGetSectionName(si.llsi, &mut name_buf);
-            let name = slice::from_raw_parts(name_buf as *const u8, name_len as usize).to_vec();
-            let name = String::from_utf8(name).unwrap();
+            let name = name_buf.map_or(
+                "".to_string(),
+                |buf| String::from_utf8(
+                    slice::from_raw_parts(buf.as_ptr() as *const u8,
+                                          name_len as usize)
+                    .to_vec()).unwrap());
             debug!("get_metadata_section: name {}", name);
             if read_metadata_section_name(target) == name {
                 let cbuf = llvm::LLVMGetSectionContents(si.llsi);