Auto merge of #62460 - RalfJung:llvm-null, r=eddyb

 Handle null from LLVMRustGetSectionName

As part of https://github.com/rust-lang/rust/pull/58783 and https://github.com/rust-lang/rust/pull/62103, this incorrect use of a NULL pointer was found in the interface to LLVM. That PR is stuck with some linker issues, but there is no reason the soundness fix should have to wait for that.

diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index a5c295cd4525c25304aecf06828faa3f18108222..708ba79ec3ab238b4051f2071c4c4311f560282a 100644 (file)
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -1736,7 +1736,9 @@ pub fn LLVMRustArchiveIteratorNext(
     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);

diff --git a/src/librustc_codegen_llvm/metadata.rs b/src/librustc_codegen_llvm/metadata.rs
index 7cf497cb5d036afb75215668121a1b314a12e511..cd7255888118cd9747f6693a94eeb270241694d6 100644 (file)
--- a/src/librustc_codegen_llvm/metadata.rs
+++ b/src/librustc_codegen_llvm/metadata.rs
@@ -8,7 +8,6 @@
 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 +66,16 @@ 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(
+                String::new(), // We got a NULL ptr, ignore `name_len`.
+                |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);