1 files changed, 112 insertions, 0 deletions
diff --git a/compiler/rustc_codegen_llvm/src/metadata.rs b/compiler/rustc_codegen_llvm/src/metadata.rs
new file mode 100644
index 00000000000..9036428c04b
--- /dev/null
+++ b/compiler/rustc_codegen_llvm/src/metadata.rs
@@ -0,0 +1,112 @@
+use crate::llvm;
+use crate::llvm::archive_ro::ArchiveRO;
+use crate::llvm::{mk_section_iter, False, ObjectFile};
+use rustc_middle::middle::cstore::MetadataLoader;
+use rustc_target::spec::Target;
+
+use rustc_codegen_ssa::METADATA_FILENAME;
+use rustc_data_structures::owning_ref::OwningRef;
+use rustc_data_structures::rustc_erase_owner;
+use tracing::debug;
+
+use rustc_fs_util::path_to_c_string;
+use std::path::Path;
+use std::slice;
+
+pub use rustc_data_structures::sync::MetadataRef;
+
+pub struct LlvmMetadataLoader;
+
+impl MetadataLoader for LlvmMetadataLoader {
+    fn get_rlib_metadata(&self, _: &Target, filename: &Path) -> Result<MetadataRef, String> {
+        // Use ArchiveRO for speed here, it's backed by LLVM and uses mmap
+        // internally to read the file. We also avoid even using a memcpy by
+        // just keeping the archive along while the metadata is in use.
+        let archive =
+            ArchiveRO::open(filename).map(|ar| OwningRef::new(Box::new(ar))).map_err(|e| {
+                debug!("llvm didn't like `{}`: {}", filename.display(), e);
+                format!("failed to read rlib metadata in '{}': {}", filename.display(), e)
+            })?;
+        let buf: OwningRef<_, [u8]> = archive.try_map(|ar| {
+            ar.iter()
+                .filter_map(|s| s.ok())
+                .find(|sect| sect.name() == Some(METADATA_FILENAME))
+                .map(|s| s.data())
+                .ok_or_else(|| {
+                    debug!("didn't find '{}' in the archive", METADATA_FILENAME);
+                    format!("failed to read rlib metadata: '{}'", filename.display())
+                })
+        })?;
+        Ok(rustc_erase_owner!(buf))
+    }
+
+    fn get_dylib_metadata(&self, target: &Target, filename: &Path) -> Result<MetadataRef, String> {
+        unsafe {
+            let buf = path_to_c_string(filename);
+            let mb = llvm::LLVMRustCreateMemoryBufferWithContentsOfFile(buf.as_ptr())
+                .ok_or_else(|| format!("error reading library: '{}'", filename.display()))?;
+            let of =
+                ObjectFile::new(mb).map(|of| OwningRef::new(Box::new(of))).ok_or_else(|| {
+                    format!("provided path not an object file: '{}'", filename.display())
+                })?;
+            let buf = of.try_map(|of| search_meta_section(of, target, filename))?;
+            Ok(rustc_erase_owner!(buf))
+        }
+    }
+}
+
+fn search_meta_section<'a>(
+    of: &'a ObjectFile,
+    target: &Target,
+    filename: &Path,
+) -> Result<&'a [u8], String> {
+    unsafe {
+        let si = mk_section_iter(of.llof);
+        while llvm::LLVMIsSectionIteratorAtEnd(of.llof, si.llsi) == False {
+            let mut name_buf = None;
+            let name_len = llvm::LLVMRustGetSectionName(si.llsi, &mut name_buf);
+            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);
+                let csz = llvm::LLVMGetSectionSize(si.llsi) as usize;
+                // The buffer is valid while the object file is around
+                let buf: &'a [u8] = slice::from_raw_parts(cbuf as *const u8, csz);
+                return Ok(buf);
+            }
+            llvm::LLVMMoveToNextSection(si.llsi);
+        }
+    }
+    Err(format!("metadata not found: '{}'", filename.display()))
+}
+
+pub fn metadata_section_name(target: &Target) -> &'static str {
+    // Historical note:
+    //
+    // When using link.exe it was seen that the section name `.note.rustc`
+    // was getting shortened to `.note.ru`, and according to the PE and COFF
+    // specification:
+    //
+    // > Executable images do not use a string table and do not support
+    // > section names longer than 8 characters
+    //
+    // https://docs.microsoft.com/en-us/windows/win32/debug/pe-format
+    //
+    // As a result, we choose a slightly shorter name! As to why
+    // `.note.rustc` works on MinGW, that's another good question...
+
+    if target.options.is_like_osx { "__DATA,.rustc" } else { ".rustc" }
+}
+
+fn read_metadata_section_name(_target: &Target) -> &'static str {
+    ".rustc"
+}