session: add split-dwarf flag

This commit adds a flag for Split DWARF, which enables debuginfo to be
split into multiple files.

Signed-off-by: David Wood <david@davidtw.co>

Author: davidtwco

compiler/rustc_session/src/config.rs

@@ -221,6 +221,23 @@ pub enum DebugInfo {
     Full,
 }
 
+/// Some debuginfo requires link-time relocation and some does not. LLVM can partition the debuginfo
+/// into sections depending on whether or not it requires link-time relocation. Split DWARF
+/// provides a mechanism which allows the linker to skip the sections which don't require link-time
+/// relocation - either by putting those sections into DWARF object files, or keeping them in the
+/// object file in such a way that the linker will skip them.
+#[derive(Clone, Copy, Debug, PartialEq, Hash)]
+pub enum SplitDwarfKind {
+    /// Disabled.
+    None,
+    /// Sections which do not require relocation are written into the object file but ignored
+    /// by the linker.
+    Single,
+    /// Sections which do not require relocation are written into a DWARF object (`.dwo`) file,
+    /// which is skipped by the linker by virtue of being a different file.
+    Split,
+}
+
 #[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
 #[derive(Encodable, Decodable)]
 pub enum OutputType {

compiler/rustc_session/src/options.rs

@@ -269,6 +269,7 @@ macro_rules! options {
         pub const parse_switch_with_opt_path: &str =
             "an optional path to the profiling data output directory";
         pub const parse_merge_functions: &str = "one of: `disabled`, `trampolines`, or `aliases`";
+        pub const parse_split_dwarf_kind: &str = "one of: `none`, `single` or `split`";
         pub const parse_symbol_mangling_version: &str = "either `legacy` or `v0` (RFC 2603)";
         pub const parse_src_file_hash: &str = "either `md5` or `sha1`";
         pub const parse_relocation_model: &str =
@@ -676,6 +677,19 @@ macro_rules! options {
             true
         }
 
+        fn parse_split_dwarf_kind(
+            slot: &mut SplitDwarfKind,
+            v: Option<&str>,
+        ) -> bool {
+            *slot = match v {
+                Some("none") => SplitDwarfKind::None,
+                Some("split") => SplitDwarfKind::Split,
+                Some("single") => SplitDwarfKind::Single,
+                _ => return false,
+            };
+            true
+        }
+
         fn parse_symbol_mangling_version(
             slot: &mut Option<SymbolManglingVersion>,
             v: Option<&str>,
@@ -1088,6 +1102,11 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "hash algorithm of source files in debug info (`md5`, `sha1`, or `sha256`)"),
     strip: Strip = (Strip::None, parse_strip, [UNTRACKED],
         "tell the linker which information to strip (`none` (default), `debuginfo` or `symbols`)"),
+    split_dwarf: SplitDwarfKind = (SplitDwarfKind::None, parse_split_dwarf_kind, [UNTRACKED],
+        "enable generation of split dwarf"),
+    split_dwarf_inlining: bool = (true, parse_bool, [UNTRACKED],
+        "provide minimal debug info in the object/executable to facilitate online \
+         symbolication/stack traces in the absence of .dwo/.dwp files when using Split DWARF"),
     symbol_mangling_version: Option<SymbolManglingVersion> = (None,
         parse_symbol_mangling_version, [TRACKED],
         "which mangling version to use for symbol names ('legacy' (default) or 'v0')"),