Add nightly-only support for Cargo unremap trim-paths files in rust-gdb

src/bootstrap/src/core/build_steps/dist.rs

@@ -748,6 +748,9 @@ impl Step for DebuggerScripts {
         cp_debugger_script("gdb_load_rust_pretty_printers.py");
         cp_debugger_script("gdb_lookup.py");
         cp_debugger_script("gdb_providers.py");
+        if builder.build.unstable_features() {
+            cp_debugger_script("gdb_trim_paths.py");
+        }
 
         // lldb debugger scripts
         builder.install(

src/etc/gdb_trim_paths.py

@@ -0,0 +1,105 @@
+# GDB Python script to handle Cargo `<exe>.trim-paths.jsonl` files from the trim-paths feature
+#  - https://github.com/rust-lang/cargo/issues/12137
+#  - https://github.com/rust-lang/rust/issues/111540
+
+import json
+import os
+import gdb
+import sys
+
+
+# https://doc.guix.gnu.org/gdb/16.3/en/html_node/Source-Path.html#index-set-substitute_002dpath
+def _process_v1_trim_paths(lines, trim_paths_path):
+    for idx, line in enumerate(lines[2:], start=3):
+        try:
+            entry = json.loads(line)
+            if "from" in entry and "to" in entry:
+                cmd = f'set substitute-path "{entry["from"]}" "{entry["to"]}"'
+                gdb.execute(cmd)
+        except json.JSONDecodeError:
+            print(
+                f"(rust-gdb) warning: invalid JSON on line {idx} of {trim_paths_path}",
+                file=sys.stderr,
+            )
+
+
+def _load_trim_paths(filepath):
+    trim_paths_path = f"{filepath}.trim-paths.jsonl"
+
+    # FIXME: It might be worth looking into the debuginfod fetch content if the local file
+    # doesn't exists (maybe with `debuginfod-find debuginfo`).
+    if not os.path.isfile(trim_paths_path):
+        return
+
+    try:
+        # Load all the lines of the trim-paths file
+        with open(trim_paths_path, "r", encoding="utf-8") as f:
+            lines = [line.strip() for line in f]
+
+        # Abort if we have less than 3 lines as that means that we cannot have any
+        # substitutions (header + metadata is already 2 lines)
+        if not lines or len(lines) < 3:
+            return
+
+        # Try loading the header line, which contains the version (v) field
+        try:
+            header = json.loads(lines[0])
+            ver = header["v"]
+        except json.JSONDecodeError:
+            print(
+                f"(rust-gdb) warning: header line 1 of {trim_paths_path} is not valid JSON",
+                file=sys.stderr,
+            )
+            return
+
+        # We only handle version 1
+        if ver == 1:
+            _process_v1_trim_paths(lines, trim_paths_path)
+        else:
+            print(
+                f"(rust-gdb) warning: unsupported trim-paths version {ver}: {trim_paths_path}",
+                file=sys.stderr,
+            )
+    except Exception as e:
+        print(
+            f"(rust-gdb) warning: failed to process trim-paths mappings: {e} of {trim_paths_path}",
+            file=sys.stderr,
+        )
+
+
+def _on_objfile(objfile):
+    filepath = objfile.filename
+
+    if not filepath or not objfile.is_valid() or not os.path.isfile(filepath):
+        return
+
+    _load_trim_paths(filepath)
+
+
+def _on_progspace(progspace):
+    filepath = progspace.filename
+
+    if not filepath or not os.path.isfile(filepath):
+        return
+
+    _load_trim_paths(filepath)
+
+
+def _on_new_objfile(event):
+    _on_objfile(event.new_objfile)
+
+
+def _on_executable_changed(event):
+    _on_progspace(event.progspace)
+
+
+# Setup the events for new objfile (so) and new executable
+# https://doc.guix.gnu.org/gdb/16.3/en/html_node/Events-In-Python.html
+#
+# FIXME: should we handle clear/free events?
+gdb.events.new_objfile.connect(_on_new_objfile)
+gdb.events.executable_changed.connect(_on_executable_changed)
+
+# Load the trim-paths files for the already loaded objfiles
+for objfile in gdb.objfiles():
+    _on_objfile(objfile)

src/etc/rust-gdb

@@ -16,13 +16,24 @@ GDB_PYTHON_MODULE_DIRECTORY="$RUSTC_SYSROOT/lib/rustlib/etc"
 # Get the commit hash for path remapping
 RUSTC_COMMIT_HASH="$("$RUSTC" -vV | sed -n 's/commit-hash: \([a-zA-Z0-9_]*\)/\1/p')"
 
-# Run GDB with the additional arguments that load the pretty printers
 # Set the environment variable `RUST_GDB` to overwrite the call to a
 # different/specific command (defaults to `gdb`).
 RUST_GDB="${RUST_GDB:-gdb}"
-PYTHONPATH="$PYTHONPATH:$GDB_PYTHON_MODULE_DIRECTORY" exec ${RUST_GDB} \
+
+# Run GDB with the additional arguments that load the pretty printers
+# Prepend base GDB flags ahead of any arguments passed by the user
+set -- \
   --directory="$GDB_PYTHON_MODULE_DIRECTORY" \
   -iex "add-auto-load-safe-path $GDB_PYTHON_MODULE_DIRECTORY" \
   -iex "set substitute-path /rustc/$RUSTC_COMMIT_HASH $RUSTC_SYSROOT/lib/rustlib/src/rust" \
   "$@"
-
+
+# Unstable (nightly-only) trim-paths feature, activated only if
+#  - RUST_GDB_TRIM_PATHS=unstable is set
+#  - and if the python file is present (only shipped on nightly)
+GDB_TRIM_PATHS="$GDB_PYTHON_MODULE_DIRECTORY/gdb_trim_paths.py"
+if [ "${RUST_GDB_TRIM_PATHS:-}" = "unstable" ] && [ -f "$GDB_TRIM_PATHS" ]; then
+  set -- -x "$GDB_TRIM_PATHS" "$@"
+fi
+
+PYTHONPATH="$PYTHONPATH:$GDB_PYTHON_MODULE_DIRECTORY" exec ${RUST_GDB} "$@"