Support interposing a (very basic) gdb script that sets debug file pa…

…ths in the `sources` command. (#3714)

CMakeLists.txt

@@ -793,6 +793,9 @@ install(FILES "${CMAKE_CURRENT_BINARY_DIR}/src/preload/rr_page.ld"
 configure_file("${CMAKE_CURRENT_SOURCE_DIR}/scripts/rr-collect-symbols.py"
                "${CMAKE_CURRENT_BINARY_DIR}/bin/rr-collect-symbols.py"
                COPYONLY)
+configure_file("${CMAKE_CURRENT_SOURCE_DIR}/scripts/rr-gdb-script-host.py"
+               "${CMAKE_CURRENT_BINARY_DIR}/bin/rr-gdb-script-host.py"
+               COPYONLY)
 
 install(PROGRAMS scripts/signal-rr-recording.sh
                  scripts/rr-collect-symbols.py

scripts/rr-gdb-script-host.py

@@ -0,0 +1,184 @@
+#!/usr/bin/env python3
+""" rr-gdb-script-host.py <user-gdb-script> <primary binary name>"""
+# Performs a limited emulation of the runtime environment of gdb scripts so that
+# we can run them for `rr sources` to locate debug information.
+from typing import Optional, List, Callable
+import logging
+import os
+import signal
+import sys
+
+def strip_prefix(s: str, needle: str) -> Optional[str]:
+    if s.startswith(needle):
+        return s[len(needle):]
+
+    return None
+
+GdbNewObjfileEventCallback = Callable[[object], None]
+
+class GdbScriptHost:
+    """ The filename of the main symbol file """
+    _filename: str = ""
+    """ The current value of the gdb dir """
+    _dir: str = ""
+    """ The current value of debug-file-directory """
+    debug_file_directory: str = "/usr/lib/debug"
+
+    new_objfile_events: List[GdbNewObjfileEventCallback] = []
+
+    def __init__(self, *args, **kwargs):
+        self._filename = args[0]
+
+    def show(self, cmd: str) -> Optional[str]:
+        cmd.rstrip()
+        if cmd == "debug-file-directory":
+            return self.debug_file_directory
+        if cmd == "dir":
+            return "Source directories searched: %s:$cdir:$cwd"%self._dir
+
+        return None
+
+    def set(self, cmd: str) -> str:
+        dfd = strip_prefix(cmd, "debug-file-directory ")
+        if dfd:
+            self.debug_file_directory = dfd
+            # Prints nothing upon success.
+            return ""
+
+        # This seems to be the default error message.
+        return "No symbol table is loaded.  Use the \"file\" command."
+
+    def execute_script(self, script: str):
+        gdb_api: GdbApiRoot = GdbApiRoot(self)
+        exec(script, {'gdb': gdb_api})
+
+    def new_objfile(self, f: str):
+        new_objfile: GdbNewObjfile = GdbNewObjfile(self, f)
+        new_objfile_event: GdbNewObjfileEvent = GdbNewObjfileEvent(self, new_objfile)
+        for callback in self.new_objfile_events:
+            callback(new_objfile_event)
+
+class GdbApiObject(object):
+    def __init__(self, *args, **kwargs):
+        self.gdb = args[0]
+
+    def __getattr__(self, attr):
+        logging.warning("Accessing unsupported GDB api %s.%s" % (self.__class__.__name__, attr))
+
+class GdbProgspace(GdbApiObject):
+    filename: str
+
+    def __init__(self, *args, **kwargs):
+        GdbApiObject.__init__(self, *args, **kwargs)
+        self.filename = self.gdb._filename
+
+class GdbNewObjfile(GdbApiObject):
+    filename: str
+    def __init__(self, *args, **kwargs):
+        GdbApiObject.__init__(self, *args, **kwargs)
+        self.filename = args[1]
+
+class GdbNewObjfileEvent(GdbApiObject):
+    new_objfile: GdbNewObjfile
+
+    def __init__(self, *args, **kwargs):
+        GdbApiObject.__init__(self, *args, **kwargs)
+        self.new_objfile = args[1]
+
+class GdbNewObjfileEvents(GdbApiObject):
+    def connect(self, c: GdbNewObjfileEventCallback):
+        logging.debug("EventRegistry.connect")
+        self.gdb.new_objfile_events.append(c)
+
+class GdbApiEvents(GdbApiObject):
+    _new_objfile: Optional[GdbNewObjfileEvents] = None
+
+    @property
+    def new_objfile(self) -> GdbNewObjfileEvents:
+        logging.debug("gdb.events.new_objfile")
+        if self._new_objfile == None:
+            self._new_objfile = GdbNewObjfileEvents(self.gdb)
+        return self._new_objfile
+
+class GdbApiRoot(GdbApiObject):
+    _events: Optional[GdbApiEvents] = None
+    _current_progspace: Optional[GdbProgspace] = None
+
+    def execute(self, command: str, from_tty: bool = False, to_string: bool = False) -> Optional[str]:
+        logging.debug("gdb.execute(\"%s\", from_tty=%s, to_string=%s)"%(command, str(from_tty), str(to_string)))
+        if from_tty:
+            logging.warning("Unsupported gdb.execute with from_tty == True")
+            return None
+
+        remainder = strip_prefix(command, "show ")
+        if remainder:
+            r = self.gdb.show(remainder)
+            if to_string:
+                return r
+            else:
+                print(r, file=sys.stderr)
+                return None
+        remainder = strip_prefix(command, "set ")
+        if remainder:
+            r = self.gdb.set(remainder)
+            if to_string:
+                return r
+            else:
+                print(r, file=sys.stderr)
+                return None
+        remainder = strip_prefix(command, "dir ")
+        if remainder:
+            self.gdb._dir = remainder
+            s = "Source directories searched: %s:$cdir:$cwd"%remainder
+            if to_string:
+                return s
+            else:
+                print(s, file=sys.stderr)
+                return None
+
+        logging.warning("Unsupported gdb.execute \"%s\""%command)
+        return None
+
+    def lookup_global_symbol(self, s: str) -> Optional[object]:
+        #logging.debug("gdb.lookup_global_symbol(\"%s\")"%s)
+        logging.warning("gdb.lookup_global_symbol(\"%s\") is not yet implemented, pretending we found something"%s)
+        return object()
+
+    def current_progspace(self) -> GdbProgspace:
+        logging.debug("gdb.current_progspace()")
+        if self._current_progspace == None:
+            self._current_progspace = GdbProgspace(self.gdb)
+        return self._current_progspace
+
+    @property
+    def events(self) -> GdbApiEvents:
+        logging.debug("gdb.events")
+        if self._events == None:
+            self._events = GdbApiEvents(self.gdb)
+        return self._events
+
+if __name__ == '__main__':
+    with open(sys.argv[1], 'r') as user_script_file:
+        user_script = user_script_file.read()
+        host = GdbScriptHost(sys.argv[2])
+        try:
+            host.execute_script(user_script)
+        except NameError as e:
+            if getattr(e, "name", None) == "python" or e == "NameError: name 'python' is not defined":
+                # This might be a gdb script that wraps a python script.
+                start = user_script.find("python") + len("python")
+                end = user_script.find("end")
+                if end == -1:
+                    raise(e)
+                user_script = user_script[start:end]
+                try:
+                    host.execute_script(user_script)
+                except:
+                    raise(e)
+
+        print("%s\n%s" % (host.debug_file_directory, host._dir), flush=True)
+        for line in sys.stdin:
+            line = line.rstrip()
+            logging.debug("Processing %s"%line)
+            host.new_objfile(line)
+            print("%s\n%s" % (host.debug_file_directory, host._dir), flush=True)

src/ElfReader.cc

@@ -541,7 +541,7 @@ DwarfSpan ElfReader::dwarf_section(const char* name, bool known_to_be_compressed
   offsets.compressed |= known_to_be_compressed;
   if (offsets.start && offsets.compressed) {
     auto decompressed = impl().decompress_section(offsets);
-    return DwarfSpan(&decompressed->front(), &decompressed->back());
+    return DwarfSpan(decompressed->data(), decompressed->data() + decompressed->size());
   }
   return DwarfSpan(map + offsets.start, map + offsets.end);
 }