moved dependency on pyelftools into scoped function where it's used to reduce the number of dependencies required overall

riscemu/priv/ElfLoader.py

@@ -1,9 +1,6 @@
 from dataclasses import dataclass
 from typing import List, Dict, Tuple
 
-from elftools.elf.elffile import ELFFile
-from elftools.elf.sections import Section, SymbolTableSection
-
 from .Exceptions import *
 from ..Exceptions import RiscemuBaseException
 from ..Executable import MemoryFlags, LoadedMemorySection
@@ -12,6 +9,9 @@ from ..helpers import FMT_PARSE, FMT_NONE, FMT_GREEN, FMT_BOLD
 
 FMT_ELF = FMT_GREEN + FMT_BOLD
 
+if typing.TYPE_CHECKING:
+    from elftools.elf.elffile import ELFFile
+    from elftools.elf.sections import Section, SymbolTableSection
 
 # This requires pyelftools package!
 
@@ -29,11 +29,18 @@ class ElfExecutable:
         self.sections_by_name = dict()
         self.symbols = dict()
 
+        try:
+            from elftools.elf.elffile import ELFFile
+            from elftools.elf.sections import Section, SymbolTableSection
+
             with open(name, 'rb') as f:
                 print(FMT_ELF + "[ElfLoader] Loading elf executable from: {}".format(name) + FMT_NONE)
                 self._read_elf(ELFFile(f))
+        except ImportError as e:
+            print(FMT_PARSE + "[ElfLoader] Cannot load elf files without PyElfTools package! You can install them using pip install pyelftools!" + FMT_NONE)
+            raise e
 
-    def _read_elf(self, elf: ELFFile):
+    def _read_elf(self, elf: 'ELFFile'):
         if not elf.header.e_machine == 'EM_RISCV':
             raise InvalidElfException("Not a RISC-V elf file!")
         if not elf.header.e_ident.EI_CLASS == 'ELFCLASS32':
@@ -41,6 +48,7 @@ class ElfExecutable:
 
         self.run_ptr = elf.header.e_entry
 
+        from elftools.elf.sections import SymbolTableSection
         for sec in elf.iter_sections():
             if isinstance(sec, SymbolTableSection):
                 self._parse_symtab(sec)
@@ -51,7 +59,7 @@ class ElfExecutable:
 
             self.add_sec(self._lms_from_elf_sec(sec, 'kernel'))
 
-    def _lms_from_elf_sec(self, sec: Section, owner: str):
+    def _lms_from_elf_sec(self, sec: 'Section', owner: str):
         is_code = sec.name in ('.text',)
         data = bytearray(sec.data())
         flags = MemoryFlags(is_code, is_code)
@@ -65,7 +73,7 @@ class ElfExecutable:
             owner
         )
 
-    def _parse_symtab(self, symtab: SymbolTableSection):
+    def _parse_symtab(self, symtab: 'SymbolTableSection'):
         self.symbols = {
             sym.name: sym.entry.st_value for sym in symtab.iter_symbols() if sym.name
         }