Re: [PATCH 11/24] elf: Add a way to read segment information from an ELF file

On 08/02/2022 21:49, Simon Glass wrote:

Add a function which reads the segments and the entry address.

Also fix a comment nit in the tests while we are here.

Signed-off-by: Simon Glass sjg@chromium.org

tools/binman/elf.py | 37 +++++++++++++++++++++++++++++++++++++ tools/binman/elf_test.py | 31 +++++++++++++++++++++++++++++-- 2 files changed, 66 insertions(+), 2 deletions(-)

diff --git a/tools/binman/elf.py b/tools/binman/elf.py index de2bb4651f..2b83ac1876 100644 --- a/tools/binman/elf.py +++ b/tools/binman/elf.py @@ -20,6 +20,7 @@ from patman import tout ELF_TOOLS = True try: from elftools.elf.elffile import ELFFile

• from elftools.elf.elffile import ELFError from elftools.elf.sections import SymbolTableSection

except: # pragma: no cover ELF_TOOLS = False @@ -369,3 +370,39 @@ def UpdateFile(infile, outfile, start_sym, end_sym, insert): newdata += data[syms[end_sym].offset:] tools.WriteFile(outfile, newdata) tout.Info('Written to offset %#x' % syms[start_sym].offset)

+def read_segments(data):

• """Read segments from an ELF file
• Args:

•    data (bytes): Contents of file
  

• Returns:

•    tuple:
  

•        list of segments, each:
  

•            int: Segment number (0 = first)
  

•            int: Start address of segment in memory
  

•            bytes: Contents of segment
  

•        int: entry address for image
  

• Raises:

•    ValueError: elftools is not available
  

... or input data is not a correct ELF file?

• """
• if not ELF_TOOLS:

•    raise ValueError('Python elftools package is not available')
  

I see something like ModuleNotFoundError("No module named 'elftools'") when I try to import an unavailable module, so maybe this could match that.

• with io.BytesIO(data) as inf:

•    try:
  

•        elf = ELFFile(inf)
  

•    except ELFError as err:
  

•        raise ValueError(err)
  

Could also be: raise ValueError("Not an ELF file") from err

But I guess you want err's message here to match on it in tests. (It's also possible but slightly inconvenient with __cause__ when using raise-from)

•    entry = elf.header['e_entry']
  

•    segments = []
  

•    for i in range(elf.num_segments()):
  

•        segment = elf.get_segment(i)
  

•        if segment['p_type'] != 'PT_LOAD' or not segment['p_memsz']:
  

I can't say I fully understand ELF details, is it obvious in context that a function named read_segments() would only return these segments, or should the name be explicit about it e.g. read_loadable_segments()?

•            skipped = 1  # To make code-coverage see this line
  

•            continue
  

•        start = segment['p_offset']
  

•        rend = start + segment['p_filesz']
  

•        segments.append((i, segment['p_paddr'], data[start:rend]))
  

• return segments, entry

diff --git a/tools/binman/elf_test.py b/tools/binman/elf_test.py index f727258487..369260c17a 100644 --- a/tools/binman/elf_test.py +++ b/tools/binman/elf_test.py @@ -56,8 +56,8 @@ class FakeSection: def BuildElfTestFiles(target_dir): """Build ELF files used for testing in binman

• This compiles and links the test files into the specified directory. It the
• Makefile and source files in the binman test/ directory.

• This compiles and links the test files into the specified directory. It uses

• the Makefile and source files in the binman test/ directory.

  Args: target_dir: Directory to put the files into

@@ -258,6 +258,33 @@ class TestElf(unittest.TestCase): offset = elf.GetSymbolFileOffset(fname, ['missing_sym']) self.assertEqual({}, offset)

• def test_read_segments(self):

•    """Test for read_segments()"""
  

•    if not elf.ELF_TOOLS:
  

•        self.skipTest('Python elftools not available')
  

•    fname = self.ElfTestFile('embed_data')
  

•    segments, entry = elf.read_segments(tools.ReadFile(fname))
  

• def test_read_segments_fail(self):

•    """Test for read_segments() without elftools"""
  

•    try:
  

•        old_val = elf.ELF_TOOLS
  

•        elf.ELF_TOOLS = False
  

•        fname = self.ElfTestFile('embed_data')
  

•        with self.assertRaises(ValueError) as e:
  

•            elf.read_segments(tools.ReadFile(fname))
  

•        self.assertIn('Python elftools package is not available',
  

•                      str(e.exception))
  

•    finally:
  

•        elf.ELF_TOOLS = old_val
  

• def test_read_segments_bad_data(self):

•    """Test for read_segments() with an invalid ELF file"""
  

•    fname = self.ElfTestFile('embed_data')
  

•    with self.assertRaises(ValueError) as e:
  

•        elf.read_segments(tools.GetBytes(100, 100))
  

•    self.assertIn('Magic number does not match', str(e.exception))
  

if __name__ == '__main__': unittest.main()