Accept populated COFF symbol headers

[daladim]

Some binaries (not sure what toolchain has generated them) may have pointers to COFF symbols that point to nothing.
Since COFF symbols tables are deprecated anyway, it could be better to ignore these symbols than returning an Err that will prevent the whole PE file from parsing.

I know you're not always happy to remove error conditions for the sake of parsing more binaries, so I'd like to have your opinion on such a "fix" :-)

Example of such binaries: git for Windows (at least some builds).

• Download PortableGit-2.29.2.3-64-bit.7z.exe from their release page
• Run it so that it extracts itself
• The file at PortableGit\cmd\git.exe has populated pointer_to_symbol_table and number_of_symbols that point after the end of file. Hence, it cannot be parsed by object because of "Invalid COFF symbol table offset or size"

[philipc]

I think this error should be ignored in PeFile::parse instead, since this is only deprecated for PE, not COFF. This also allows someone to still detect this error for PE if desired by parsing the symbol table themselves, outside of PeFile.

This kind of error handling is a reason why PeFile::parse should do as little as possible.

[daladim]

OK, I have pushed a new proposal, that intercepts the error in PeFile::parse instead.

Not sure why adding a #[derive(Default)] on top of struct SymbolTable failed with the error below, so I implemented Default myself.

Compiler error

error[E0599]: the method `unwrap_or_default` exists for enum `core::result::Result<coff::symbol::SymbolTable<'_, R>, read::Error>`, but its trait bounds were not satisfied
  --> src/read/pe/file.rs:60:39
   |
60 |                   symbols: coff_symbols.unwrap_or_default(),
   |                                         ^^^^^^^^^^^^^^^^^ method cannot be called on `core::result::Result<coff::symbol::SymbolTable<'_, R>, read::Error>` due to unsatisfied trait bounds
   | 
  ::: src/read/coff/symbol.rs:20:1
   |
20 | / pub struct SymbolTable<'data, R = &'data [u8]>
21 | | where
22 | |     R: ReadRef<'data>,
23 | | {
24 | |     symbols: &'data [pe::ImageSymbolBytes],
25 | |     strings: StringTable<'data, R>,
26 | | }
   | |_- doesn't satisfy `coff::symbol::SymbolTable<'_, R>: Default`
   |
   = note: the following trait bounds were not satisfied:
           `coff::symbol::SymbolTable<'_, R>: Default`

[philipc]

Thanks!

derive can sometimes add unnecessary trait bounds. I didn't investigate, but I assume that is happening here.