Re: [Patch]: ld crash on i386/pe when linking with a dll that has no exports

[Dave Korn <dave dot korn dot cygwin at googlemail dot com>]

Christopher Faylor wrote:
> On Wed, Nov 25, 2009 at 10:20:54AM +0100, Tristan Gingold wrote:
>> Hi,
>>
>> we got a crash when linking with a dll whose export directory is empty:
>> ...
>> NumberOfRvaAndSizes	00000010
>>
>> The Data Directory
>> Entry 0 00000000 00000000 Export Directory [.edata (or where ever we found it)]
>> Entry 1 00016000 0000003c Import Directory [parts of .idata]
>> ...
>>
>> In fact there is no guard against such values in ld/pe-dll.c(pe_implied_import_dll) and this function
>> assumes that the export directory entry is not empty if present.
>>
>> This patch fixes this crash.
> 
> Isn't this supposed to be handled by the
> 
>   if (num_entries < 1) /* No exports.  */
>     return FALSE;
> 
> a few lines above it?
> 
> If this test is inadequate then it seems like num_entries isn't needed
> and should be deleted.

  Nope, that's a misunderstanding of the meaning of num_entries (which I also
made, until I went back and checked the spec).  The NumberOfRvaAndSizes value
is the count of filled-out entries in the IMAGE_DATA_DIRECTORY array, so this
is just checking that entry #0 (.edata size and offset) is even present; then
it goes on to look at the data pointed to by that entry, without noticing that
despite being filled out, it might be filled out with null values.  The order
of data directory entries is fixed, so you have to have a null export table
entry if you want to be able to put anything in the subsequent import table entry.

  Linking against a DLL with zero exports may be kind of pointless, but it
should at least work!  The patch is OK, thank you Tristan :)

    cheers,
      DaveK