bug#27527: 25.2; start-process crash on Windows with 64bit .NET executable

["Saulius Menkevičius" <saulius.menkevicius@gmail.com>]

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Sure,

Here it is:

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diff --git a/src/w32proc.c b/src/w32proc.c
index 200c2b2ba4..2d303e9139 100644
--- a/src/w32proc.c
+++ b/src/w32proc.c
@@ -1618,6 +1618,10 @@ w32_executable_type (char * filename,
               /* Look for Cygwin DLL in the DLL import list. */
               IMAGE_DATA_DIRECTORY import_dir =
                 data_dir[IMAGE_DIRECTORY_ENTRY_IMPORT];
+
+	      /* Import directory can be missing on .NET dlls */
+	      if (import_dir.VirtualAddress != 0)
+                {
                   IMAGE_IMPORT_DESCRIPTOR * imports =
                     RVA_TO_PTR (import_dir.VirtualAddress,
                                 rva_to_section (import_dir.VirtualAddress,
@@ -1653,6 +1657,7 @@ w32_executable_type (char * filename,
                 }
             }
   	}
+    }
 
 unwind:
   close_file_data (&executable);

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> Am 29.06.2017 um 17:24 schrieb Eli Zaretskii <eliz@gnu.org>:
> 
>> From: Saulius Menkevičius <saulius.menkevicius@gmail.com>
>> Date: Thu, 29 Jun 2017 12:41:55 +0300
>> 
>> The issue was encountered when debugging a problem with omnisharp-emacs
>> package where starting a server process (written for and running in a  .NET/CLR VM)
>> crashes emacs with a segfault.
>> 
>> Recompiling with -g -O0 has revealed a problem in implementation of
>> w32_executable_type in src/w32proc.c where the code is attempting to list
>> DLL imports in a binary but the import table points to NULL. This code works for
>> .NET binaries compiled for x86 so the problem is specific to 64 bit Windows / .NET DLLs.
>> 
>> The callstack of a crash is below and I have a patch attached that fixes the problem. 
>> The patch applies cleanly to both master and emacs-25 branches.
> 
> Thanks.
> 
> Can you send the diffs generated with the -b switch?  I think all you
> did was to condition the use of the import directory on its being
> non-NULL, but it's hard to tell judging just by the diffs you posted.