Re: [PATCH 4/7] Add sniffer for Cygwin x86_64 core dumps

[Jon Turney <jon.turney@dronecode.org.uk>]

On 03/07/2020 00:59, Simon Marchi wrote:
>> @@ -1276,6 +1278,24 @@ amd64_windows_osabi_sniffer (bfd *abfd)
>>     return GDB_OSABI_WINDOWS;
>>   }
>>   
>> +static enum gdb_osabi
>> +amd64_cygwin_core_osabi_sniffer (bfd *abfd)
>> +{
>> +  const char *target_name = bfd_get_target (abfd);
>> +
>> +  /* Cygwin uses elf core dumps.  Do not claim all ELF executables,
>> +     check whether there is a .reg section of proper size.  */
>> +  if (strcmp (target_name, "elf64-x86-64") == 0)
>> +    {
>> +      asection *section = bfd_get_section_by_name (abfd, ".reg");
>> +      if (section != nullptr
>> +	  && bfd_section_size (section) == AMD64_WINDOWS_SIZEOF_GREGSET)
>> +	return GDB_OSABI_CYGWIN;
>> +    }
>> +
>> +  return GDB_OSABI_UNKNOWN;
> 
> The obvious question here is, what happens if we are loading the core for
> another architecture, and it happens by bad luck that the .reg section is
> of that size, even though it's not a Cygwin core.  Will this give a false
> positive?

It would seem to.

> I presume that since this is copied on the i386, that discussion already
> happened in the past for i386, and it was concluded that there was no better
> way to identify a Cygwin core.  But I thought I'd ask just to be sure.

idk.  The x86 Cygwin core dump support was added in 2000 (see commit 
16e9c715dffb96efda481dc20cdb5bb6fbde0dff), when I was blissfully 
ignorant of all this nonsense :).

It certainly would be possible to improve this by checking if the ELF 
file contains a note of type NT_WIN32PSTATUS, but I'm not sure how we 
might do that here.