Re: crc32, gpl, debuglink, and interoperability.

[Mark Wielaard <mark@klomp.org>]

Hi David,

On Fri, 2020-10-09 at 13:59 -0700, David Anderson wrote:
> I'm the maintainer of libdwarf and dwarfdump and wish to
> interoperate with gdb/debuglink by reading the appropriate
> sections and validating the crc32 when appropriate.
> 
> The crc32 used in binutils for debuglink is under plain GPLV3.
> Linking to sucn a thing (from what I've been able to find and
> somewhat-understand) means the GPL applies to the linked work.
> That is not appropriate for the libdwarf library.
> 
> So how can I get permission to use LGPL v2.1 (which most of
> libdwarf is) or LGPL v3?  on the relevant crc32 function (in
> bfd/opncls.c)?  In other words extract the source and apply
> an LGPL to the one function calculating the debuglink crc.
> 
> At present interoperability with debuglink is impossible  in
> libdwarf (so impossible in dwarfdump) and I would like to
> make it work.

If you like a dual GPLv2+/LGPLv3+ license better, then you can find an
implementation in elfutils too:
https://sourceware.org/git/?p=elfutils.git;a=blob;f=lib/crc32.c;hb=HEAD

But it is really a fairly standard crc-32. See the end of 
https://www.sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html
 for the polynomial used. You can use that to generate the crc-32
table. Then all you need to know is that you start with 0xFFFFFFFF and
that the CRC is inverted when the calculation is done.

Cheers,

Mark