RFC: libiberty PATCH to disable demangling of ancient mangling schemes

Pedro Alves palves@redhat.com
Fri Dec 7 16:11:00 GMT 2018

Adding gdb-patches, since demangling affects gdb.

Ref: https://gcc.gnu.org/ml/gcc-patches/2018-12/msg00407.html

On 12/07/2018 10:40 AM, Jakub Jelinek wrote:
> On Fri, Dec 07, 2018 at 10:27:17AM +0000, Nick Clifton wrote:
>>>> Looks good to me.  Independently, do you see a reason not to disable the
>>>> old demangler entirely?
>>> Like so.  Does anyone object to this?  These mangling schemes haven't
>>> been relevant in decades.
>> I am not really familiar with this old scheme, so please excuse my ignorance
>> in asking these questions:
>>   * How likely is it that there are old toolchain in use out there that still 
>>     use the v2 mangling ?  Ie I guess that I am asking "which generation(s)
>>     of gcc used v2 mangling ?"
> GCC 3.0 and up used the new (Itanium C++ ABI) mangling, 2.95 and older used the old
> mangling (2.96-RH used the new mangling I believe).
> So you need compiler older than 17.5 years to have the old mangling.
> Such a compiler didn't support most of the contemporarily used platforms
> though at all (e.g. x86-64, powerpc64le, aarch64, I believe not even
> powerpc64-linux).

I guess the question would be whether it is reasonable to expect
that people will still need to debug&inspect (with gdb, c++filt, etc.)
any such old binary, and that they will need to do it with with modern
tools, as opposed to sticking with older binutils&gdb, and how often
would that be needed.

I would say that it's very, very unlikely, and not worth it of the
maintenance burden.

Last I heard of 2.95-produced binaries I think was for some ancient gcc-2.95-based
cross compiler that was still being minimally maintained, because it was needed
to build&maintain some legacy stuff.  That was maybe over 8 years ago, and
it was off trunk.  It's probably dead by now.  And if isn't dead,
whoever maintains the compiler off trunk certainly can also maintain old-ish
binutils & gdb off trunk.

Pedro Alves

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