Re: git: 4617a6cb82a6 - main - nlist: Handle multiple symbol tables

On Sat, Aug 29, 2026 at 01:07:44PM -0400, John Baldwin wrote:
> On 8/28/26 14:30, Dag-Erling Smørgrav wrote:
> > John Baldwin <jhb@FreeBSD.org> writes:
> > > The _Foo vs Foo change broke many uses of kvm_nlist in the tree.  In
> > > particular, ktrdump no longer works on crashdumps now, and I finally
> > > single-stepped through it today to figure out why.
> > > 
> > > A quick grep shows me all these places that are now broken:
> > > [...]
> > > Would you rather revert the underscore change or fix all these?
> > 
> > Looks to me like they were all incorrect to begin with and only worked
> > because of the hack in nlist(), so I would vote for fixing the calls.
> > But perhaps kib@ should weigh in since he was the one who suggested
> > dropping the hack.
> > 
> > Cc: to re@ as this is a regression in 14.5.
> 
> I think a.out required the leading underscore, so when many of these
> were originally added they were in fact correct, and the hack was
> required to allow libkvm to work across both a.out and ELF.  It may
> very well be that we no longer care about a.out, but this should be
> an intentional decision if so.  It is (almost) an ABI change in the
> sense that it changes the original API contract.

Yes I am sure that this was a transitional measure to allow the same
code to uniformly handle both a.out (with underscores) and ELF
(without) names.  But in the ELF times, the mis-feature does not allow
to distinguish symbol and _symbol.

It can be considered an ABI change, but IMO the behavior is too confusing
to be useful for anything except the wrong code, as des noted.