22 Aug
2018
22 Aug
'18
9:46 p.m.
On Wed, 22 Aug 2018 11:29:40 -0400 Paul Winalski
<paul.winalski(a)gmail.com> wrote:
On 8/22/18, Perry E. Metzger
<perry(a)piermont.com> wrote:
Not necessarily. One could produce a language-independent way of
signaling what the type signatures are (perhaps with normalized
language-dependent strings) and the linker could just check that they
match.
I've seen several languages (like OCaml) hack around the lack of this
by providing an auxiliary file for a pre-link phase to check off
of. It would be nicer if the linker could just handle that.
And, as I noted, this would doubtless prevent a _lot_ of bugs.
One could simply decorate the symbols with a
(language, semi-opaque "type string") pair, and the linker could just
verify that they matched without understanding semantics.
To my knowledge, object file formats still don't have information
about type signatures, and linkers still don't care about types.
This is actually a problem. It would probably prevent a lot of
errors if those things changed.
For a linker to enforce (or warn about) type and call signature
matching, it would have to know the type and call semantics of each
particular language, Not impossible, but a difficult and cumbersome
problem, particularly
as language and compiler implementation semantics vary over time.
As I noted, there are ways to get around that.
C++ and other strongly-typed languages typically hack
around the
problem using name decoration. Not elegant, but effective.
Name mangling for C++ is needed for another reason, too, which is that
a single "name" foo might be multiple different concrete functions
depending on what type it is invoked on.
Has anyone experimented with building Unix using C++,
to take
advantage of strong typing? My guess is no--it would be a Herculean
task likely to introduce more bugs than it would fix.
C++ doesn't have strong typing in the modern sense. It also has some
small incompatibilities with C's syntax and semantics, sufficient that
you can't just (say) compile the Linux kernel with a C++ compiler and
have it work.
Perry
--
Perry E. Metzger perry(a)piermont.com