[libre-riscv-dev] offtopic: memory safety

Luke Kenneth Casson Leighton lkcl at lkcl.net
Thu Jul 18 06:25:01 BST 2019

On Wed, Jul 17, 2019 at 10:41 PM Jacob Lifshay <programmerjake at gmail.com> wrote:

>  of even deeper concern is that they're used to justify one language
> > over another for completely inappropriate purposes.
> >
> yeah. though it is nice to have a programming language that is designed to
> help you avoid UB, without needing extensive experience to get it right --
> such as Rust (just don't use the unsafe kw), Python, Java, and others.

agreed.  what will make me feel more comfortable about rust is when
(if) it stabilises enough for the gcc team to create a frontend for it
(like the fortran and java frontends, which some people aren't aware
these exist).

cutting out the llvm JIT intermediary and having the actual compiler
directly generate the assembler would alleviate some potential
security / safety concerns.  i'm much happier trusting something where
there's less "pieces in the puzzle" basically.

> C (and C++) is powerful, but it's easy to mess up without extensive
> experience -- I've worked on commercial production firmware where all the
> non-reenterant file system code was called from the USB interrupt without
> any kind of mutex, disabling interrupts elsewhere, or similar. that same
> codebase used global variables modified by interrupts without using
> volatile (pretty much the one spot other than memory-mapped hw where
> volatile is the correct tool). They relied on optimizations not being ran.
> I've even seen code that uses memset to initialize std::string after
> running the constructor!

i must have just totally lucked out with my choices of places to work
at.  the first one was CEDAR Audio (real-time audio restoration),
where they were doing TI (50MFLOP) DSP programming and had created
their own mixed c++ and x86 assembler GUI that ran on top of DOS, and
did its own INT33 handling, direct AT/XT bus assembly programming (to
communicate with the DSP card), wrote direct to the VGA screen and so

we created our own version of the Win16/32 "Message Passing" stack but
added priorities to it.  there was a separate message-stack for
interrupts and we had to implement context-switching (in x86
assembler).  it worked extremely well, and even on 386sx16 machines
the GUI was responsive and efficient.

then i went to work for Pi Technology in Milton, and there they
successfully adopted ISO9001 (BS5750).  why was it successful (and
liked)? because they were already doing *five* man line-by-line
code-reviews on the firmware that was to run in Engine Controllers
(get that wrong and it could kill someone), and they already *had*
coding standards that said "on no account use malloc or free in c++"
and other extremely sensible things that everyone knew, understood
*and respected*.

so when i heard of how ISO9001 was quotes universally hated quotes i
was seriously taken aback.

and i hear horror stories like the one you tell above, and it just...
i genuinely don't understand how people manage to get themselves into
such holes.

> >  in the case of the samba team "leaders", they simply genuinely had no
> > idea - and no respect for - the dual nature of the two OSes that they
> > were working with (windows *and* unix).  it was too much for them, and
> > they made - repeatedly - poor design choices as a result.
> >
> hopefully they've been refactored since then.

mmm.... no.  they basically went down the rabbit hole of recreating
openldap *and* heimdal, both of which are well over a quarter of a
million lines of code, each, with really experienced *separate* teams
behind each, and, with no other wider user-adoption, make them the
sole exclusive maintainer of something that's not in the slightest bit
config-compatible with either project.

[NT 5 aka Windows 2000 adopted LDAP and Kerberos, then broke both by
f*****g about with the standards.  luke howard wrote some extremely
simple patches to both OpenLDAP and Heimdal, and developed a complete
Active Directory replacement called XAD in about 2 years flat.  it was
*eventually* bought by Novell].

> In the mean time, one can vainly hope that microsoft switches windows to
> using unix and deprecates the weirder parts of win32 -- apple did when they
> introduced OS X.

yyeah, they're an "interesting" company.  they can't do that - they
have to support their customers.  there's even switches inside DOS
CMD.EXE which say "if executable == SIMCITY.EXE enable deliberate
malloc memory bug".

no, really, not kidding, look it up!

there's been an internal fight for decades, of two teams that want to
make a *deliberate* incompatibility "clean sweep", to clear away the
awful cruft that keeps older applications running, and those who say,
"sorry, the customer comes first: legacy is king".


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