On Mon, May 20, 2024 at 9:17 AM Douglas McIlroy <
douglas.mcilroy@dartmouth.edu> wrote:

> I'm surprised by nonchalance about bad inputs evoking bad program
> behavior. That attitude may have been excusable 50 years ago. By now,
> though, we have seen so much malicious exploitation of open avenues of
> "undefined behavior" that we can no longer ignore bugs that "can't happen
> when using the tool correctly". Mature software should not brook incorrect
> usage.
>
> Accepting bad inputs can also lead to security issues.  The data breaches
from SQL-based attacks are a modern case in point.

IMO, as a programmer you owe it to your users to do your best to detect bad
input and to handle it in a graceful fashion.  Nothing is more frustrating
to a user than to have a program blow up in their face with a seg fault, or
even worse, simply exit silently.

As the DEC compiler team's expert on object files, I was called on to add
object file support to a compiler back end originally targeted to VMS
only.  I inherited support of the object file generator for Unix COFF and
later wrote the support for Microsoft PECOFF and ELF.  When our group was
bought by Intel I did the object file support for Apple OS X MACH-O in the
Intel compiler back end.

I found that the folks who write linkers are particularly lazy about error
checking and error handling.  They assume that the compiler always
generates clean object files.  That's OK I suppose if the compiler and
linker people are in the same organization.  If the linker falls over you
can just go down the hall and have the linker developer debug the issue and
tell you where you went wrong.  But that doesn't work when they work for
different companies and the compiler person doesn't have access to the
linker sources.  I ran into a lot of cases where my buggy object file
caused the linker to seg fault or, even worse, simply exit without an error
message.

I ended up writing a very thorough formatted dumper for each object file
format that did very thorough checking for proper syntax and as many
semantic errors (e.g., symbol table index number out of range) as I could.

-Paul W.