[llvm-dev] Need help with code generation

[David Blaikie via llvm-dev]

On Mon, Mar 21, 2016 at 2:46 PM, Rafael Espíndola <llvm-dev at lists.llvm.org>
wrote:

> On 21 March 2016 at 17:34, Tim Northover via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> >> My understanding is that clang and llvm themselves are designed this way
> >> (crash when the unexpected happens).
> >
> > I don't think so. I'd view any Clang crash as a bug (probably to be
> > prioritised below silent CodeGen and many others, but not "working as
> > designed").
> >
> >> For example the fact that clang forks itself to be able to report
> diagnostics
> >
> > That seems like just trying to make our own job easier to me. I think
> > the entire point of the fork is to get a backtrace we can fix, and
> > point out where the user should send it.
> >
> >> llvm is full of report_fatal_error() (or worse, assertions that can
> fire on unexpected user input).
> >
> > A bit of a grey area since LLVM isn't itself a user-facing tool, but I
> > think I'd still say that a report_fatal_error that's not actionable by
> > the user is actually an LLVM bug. And a segfault definitely so.
>
> It is completely trivial to crash llvm. A case I wrote today in
> another thread while waiting for tests to run:
>
> target triple = "x86_64-unknown-linux-gnu"
> @".data" = global i32 42
>
> That will crash "llc -filetype=obj". The fact that it is considered a
> bug doesn't mean much if there is no coordinated effort to fix them.
>

I think it does, actually - that patches will be accepted to fix pretty
much any crash in LLVM. (llc isn't a user facing tool, so that's a
praticularly low priority - but as a general library (I assume your example
also crashes Clang, which would be where this would surface in a more
important way) it's pretty well accepted that crashes are bugs, I think)


> Right now lld is already harder to crash than llvm. We are just being
> honest about the fact that it is possible to craft a .o file that will
> crash it.
>

But the difference seems to be you know about these cases and don't
consider them to be bugs/anything to fix. In LLVM if they're known, they're
at least considered bugs and often/usually considered by someone to be
worth fixing at some point.

- Dave


>
> Cheers,
> Rafael
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160321/09347234/attachment.html>