[llvm-dev] Need help with code generation

[Rui Ueyama via llvm-dev]

On Mon, Mar 21, 2016 at 10:49 PM, David Blaikie via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

>
>
> 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.
>

I think this is the same from the user's point of view. If LLVM is not
crash-bug-free in the version you are using, you need some precaution such
as forking in order to protect your program from crashing if you need 100%
guarantee.


> - Dave
>
>
>>
>> Cheers,
>> Rafael
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>> llvm-dev at lists.llvm.org
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>>
>
>
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