[lldb-dev] When should ArchSpecs match?

[Zachary Turner via lldb-dev]

That's what I mean though, perhaps we could add a value to the OSType
enumeration like BareMetal or None to explicitly represent this.  the
SubArchType enum has NoSubArch, so it's not without precedent.  As long as
you can express it in the triple format, the problem goes away.

On Thu, Dec 6, 2018 at 3:55 PM Jason Molenda <jmolenda at apple.com> wrote:

> There is genuinely no OS in some cases, like people who debug the software
> that runs in a keyboard or a mouse.  And to higher-level coprocessors in a
> modern phones; the SOCs on all these devices have a cluster of processors,
> and only some of them are running an identifiable operating system, like
> iOS or Android.
>
> I'll be honest, it's not often that we'll be debugging an arm64-apple-none
> target and have to decide whether an arm64-apple-ios binary should be
> loaded or not.  But we need some way to express this kind of environment.
>
>
> > On Dec 6, 2018, at 3:50 PM, Zachary Turner <zturner at google.com> wrote:
> >
> > Is there some reason we can’t define vendors, environments, arches, and
> oses for all supported use cases? That way “there is no os” would not ever
> be a thing.
> > On Thu, Dec 6, 2018 at 3:37 PM Jason Molenda via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
> > I think the confusing thing is when "unspecified" means "there is no OS"
> or "there is no vendor" versus "vendor/OS is unspecified".
> >
> > Imagine debugging a firmware environment where we have a cpu arch, and
> we may have a vendor, but we specifically do not have an OS.  Say
> armv7-apple-none (I make up "none", I don't think that's valid).  If lldb
> is looking for a binary and it finds one with armv7-apple-ios, it should
> reject that binary, they are incompatible.
> >
> > As opposed to a triple of "armv7-*-*" saying "I know this is an armv7
> system target, but I don't know anything about the vendor or the OS" in
> which case an armv7-apple-ios binary is compatible.
> >
> > My naive reading of "arm64-*-*" means vendor & OS are unspecified and
> should match anything.
> >
> > My naive reading of "arm64" is that it is the same as "arm64-*-*".
> >
> > I don't know what a triple string looks like where we specify "none" for
> a field.  Is it armv7-apple-- ?  I know Triple has Unknown enums, but
> "Unknown" is ambiguous between "I don't know it yet" versus "It not any
> Vendor/OS".
> >
> > Some of the confusion is the textual representation of the triples, some
> of it is the llvm Triple class not having a way to express (afaik) "do not
> match this field against anything" aka "none".
> >
> >
> >
> > > On Dec 6, 2018, at 3:19 PM, Adrian Prantl via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
> > >
> > > I was puzzled by the behavior of ArchSpec::IsExactMatch() and
> IsCompatibleMatch() yesterday, so I created a couple of unit tests to
> document the current behavior. Most of the tests make perfect sense, but a
> few edge cases really don't behave like I would have expected them to.
> > >
> > >>  {
> > >>    ArchSpec A("arm64-*-*");
> > >>    ArchSpec B("arm64-apple-ios");
> > >>    ASSERT_FALSE(A.IsExactMatch(B));
> > >>    // FIXME: This looks unintuitive and we should investigate whether
> > >>    // this is the desired behavior.
> > >>    ASSERT_FALSE(A.IsCompatibleMatch(B));
> > >>  }
> > >>  {
> > >>    ArchSpec A("x86_64-*-*");
> > >>    ArchSpec B("x86_64-apple-ios-simulator");
> > >>    ASSERT_FALSE(A.IsExactMatch(B));
> > >>    // FIXME: See above, though the extra environment complicates
> things.
> > >>    ASSERT_FALSE(A.IsCompatibleMatch(B));
> > >>  }
> > >>  {
> > >>    ArchSpec A("x86_64");
> > >>    ArchSpec B("x86_64-apple-macosx10.14");
> > >>    // FIXME: The exact match also looks unintuitive.
> > >>    ASSERT_TRUE(A.IsExactMatch(B));
> > >>    ASSERT_TRUE(A.IsCompatibleMatch(B));
> > >>  }
> > >>
> > >
> > > Particularly, I believe that:
> > > - ArchSpec("x86_64-*-*") and ArchSpec("x86_64") should behave the same.
> > > - ArchSpec("x86_64").IsExactMatch("x86_64-apple-macosx10.14") should
> be false.
> > > - ArchSpec("x86_64-*-*").IsCompatibleMath("x86_64-apple-macosx")
> should be true.
> > >
> > > Does anyone disagree with any of these statements?
> > >
> > > I fully understand that changing any of these behaviors will
> undoubtedly break one or the other edge case, but I think it would be
> important to build on a foundation that actually makes sense if we want to
> be able to reason about the architecture matching logic at all.
> > >
> > > let me know what you think!
> > > -- adrian
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