[lldb-dev] When should ArchSpecs match?

[Jason Molenda via lldb-dev]

Oh sorry I missed that.  Yes, I think a value added to the OSType for NoOS or something would work.  We need to standardize on a textual representation for this in a triple string as well, like 'none'.  Then with arm64-- and arm64-*-* as UnknownVendor + UnknownOS we can have these marked as "compatible" with any other value in the case Adrian is looking at.


> On Dec 6, 2018, at 4:05 PM, Zachary Turner <zturner at google.com> wrote:
> 
> 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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