[Lldb-commits] [PATCH] D144528: [lldb] Warn when Mach-O files have overlapping segments

Wed Feb 22 13:20:32 PST 2023

jasonmolenda added a comment.

In D144528#4145610 <https://reviews.llvm.org/D144528#4145610>, @bulbazord wrote:

> In D144528#4145593 <https://reviews.llvm.org/D144528#4145593>, @jasonmolenda wrote:
>
>> 

>> tl;dr it's fine if LINKEDIT's "overlap" because lldb will never need to take an addr_t and figure out which Section it is located in.  (because an addr_t in the LINKEDIT segment of the shared cache would point to EVERY ObjectFile in the shared cache, if it was all reported correctly.)
>>
>> We may find that enabling this warning fires for some unintended situation that we're not looking at right now, but we can re-evaluate if that turns out to be the case.
>
> Out of curiosity, is the scenario you're describing not already handled by `DynamicLoaderDarwin::UpdateImageLoadAddress`? That method specifically checks to see if a section is `__LINKEDIT` to figure out if we should be emitting a warning. Should I be doing the same thing here?

We don't get any new warnings with your patch when it is run against a macOS etc process using a shared cache; it behaves correctly.  The comment in `SectionLoadList::SetSectionLoadAddress` specifically talks about the LINKEDIT case, saying that the DynamicLoader will do the right thing, as you noted.  But it made me try to think through if there might be similar metadata segments that aren't actually loaded in memory, or are inconsequential if they're loaded or not.  We may find when some living on time that there are other cases, but I can't think of them right now - I say give the patch a try.

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https://reviews.llvm.org/D144528