[PATCH] D67761: [ELF] Error if the linked-to section of a SHF_LINK_ORDER section is discarded

[Fangrui Song via Phabricator via llvm-commits]

MaskRay marked an inline comment as done.
MaskRay added inline comments.


================
Comment at: ELF/Writer.cpp:1527
+              toString(link));
+    }
+    if (errorCount())
----------------
grimar wrote:
> Should we report this much earlier, on GC stage, in MarkLive.cpp for example?
> 
> I do not have a chance to check it today unfortunately, but looks it could be done somewhere here:
> 
> ```
>   // Report garbage-collected sections.
>   if (config->printGcSections)
>     for (InputSectionBase *sec : inputSections)
>       if (!sec->isLive())
>         message("removing unused section " + toString(sec));
> ```
> 
> ?
markLive() is called before processSectionCommands(). Before processSectionCommands(), output sections are not allocated, and the `link->getParent()` check does not work.

We can change `link->getParent()` to `link->isLive()` if we really want to perform the check in markLive(). However, we have another rule: /DISCARD/ discards an input section as well as its dependentSections. If sh_link(a)=b && a has SHF_LINK_ORDER, we currently place a in b's dependentSections list. If we discard b, a will be discarded as well (see discard-section-metadata.s). Having the check in markLive() would issue a premature error.

For the reasons above, we cannot perform the check in markLive().

Actually, I'm thinking if we can/should drop the rule:

> If sh_link(a)=b && a has SHF_LINK_ORDER, we currently place a in b's dependentSections list

I need to check for tests and previous commits on this.


Repository:
  rLLD LLVM Linker

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  https://reviews.llvm.org/D67761/new/

https://reviews.llvm.org/D67761