[PATCH] D28612: [ELF] - Added support for --emit-relocs.

[George Rimar via Phabricator via llvm-commits]

grimar added inline comments.


================
Comment at: ELF/InputFiles.cpp:409
+      if (!isa<InputSection<ELFT>>(Target))
+        fatal(toString(this) + ": --emit-relocs for relocations sections "
+                               "pointing to .eh_frame is not supported");
----------------
ruiu wrote:
> grimar wrote:
> > I am going to remove that fatal error in following patch.
> > It is needed for linux kernel, but since it involves move DependentSection from InputSection<ELFT> to somewhere and also adding more additional tests probably, I think it is better not to do that change in this patch.
> > Hope it's ok.
>  I think what you really need to do is to make it a vector just like Rafael did in https://reviews.llvm.org/D28626.
I do not see how vector helps. Issue here is that

DependentSection is a member of InputSection, but
EhInputSection inhireted from InputSectionBase<ELFT>

```
EhInputSection : public InputSectionBase<ELFT>
```

In following patch I plan to move DependentSection to InputSectionBase probably to solve that problem.


================
Comment at: ELF/LinkerScript.cpp:265-270
+
+    // If we discard a section, we also should discard a dependent section.
+    InputSection<ELFT> *IS = dyn_cast<InputSection<ELFT>>(S);
+    if (!IS || !IS->DependentSection || !IS->DependentSection->Live)
+      continue;
+    discard({IS->DependentSection});
----------------
ruiu wrote:
> I don't think this is correct. You shouldn't add any code this function, or there's a bug in GC.
> 
> If section S depends on section T, and if S is marked as dead, T must be marked as dead too before the control reaches this function. So both S and T will be discarded without doing anything special.
It is not relative to GC at all.
Please look at emit-reloc-discard.s.

Call is:
```
# RUN: echo "SECTIONS { /DISCARD/ : { *(.debug*) } }" > %t.script
# RUN: ld.lld --emit-relocs --script %t.script %t.o -o %t1
```

So .debug_* sections are discarded **from script**, GC is not involved and not executed.
And since .debug_ are discarded, .rela.debug_* should be discarded as well. That is what that place do.


https://reviews.llvm.org/D28612