[PATCH] D37520: [ELF] - Fix removing of unused synthetic sections.

[Rui Ueyama via Phabricator via llvm-commits]

ruiu added inline comments.


================
Comment at: ELF/Writer.cpp:1205-1209
+    bool IsEmpty = llvm::all_of(OS->Commands, [](BaseCommand *B) {
+      auto *ISD = dyn_cast<InputSectionDescription>(B);
+      return ISD && ISD->Sections.empty();
+    });
+    if (IsEmpty)
----------------
grimar wrote:
> ruiu wrote:
> > I think I do not understand this code. You don't need to use all_of, right? The only way in which OS becomes empty is (1) it contains only one InputSectionDescription and (2) that InputSectionDescription is empty, no?
> No. If OS has 2 or more ISDs which are empty, it is also empty.
> For example in script from testcase we have ".got  : { *(.got) *(.got) }",
> which means we have OS `.got` and 2 ISDs, one has input section and one is empty from start.
> When we remove unused input section from first ISD it becomes empty, and we want to remove whole OS.
> For that we have to check if all ISDs are empty.
So you are saying that .got output section is not created for `.got : { *(.got) }`  if .got synthetic input section is empty, that is what I expected.

But what about some output section .foo where it is created as `.foo : { *(.bar) }`, if no input file have .bar section? Do we still create .foo?

If yes, that behavior is inconsistent.

If no, there must be a place we remove empty output sections. Doing the same thing here doesn't make sense.


https://reviews.llvm.org/D37520