Clear output section from linker script command when it's removed.

[dmikulin]

Summary

This is an attempt to fix https://bugs.llvm.org/show_bug.cgi?id=33029.
When output sections are removed, the need to be purged from linker script commands that define them.

[dmikulin]

Updated diff to address comments from the review and the online discussion.

[ruiu]

ELF/LinkerScript.cpp

700

What is the meaning of this change?

[dmikulin]

ELF/LinkerScript.cpp

700

Rafael suggested that we should not be tracking section types of previous sections and always use PROGBITS for dummy sections.

[dmikulin]

Removed Writer.cpp changes.

ELF/LinkerScript.cpp

 }
 
 void LinkerScript::adjustSectionsBeforeSorting() {
   // If the output section contains only symbol assignments, create a
   // corresponding output section. The bfd linker seems to only create them if
   // '.' is assigned to, but creating these section should not have any bad
   // consequeces and gives us a section to put the symbol in.
   uint64_t Flags = SHF_ALLOC;
-  uint32_t Type = SHT_PROGBITS;
 
   for (int I = 0, E = Opt.Commands.size(); I != E; ++I) {
     auto *Cmd = dyn_cast<OutputSectionCommand>(Opt.Commands[I]);
     if (!Cmd)
       continue;
     if (OutputSection *Sec = Cmd->Sec) {
       Flags = Sec->Flags;
-      Type = Sec->Type;
       continue;
     }
 
     if (isAllSectionDescription(*Cmd))
       continue;
 
-    auto *OutSec = make<OutputSection>(Cmd->Name, Type, Flags);
+    auto *OutSec = make<OutputSection>(Cmd->Name, SHT_PROGBITS, Flags);
     OutSec->SectionIndex = I;
     OutputSections->push_back(OutSec);
     Cmd->Sec = OutSec;
     SecToCommand[OutSec] = Cmd;
   }
 }
 
 void LinkerScript::adjustSectionsAfterSorting() {

test/ELF/linkerscript/arm-lscript.s

+// REQUIRES: arm
+// RUN: llvm-mc -filetype=obj -triple=armv7a-none-linux-gnueabi %s -o %t.o
+// RUN: echo  "SECTIONS { \
+// RUN:         .rel.dyn : {    } \
+// RUN:         .zed     : { PROVIDE_HIDDEN (foobar = .); } \
+// RUN:         }" > %t.script
+// This is a test case for PR33029. Making sure that linker can digest
+// the above script without dumping core.
+// RUN: ld.lld -emit-relocs -T %t.script %t.o -shared -o %t.so