[ELF] - Linkerscript: support combination of linkerscript and --compress-debug-sections.

Previously it was impossible to use linkerscript with --compress-debug-sections 
because of assert failture:
Assertion failed: isFinalized(), file C:\llvm\lib\MC\StringTableBuilder.cpp, line 64

Patch fixes the issue

llvm-svn: 302413

lld/ELF/LinkerScript.cpp

@@ -406,15 +406,8 @@ void LinkerScript::processCommands(OutputSectionFactory &Factory) {
       }
 
       // Add input sections to an output section.
-      unsigned Pos = 0;
-      for (InputSectionBase *S : V) {
-        // The actual offset will be computed during
-        // assignAddresses. For now, use the index as a very crude
-        // approximation so that it is at least easy for other code to
-        // know the section order.
-        cast<InputSection>(S)->OutSecOff = Pos++;
+      for (InputSectionBase *S : V)
         Factory.addInputSec(S, Cmd->Name, Cmd->Sec);
-      }
       if (OutputSection *Sec = Cmd->Sec) {
         assert(Sec->SectionIndex == INT_MAX);
         Sec->SectionIndex = I;
@@ -648,6 +641,11 @@ void LinkerScript::assignOffsets(OutputSectionCommand *Cmd) {
     Dot = CurMemRegion->Offset;
   switchTo(Sec);
 
+  // We do not support custom layout for compressed debug sectons.
+  // At this point we already know their size and have compressed content.
+  if (CurOutSec->Flags & SHF_COMPRESSED)
+    return;
+
   for (BaseCommand *C : Cmd->Commands)
     process(*C);
 }

lld/ELF/OutputSections.cpp

@@ -140,12 +140,24 @@ template <class ELFT> void OutputSection::finalize() {
   this->Info = S->OutSec->SectionIndex;
 }
 
+static uint64_t updateOffset(uint64_t Off, InputSection *S) {
+  Off = alignTo(Off, S->Alignment);
+  S->OutSecOff = Off;
+  return Off + S->getSize();
+}
+
 void OutputSection::addSection(InputSection *S) {
   assert(S->Live);
   Sections.push_back(S);
   S->OutSec = this;
   this->updateAlignment(S->Alignment);
 
+  // The actual offsets will be computed by assignAddresses. For now, use
+  // crude approximation so that it is at least easy for other code to know the
+  // section order. It is also used to calculate the output section size early
+  // for compressed debug sections.
+  this->Size = updateOffset(Size, S);
+
   // If this section contains a table of fixed-size entries, sh_entsize
   // holds the element size. Consequently, if this contains two or more
   // input sections, all of them must have the same sh_entsize. However,
@@ -160,11 +172,8 @@ void OutputSection::addSection(InputSection *S) {
 // and scan relocations to setup sections' offsets.
 void OutputSection::assignOffsets() {
   uint64_t Off = 0;
-  for (InputSection *S : Sections) {
-    Off = alignTo(Off, S->Alignment);
-    S->OutSecOff = Off;
-    Off += S->getSize();
-  }
+  for (InputSection *S : Sections)
+    Off = updateOffset(Off, S);
   this->Size = Off;
 }
 

lld/test/ELF/linkerscript/Inputs/compress-debug-sections.s

@@ -0,0 +1,3 @@
+.section .debug_str
+  .asciz "CCC"
+  .asciz "DDD"

lld/test/ELF/linkerscript/compress-debug-sections.s

@@ -0,0 +1,36 @@
+# REQUIRES: x86, zlib
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux \
+# RUN:   %S/Inputs/compress-debug-sections.s -o %t1.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t2.o
+
+## .debug_str section is mergeable. LLD would combine all of them into single
+## mergeable synthetic section. We use -O0 here to disable merging, that
+## allows to check that input sections has correctly assigned offsets.
+
+# RUN: echo "SECTIONS { }" > %t.script
+# RUN: ld.lld -O0 %t1.o %t2.o %t.script -o %t1 --compress-debug-sections=zlib
+# RUN: llvm-dwarfdump %t1 | FileCheck %s
+# RUN: llvm-readobj -s %t1 | FileCheck %s --check-prefix=ZLIBFLAGS
+
+# RUN: echo "SECTIONS { .debug_str 0 : { *(.debug_str) } }" > %t2.script
+# RUN: ld.lld -O0 %t1.o %t2.o %t2.script -o %t2 --compress-debug-sections=zlib
+# RUN: llvm-dwarfdump %t2 | FileCheck %s
+# RUN: llvm-readobj -s %t2 | FileCheck %s --check-prefix=ZLIBFLAGS
+
+# CHECK:       .debug_str contents:
+# CHECK-NEXT:    CCC
+# CHECK-NEXT:    DDD
+# CHECK-NEXT:    AAA
+# CHECK-NEXT:    BBB
+
+# ZLIBFLAGS:       Section {
+# ZLIBFLAGS:         Index:
+# ZLIBFLAGS:         Name: .debug_str
+# ZLIBFLAGS-NEXT:    Type: SHT_PROGBITS
+# ZLIBFLAGS-NEXT:    Flags [
+# ZLIBFLAGS-NEXT:      SHF_COMPRESSED
+
+.section .debug_str
+  .asciz "AAA"
+  .asciz "BBB"