Set non alloc section address to 0 earlier

[• rafael]

Summary

Currently we do layout as if non alloc sections had an actual address and then set it to zero. This produces a few odd results where a symbol has an address that is inconsistent with the section address.

The simplest way to fix it is probably to just set the address earlier.

The behavior of bfd seems to be similar, but it only sets the non alloc section address if the section is missing from the linker script or if the script has an explicit " : 0" setting the address of the output section (which the default script does).

[ruiu]

LGTM

[• espindola]

r305323

ELF/LinkerScript.cpp

if (!Cmd->Sym)
     return;
 
   auto *Sym = cast<DefinedRegular>(Cmd->Sym);
   ExprValue V = Cmd->Expression();
   if (V.isAbsolute()) {
     Sym->Value = V.getValue();
   } else {
     Sym->Section = V.Sec;
-    if (Sym->Section->Flags & SHF_ALLOC)
-      Sym->Value = alignTo(V.Val, V.Alignment);
-    else
-      Sym->Value = V.getValue();
   }
 }
 
 static SymbolBody *findSymbol(StringRef S) {
   switch (Config->EKind) {
   case ELF32LEKind:
     return Symtab<ELF32LE>::X->find(S);
   case ELF32BEKind:

 
 // This function assigns offsets to input sections and an output section
 // for a single sections command (e.g. ".text { *(.text); }").
 void LinkerScript::assignOffsets(OutputSectionCommand *Cmd) {
   OutputSection *Sec = Cmd->Sec;
   if (!Sec)
     return;
 
-  if (Cmd->AddrExpr && (Sec->Flags & SHF_ALLOC))
+  if (!(Sec->Flags & SHF_ALLOC))
+    Dot = 0;
+  else if (Cmd->AddrExpr)
     setDot(Cmd->AddrExpr, Cmd->Location, false);
 
   if (Cmd->LMAExpr) {
     uint64_t D = Dot;
     LMAOffset = [=] { return Cmd->LMAExpr().getValue() - D; };
   }
 
   CurMemRegion = Cmd->MemRegion;
for (BaseCommand *Base : Opt.Commands) {
     assignOffsets(Cmd);
   }
 
   uint64_t MinVA = std::numeric_limits<uint64_t>::max();
   for (OutputSectionCommand *Cmd : OutputSectionCommands) {
     OutputSection *Sec = Cmd->Sec;
     if (Sec->Flags & SHF_ALLOC)
       MinVA = std::min<uint64_t>(MinVA, Sec->Addr);
-    else
-      Sec->Addr = 0;
   }
 
   allocateHeaders(Phdrs, OutputSectionCommands, MinVA);
 }
 
 // Creates program headers as instructed by PHDRS linker script command.
 std::vector<PhdrEntry> LinkerScript::createPhdrs(
     ArrayRef<OutputSectionCommand *> OutputSectionCommands) {

test/ELF/linkerscript/locationcountererr2.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
 # RUN: echo "SECTIONS {" > %t.script
-# RUN: echo ". = 0x20; . = 0x10; }" >> %t.script
+# RUN: echo ". = 0x20; . = 0x10; .text : {} }" >> %t.script
 # RUN: not ld.lld %t.o --script %t.script -o %t -shared 2>&1 | FileCheck %s
 # CHECK: {{.*}}.script:2: unable to move location counter backward
 
 # RUN: echo "SECTIONS { . = 0x20; . = ASSERT(0x1, "foo"); }" > %t2.script
 # RUN: ld.lld %t.o --script %t2.script -o %t -shared

test/ELF/linkerscript/symbols-non-alloc.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 
 # RUN: echo "SECTIONS { . = SIZEOF_HEADERS; \
 # RUN:  .text : { *(.text) }                \
 # RUN:  .nonalloc : { *(.nonalloc) }        \
 # RUN:  Sym = .;                            \
 # RUN:  }" > %t.script
 # RUN: ld.lld -o %t2 --script %t.script %t
 # RUN: llvm-objdump -section-headers -t %t2 | FileCheck %s
 
 # CHECK: Sections:
 # CHECK:  .nonalloc     00000008 0000000000000000
 
 # CHECK: SYMBOL TABLE:
-# CHECK:  00000000000000f0 .nonalloc 00000000 Sym
+# CHECK:  0000000000000008 .nonalloc 00000000 Sym
 
 .section .nonalloc,""
  .quad 0