[ELF] Handle output section alignment in linker scripts

[phosek]

Summary

LLD already parses ALIGN expression to specify alignment for output sections in linker scripts but it never applied the alignment to the output section.

[ruiu]

ELF/LinkerScript.cpp

372

I don't know if this is the right place to add this code. Have all output sections been created when the control reaches here? I think LinkerScript<ELFT>::assignOffsets is a better place to do this.

[phosek]

ELF/LinkerScript.cpp

372

I think they should, but assignOffsets would definitely work.

[ruiu]

LGTM

ELF/LinkerScript.cpp

if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base1.get())) {
         for (InputSectionBase<ELFT> *S : V)
           S->Alignment = Subalign;
       }
 
       // Add input sections to an output section.
       for (InputSectionBase<ELFT> *S : V)
         addSection(Factory, S, Cmd->Name);
     }
   }
 }
 
 // Add sections that didn't match any sections command.
 template <class ELFT>
 void LinkerScript<ELFT>::addOrphanSections(
     OutputSectionFactory<ELFT> &Factory) {
   for (InputSectionBase<ELFT> *S : Symtab<ELFT>::X->Sections)
     if (S->Live && !S->OutSec)

 template <class ELFT>
 void LinkerScript<ELFT>::assignOffsets(OutputSectionCommand *Cmd) {
   if (Cmd->LMAExpr)
     LMAOffset = Cmd->LMAExpr(Dot) - Dot;
   OutputSectionBase *Sec = findSection<ELFT>(Cmd->Name, *OutputSections);
   if (!Sec)
     return;
 
+  // Handle align (e.g. ".foo : ALIGN(16) { ... }").
+  if (Cmd->AlignExpr)
+    Sec->updateAlignment(Cmd->AlignExpr(0));
+
   // Try and find an appropriate memory region to assign offsets in.
   CurMemRegion = findMemoryRegion(Cmd, Sec);
   if (CurMemRegion)
     Dot = CurMemRegion->Offset;
   switchTo(Sec);
 
   // Find the last section output location. We will output orphan sections
   // there so that end symbols point to the correct location.

test/ELF/linkerscript/section-align.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS { \
+# RUN:   .aaa : ALIGN(4096) { *(.aaa) } \
+# RUN:   .bbb : ALIGN(4096 * 4) { *(.bbb) } \
+# RUN:   .ccc : ALIGN(4096 * 8) { *(.ccc) } \
+# RUN: }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-readobj -sections %t1 | FileCheck %s
+
+.global _start
+_start:
+ nop
+
+// CHECK:      Name: .aaa
+// CHECK-NEXT: Type: SHT_PROGBITS
+// CHECK-NEXT: Flags [
+// CHECK-NEXT:   SHF_ALLOC
+// CHECK-NEXT: ]
+// CHECK-NEXT: Address:
+// CHECK-NEXT: Offset:
+// CHECK-NEXT: Size: 8
+// CHECK-NEXT: Link: 0
+// CHECK-NEXT: Info: 0
+// CHECK-NEXT: AddressAlignment: 4096
+// CHECK-NEXT: EntrySize:
+
+.section .aaa, "a"
+.quad 0
+
+// CHECK:      Name: .bbb
+// CHECK-NEXT: Type: SHT_PROGBITS
+// CHECK-NEXT: Flags [
+// CHECK-NEXT:   SHF_ALLOC
+// CHECK-NEXT: ]
+// CHECK-NEXT: Address:
+// CHECK-NEXT: Offset:
+// CHECK-NEXT: Size: 8
+// CHECK-NEXT: Link: 0
+// CHECK-NEXT: Info: 0
+// CHECK-NEXT: AddressAlignment: 16384
+// CHECK-NEXT: EntrySize:
+
+.section .bbb, "a"
+.quad 0
+
+// CHECK:      Name: .ccc
+// CHECK-NEXT: Type: SHT_PROGBITS
+// CHECK-NEXT: Flags [
+// CHECK-NEXT:   SHF_ALLOC
+// CHECK-NEXT: ]
+// CHECK-NEXT: Address:
+// CHECK-NEXT: Offset:
+// CHECK-NEXT: Size: 8
+// CHECK-NEXT: Link: 0
+// CHECK-NEXT: Info: 0
+// CHECK-NEXT: AddressAlignment: 32768
+// CHECK-NEXT: EntrySize:
+
+.section .ccc, "a"
+.quad 0