[ELF] - Linkerscript: implemented FILL command as alias for =fillexpr

[grimar]

Summary

In compare with D24186 patch which provides implementation that is
fully equal to specification, this patch implements FILL just as alias
for =fillexpr.
This allows to make implementation much shorted and simpler.

[• rafael]

LGTM.

ELF/LinkerScript.cpp

private:
   void readOutputFormat();
   void readPhdrs();
   void readSearchDir();
   void readSections();
   void readVersion();
   void readVersionScriptCommand();
 
   SymbolAssignment *readAssignment(StringRef Name);
+  std::vector<uint8_t> readFill();
   OutputSectionCommand *readOutputSectionDescription(StringRef OutSec);
-  std::vector<uint8_t> readOutputSectionFiller();
+  std::vector<uint8_t> readOutputSectionFiller(StringRef Tok);
   std::vector<StringRef> readOutputSectionPhdrs();
   InputSectionDescription *readInputSectionDescription(StringRef Tok);
   Regex readFilePatterns();
   InputSectionDescription *readInputSectionRules(StringRef FilePattern);
   unsigned readPhdrType();
   SortKind readSortKind();
   SymbolAssignment *readProvideHidden(bool Provide, bool Hidden);
   SymbolAssignment *readProvideOrAssignment(StringRef Tok);
Expr ScriptParser::readAssert() {
   return [=](uint64_t Dot) {
     uint64_t V = E(Dot);
     if (!V)
       error(Msg);
     return V;
   };
 }
 
+std::vector<uint8_t> ScriptParser::readFill() {
+  expect("(");
+  std::vector<uint8_t> V = readOutputSectionFiller(next());
+  expect(")");
+  expect(";");
+  return V;
+}
+
 OutputSectionCommand *
 ScriptParser::readOutputSectionDescription(StringRef OutSec) {
   OutputSectionCommand *Cmd = new OutputSectionCommand(OutSec);
 
   // Read an address expression.
   // https://sourceware.org/binutils/docs/ld/Output-Section-Address.html#Output-Section-Address
   if (peek() != ":")
     Cmd->AddrExpr = readExpr();
ScriptParser::readOutputSectionDescription(StringRef OutSec) {
   if (skip("ONLY_IF_RW"))
     Cmd->Constraint = ConstraintKind::ReadWrite;
   expect("{");
 
   while (!Error && !skip("}")) {
     StringRef Tok = next();
     if (SymbolAssignment *Assignment = readProvideOrAssignment(Tok))
       Cmd->Commands.emplace_back(Assignment);
+    else if (Tok == "FILL")
+      Cmd->Filler = readFill();
     else if (Tok == "SORT")
       readSort();
     else if (peek() == "(")
       Cmd->Commands.emplace_back(readInputSectionDescription(Tok));
     else
       setError("unknown command " + Tok);
   }
   Cmd->Phdrs = readOutputSectionPhdrs();
-  Cmd->Filler = readOutputSectionFiller();
+  if (peek().startswith("="))
+    Cmd->Filler = readOutputSectionFiller(next().drop_front());
   return Cmd;
 }
 
 // Read "=<number>" where <number> is an octal/decimal/hexadecimal number.
 // https://sourceware.org/binutils/docs/ld/Output-Section-Fill.html
 //
 // ld.gold is not fully compatible with ld.bfd. ld.bfd handles
 // hexstrings as blobs of arbitrary sizes, while ld.gold handles them
 // as 32-bit big-endian values. We will do the same as ld.gold does
 // because it's simpler than what ld.bfd does.
-std::vector<uint8_t> ScriptParser::readOutputSectionFiller() {
-  if (!peek().startswith("="))
-    return {};
-
-  StringRef Tok = next();
+std::vector<uint8_t> ScriptParser::readOutputSectionFiller(StringRef Tok) {
   uint32_t V;
-  if (Tok.substr(1).getAsInteger(0, V)) {
+  if (Tok.getAsInteger(0, V)) {
     setError("invalid filler expression: " + Tok);
     return {};
   }
   return {uint8_t(V >> 24), uint8_t(V >> 16), uint8_t(V >> 8), uint8_t(V)};
 }
 
 SymbolAssignment *ScriptParser::readProvideHidden(bool Provide, bool Hidden) {
   expect("(");

test/ELF/linkerscript/linkerscript-fill.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: echo "SECTIONS {     \
+# RUN:  .out : {            \
+# RUN:   FILL(0x11111111);  \
+# RUN:   *(.aaa)            \
+# RUN:   . += 4;            \
+# RUN:   *(.bbb)            \
+# RUN:   . += 4;            \
+# RUN:   FILL(0x22222222);  \
+# RUN:   . += 4;            \
+# RUN:  }                   \
+# RUN: }; " > %t.script
+# RUN: ld.lld -o %t --script %t.script %t.o
+# RUN: llvm-objdump -s %t | FileCheck %s
+
+# CHECK:      Contents of section .out:
+# CHECK-NEXT: 0120 aa222222 22bb2222 22222222 2222
+
+.text
+.globl _start
+_start:
+
+.section .aaa, "a"
+.align 1
+.byte 0xAA
+
+.section .bbb, "a"
+.align 1
+.byte 0xBB

test/ELF/linkerscript/sections-padding.s

 # RUN: ld.lld -o %t.out --script %t.script %t
 # RUN: llvm-objdump -s %t.out | FileCheck -check-prefix=DEC %s
 # DEC: 0120  66000309 00000309 00000309 00000309
 
 ## Invalid hex value:
 # RUN: echo "SECTIONS { .mysec : { *(.mysec*) } =0x99XX }" > %t.script
 # RUN: not ld.lld -o %t.out --script %t.script %t 2>&1 \
 # RUN:   | FileCheck --check-prefix=ERR2 %s
-# ERR2: invalid filler expression: =0x99XX
+# ERR2: invalid filler expression: 0x99XX
 
 .section        .mysec.1,"a"
 .align  16
 .byte   0x66
 
 .section        .mysec.2,"a"
 .align  16
 .byte   0x66
 
 .globl _start
 _start:
  nop