Make filler expression compatible with gold.

[ruiu]

Summary

Previously, a decimal filler expression is interpreted as a byte value.
Gold on the other hand use it as a 32-bit big-endian value.
This patch fixes the compatibility issue.

[davide]

lg

[davide]

Assuming the output is the same of gold.

lld/trunk/ELF/LinkerScript.cpp

void ScriptParser::readOutputSectionDescription(StringRef OutSec) {
   Cmd->Filler = readOutputSectionFiller();
 }
 
 std::vector<uint8_t> ScriptParser::readOutputSectionFiller() {
   StringRef Tok = peek();
   if (!Tok.startswith("="))
     return {};
   next();
+
+  // Read a hexstring of arbitrary length.
   if (Tok.startswith("=0x"))
     return parseHex(Tok.substr(3));
 
-  // This must be a decimal.
-  unsigned int Value;
-  if (Tok.substr(1).getAsInteger(10, Value)) {
-    setError("filler should be a decimal/hexadecimal value");
+  // Read a decimal or octal value as a big-endian 32 bit value.
+  // Why do this? I don't know, but that's what gold does.
+  uint32_t V;
+  if (Tok.substr(1).getAsInteger(0, V)) {
+    setError("invalid filler expression: " + Tok);
     return {};
   }
-  if (Value > 255)
-    setError("only single bytes decimal are supported for the filler now");
-  return {static_cast<unsigned char>(Value)};
+  return { uint8_t(V >> 24), uint8_t(V >> 16), uint8_t(V >> 8), uint8_t(V) };
 }
 
 void ScriptParser::readProvide(bool Hidden) {
   expect("(");
   SymbolAssignment *Cmd = readAssignment(next());
   Cmd->Provide = true;
   Cmd->Hidden = Hidden;
   expect(")");

lld/trunk/test/ELF/linkerscript/linkerscript-sections-padding.s

 
 ## Default padding value is 0x00:
 # RUN: echo "SECTIONS { .mysec : { *(.mysec*) } }" > %t.script
 # RUN: ld.lld -o %t.out --script %t.script %t
 # RUN: hexdump -C %t.out | FileCheck -check-prefix=NO %s
 # NO: 00000120  66 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 
 ## Decimal value.
-# RUN: echo "SECTIONS { .mysec : { *(.mysec*) } =99 }" > %t.script
+# RUN: echo "SECTIONS { .mysec : { *(.mysec*) } =777 }" > %t.script
 # RUN: ld.lld -o %t.out --script %t.script %t
 # RUN: hexdump -C %t.out | FileCheck -check-prefix=DEC %s
-# DEC: 00000120  66 63 63 63 63 63 63 63  63 63 63 63 63 63 63 63
+# DEC: 00000120  66 00 03 09 00 00 03 09 00 00 03 09 00 00 03 09
 
 ## 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: not a hexadecimal value: XX
 
 .section        .mysec.1,"a"