[ELF] - Do not segfault if linkerscript tries to access Target too early.

[grimar]

Summary

Following possible scripts triggered accessing to Target when it was not yet
initialized (was nullptr).

MEMORY { name : ORIGIN = DATA_SEGMENT_RELRO_END; }

MEMORY { name : ORIGIN = CONSTANT(COMMONPAGESIZE); }

Patch errors out instead.

[ruiu]

Please define a helper function getPageSize() to avoid repeating the same error checking twice.

[grimar]

• Addressed review comment.

[ruiu]

ELF/ScriptParser.cpp

810

Make this a member function.

813–814

This is better.

return 4096;  // return a dummy value

817

Make this a member function of LinkerScript so that you don't need to pass Location.

[grimar]

• Addressed review comments.

[ruiu]

ELF/ScriptParser.cpp

798–809

Rename getPageSize.

800

return [=] -> uint64_t { to remove casts.

808

Rename readConstant.

[grimar]

• Addressed review comments.

[ruiu]

LGTM

ELF/ScriptParser.cpp

813

This doesn't capture anything so remove =

ELF/ScriptParser.cpp

private:
   InputSectionDescription *readInputSectionRules(StringRef FilePattern);
   unsigned readPhdrType();
   SortSectionPolicy readSortKind();
   SymbolAssignment *readProvideHidden(bool Provide, bool Hidden);
   SymbolAssignment *readProvideOrAssignment(StringRef Tok);
   void readSort();
   AssertCommand *readAssert();
   Expr readAssertExpr();
+  Expr readConstant();
+  Expr getPageSize();
 
   uint64_t readMemoryAssignment(StringRef, StringRef, StringRef);
   std::pair<uint32_t, uint32_t> readMemoryAttributes();
 
   Expr readExpr();
   Expr readExpr1(Expr Lhs, int MinPrec);
   StringRef readParenLiteral();
   Expr readPrimary();
while (!atEOF()) {
       Rhs = readExpr1(Rhs, precedence(Op2));
     }
 
     Lhs = combine(Op1, Lhs, Rhs);
   }
   return Lhs;
 }
 
-uint64_t static getConstant(StringRef S) {
-  if (S == "COMMONPAGESIZE")
+Expr ScriptParser::getPageSize() {
+  std::string Location = getCurrentLocation();
+  return [=]() -> uint64_t {
+    if (Target)
       return Target->PageSize;
+    error(Location + ": unable to calculate page size");
+    return 4096; // Return a dummy value.
+  };
+}
+
+Expr ScriptParser::readConstant() {
+  StringRef S = readParenLiteral();
+  if (S == "COMMONPAGESIZE")
+    return getPageSize();
   if (S == "MAXPAGESIZE")
-    return Config->MaxPageSize;
-  error("unknown constant: " + S);
-  return 0;
+    return [=] { return Config->MaxPageSize; };
+  setError("unknown constant: " + S);
+  return {};
 }
 
 // Parses Tok as an integer. It recognizes hexadecimal (prefixed with
 // "0x" or suffixed with "H") and decimal numbers. Decimal numbers may
 // have "K" (Ki) or "M" (Mi) suffixes.
 static Optional<uint64_t> parseInt(StringRef Tok) {
   // Negative number
   if (Tok.startswith("-")) {
     if (Optional<uint64_t> Val = parseInt(Tok.substr(1)))
       return -*Val;
Expr ScriptParser::readPrimary() {
   }
   if (Tok == "ALIGNOF") {
     StringRef Name = readParenLiteral();
     OutputSection *Cmd = Script->getOrCreateOutputSection(Name);
     return [=] { return checkSection(Cmd, Location)->Alignment; };
   }
   if (Tok == "ASSERT")
     return readAssertExpr();
-  if (Tok == "CONSTANT") {
-    StringRef Name = readParenLiteral();
-    return [=] { return getConstant(Name); };
-  }
+  if (Tok == "CONSTANT")
+    return readConstant();
   if (Tok == "DATA_SEGMENT_ALIGN") {
     expect("(");
     Expr E = readExpr();
     expect(",");
     readExpr();
     expect(")");
     return [=] {
       return alignTo(Script->getDot(), std::max((uint64_t)1, E().getValue()));
if (Tok == "DATA_SEGMENT_RELRO_END") {
     // GNU linkers implements more complicated logic to handle
     // DATA_SEGMENT_RELRO_END. We instead ignore the arguments and
     // just align to the next page boundary for simplicity.
     expect("(");
     readExpr();
     expect(",");
     readExpr();
     expect(")");
-    return [] { return alignTo(Script->getDot(), Target->PageSize); };
+    Expr E = getPageSize();
+    return [=] { return alignTo(Script->getDot(), E().getValue()); };
   }
   if (Tok == "DEFINED") {
     StringRef Name = readParenLiteral();
     return [=] { return Script->isDefined(Name) ? 1 : 0; };
   }
   if (Tok == "LENGTH") {
     StringRef Name = readParenLiteral();
     if (Script->Opt.MemoryRegions.count(Name) == 0)

test/ELF/linkerscript/memory-err.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo "MEMORY { name : ORIGIN = DATA_SEGMENT_RELRO_END; }" > %t.script
+# RUN: not ld.lld -shared -o %t2 --script %t.script %t 2>&1 | FileCheck %s
+# CHECK: error: {{.*}}.script:1: unable to calculate page size
+
+# RUN: echo "MEMORY { name : ORIGIN = CONSTANT(COMMONPAGESIZE); }" > %t.script
+# RUN: not ld.lld -shared -o %t2 --script %t.script %t 2>&1 |\
+# RUN:   FileCheck %s --check-prefix=ERR2
+# ERR2: error: {{.*}}.script:1: unable to calculate page size