[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

795–796

Make this a member function.

798–799

This is better.

return 4096;  // return a dummy value

802

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

[grimar]

• Addressed review comments.

[ruiu]

ELF/ScriptParser.cpp

795–796

Rename getPageSize.

797

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

805

Rename readConstant.

[grimar]

• Addressed review comments.

[ruiu]

LGTM

ELF/ScriptParser.cpp

806

This doesn't capture anything so remove =

ELF/ScriptParser.cpp

while (!atEOF()) {
         break;
       Rhs = readExpr1(Rhs, precedence(Op2));
     }
 
     Lhs = combine(Op1, Lhs, Rhs);
   }
   return Lhs;
 }
 
-uint64_t static getConstant(StringRef S) {
-  if (S == "COMMONPAGESIZE")
+uint64_t static getConstant(StringRef S, StringRef Location) {
+  if (S == "COMMONPAGESIZE") {
+    if (Target)
       return Target->PageSize;
+    error(Location + ": unable to calculate: " + S);
+    return 0;
+  }
   if (S == "MAXPAGESIZE")
     return Config->MaxPageSize;
   error("unknown constant: " + S);
   return 0;
 }
 
 // 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 (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); };
+    return [=] { return getConstant(Name, Location); };
   }
   if (Tok == "DATA_SEGMENT_ALIGN") {
     expect("(");
     Expr E = readExpr();
     expect(",");
     readExpr();
     expect(")");
     return [=] {
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); };
+    return [=] {
+      if (!Target) {
+        error(Location + ": unable to calculate: " + Tok);
+        return (uint64_t)0;
+      }
+      return alignTo(Script->getDot(), Target->PageSize);
+    };
   }
   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 |\
+# RUN:   FileCheck %s --check-prefix=ERR1
+# ERR1: error: {{.*}}.script:1: unable to calculate: DATA_SEGMENT_RELRO_END
+
+# 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: COMMONPAGESIZE