Support ABSOLUTE on the right hand side in linker scripts

This also requires postponing the assignment the assignment of
symbols defined in input linker scripts since those can refer to
output sections and in case we don't have a SECTIONS command, we
need to wait until all output sections have been created and
assigned addresses.

Differential Revision: https://reviews.llvm.org/D30851

llvm-svn: 297802

lld/ELF/LinkerScript.cpp

@@ -153,11 +153,6 @@ void LinkerScript<ELFT>::addSymbol(SymbolAssignment *Cmd) {
     return;
 
   Cmd->Sym = addRegular<ELFT>(Cmd);
-
-  // If there are sections, then let the value be assigned later in
-  // `assignAddresses`.
-  if (!ScriptConfig->HasSections)
-    assignSymbol(Cmd);
 }
 
 bool SymbolAssignment::classof(const BaseCommand *C) {
@@ -344,15 +339,6 @@ void LinkerScript<ELFT>::processCommands(OutputSectionFactory &Factory) {
       continue;
     }
 
-    if (auto *Cmd = dyn_cast<AssertCommand>(Base1.get())) {
-      // If we don't have SECTIONS then output sections have already been
-      // created by Writer<ELFT>. The LinkerScript<ELFT>::assignAddresses
-      // will not be called, so ASSERT should be evaluated now.
-      if (!Opt.HasSections)
-        Cmd->Expression();
-      continue;
-    }
-
     if (auto *Cmd = dyn_cast<OutputSectionCommand>(Base1.get())) {
       std::vector<InputSectionBase *> V = createInputSectionList(*Cmd);
 
@@ -779,6 +765,15 @@ void LinkerScriptBase::placeOrphanSections() {
   }
 }
 
+void LinkerScriptBase::processNonSectionCommands() {
+  for (const std::unique_ptr<BaseCommand> &Base : Opt.Commands) {
+    if (auto *Cmd = dyn_cast<SymbolAssignment>(Base.get()))
+      assignSymbol(Cmd);
+    else if (auto *Cmd = dyn_cast<AssertCommand>(Base.get()))
+      Cmd->Expression();
+  }
+}
+
 void LinkerScriptBase::assignAddresses(std::vector<PhdrEntry> &Phdrs) {
   // Assign addresses as instructed by linker script SECTIONS sub-commands.
   Dot = 0;
@@ -1556,14 +1551,8 @@ SymbolAssignment *ScriptParser::readProvideOrAssignment(StringRef Tok) {
 
 SymbolAssignment *ScriptParser::readAssignment(StringRef Name) {
   StringRef Op = next();
-  Expr E;
   assert(Op == "=" || Op == "+=");
-  if (consume("ABSOLUTE")) {
-    E = readExpr();
-    E.IsAbsolute = [] { return true; };
-  } else {
-    E = readExpr();
-  }
+  Expr E = readExpr();
   if (Op == "+=") {
     std::string Loc = getCurrentLocation();
     E = [=] { return ScriptBase->getSymbolValue(Loc, Name) + E(); };
@@ -1739,6 +1728,11 @@ Expr ScriptParser::readPrimary() {
 
   // Built-in functions are parsed here.
   // https://sourceware.org/binutils/docs/ld/Builtin-Functions.html.
+  if (Tok == "ABSOLUTE") {
+    Expr E = readParenExpr();
+    E.IsAbsolute = [] { return true; };
+    return E;
+  }
   if (Tok == "ADDR") {
     StringRef Name = readParenLiteral();
     return {[=] { return ScriptBase->getOutputSection(Location, Name)->Addr; },

lld/ELF/LinkerScript.h

@@ -287,6 +287,7 @@ public:
   bool shouldKeep(InputSectionBase *S);
   void assignOffsets(OutputSectionCommand *Cmd);
   void placeOrphanSections();
+  void processNonSectionCommands();
   void assignAddresses(std::vector<PhdrEntry> &Phdrs);
   int getSectionIndex(StringRef Name);
 };

lld/ELF/Writer.cpp

@@ -270,6 +270,7 @@ template <class ELFT> void Writer<ELFT>::run() {
     } else {
       fixSectionAlignments();
       assignAddresses();
+      Script<ELFT>::X->processNonSectionCommands();
     }
 
     // Remove empty PT_LOAD to avoid causing the dynamic linker to try to mmap a

lld/test/ELF/linkerscript/absolute.s

@@ -4,6 +4,11 @@
 # RUN: ld.lld -o %t --script %t.script %t.o
 # RUN: llvm-readobj --symbols %t | FileCheck %s
 
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: echo "PROVIDE(foo = 1 + ABSOLUTE(ADDR(.text)));" > %t.script
+# RUN: ld.lld -o %t --script %t.script %t.o
+# RUN: llvm-readobj --symbols %t | FileCheck --check-prefix=CHECK-RHS %s
+
 # CHECK:        Name: foo
 # CHECK-NEXT:   Value:
 # CHECK-NEXT:   Size:
@@ -13,6 +18,18 @@
 # CHECK-NEXT:   Section: Absolute
 # CHECK-NEXT: }
 
+# CHECK-RHS:        Name: foo
+# CHECK-RHS-NEXT:   Value: 0x201001
+# CHECK-RHS-NEXT:   Size:
+# CHECK-RHS-NEXT:   Binding:
+# CHECK-RHS-NEXT:   Type:
+# CHECK-RHS-NEXT:   Other:
+# CHECK-RHS-NEXT:   Section: Absolute
+# CHECK-RHS-NEXT: }
+
 .text
 .globl _start
 _start:
+ nop
+
+.global foo