[ELF] Linkerscript: symbol assignments with indentifiers on the right side of expression.

In symbol assignments symbol may appear on the right-hand side of the expression:
(https://svnweb.freebsd.org/base/head/sys/conf/ldscript.amd64?revision=284870&view=markup#l8)

kernphys = CONSTANT (MAXPAGESIZE);
 . = kernbase + kernphys + SIZEOF_HEADERS;

Patch implements that.

Differential revision: https://reviews.llvm.org/D22759

llvm-svn: 276784

2 files changed, 61 insertions, 3 deletions

diff --git a/lld/ELF/LinkerScript.cpp b/lld/ELF/LinkerScript.cpp
index 3889f104ecf..1079a2fa99b 100644
--- a/lld/ELF/LinkerScript.cpp
+++ b/lld/ELF/LinkerScript.cpp
@@ -756,6 +756,29 @@ SymbolAssignment *ScriptParser::readAssignment(StringRef Name) {
 // script expression.
 Expr ScriptParser::readExpr() { return readExpr1(readPrimary(), 0); }
 
+static uint64_t getSymbolValue(StringRef S) {
+  switch (Config->EKind) {
+  case ELF32LEKind:
+    if (SymbolBody *B = Symtab<ELF32LE>::X->find(S))
+      return B->getVA<ELF32LE>();
+    break;
+  case ELF32BEKind:
+    if (SymbolBody *B = Symtab<ELF32BE>::X->find(S))
+      return B->getVA<ELF32BE>();
+    break;
+  case ELF64LEKind:
+    if (SymbolBody *B = Symtab<ELF64LE>::X->find(S))
+      return B->getVA<ELF64LE>();
+    break;
+  case ELF64BEKind:
+    if (SymbolBody *B = Symtab<ELF64BE>::X->find(S))
+      return B->getVA<ELF64BE>();
+    break;
+  }
+  error("symbol not found: " + S);
+  return 0;
+}
+
 // This is a part of the operator-precedence parser. This function
 // assumes that the remaining token stream starts with an operator.
 Expr ScriptParser::readExpr1(Expr Lhs, int MinPrec) {
@@ -844,10 +867,13 @@ Expr ScriptParser::readPrimary() {
     return [](uint64_t Dot) { return alignTo(Dot, Target->PageSize); };
   }
 
-  // Parse a number literal
+  // Parse a symbol name or a number literal.
   uint64_t V = 0;
-  if (Tok.getAsInteger(0, V))
-    setError("malformed number: " + Tok);
+  if (Tok.getAsInteger(0, V)) {
+    if (!isValidCIdentifier(Tok))
+      setError("malformed number: " + Tok);
+    return [=](uint64_t Dot) { return getSymbolValue(Tok); };
+  }
   return [=](uint64_t Dot) { return V; };
 }
 
diff --git a/lld/test/ELF/linkerscript/linkerscript-symbol-assignexpr.s b/lld/test/ELF/linkerscript/linkerscript-symbol-assignexpr.s
new file mode 100644
index 00000000000..353800b6de6
--- /dev/null
+++ b/lld/test/ELF/linkerscript/linkerscript-symbol-assignexpr.s
@@ -0,0 +1,32 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS { \
+# RUN:         symbol = CONSTANT(MAXPAGESIZE); \
+# RUN:         symbol2 = symbol + 0x1234; \
+# RUN:         symbol3 = symbol2; \
+# RUN:       }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -t %t1 | FileCheck %s
+
+# CHECK:      SYMBOL TABLE:
+# CHECK-NEXT: 0000000000000000 *UND* 00000000
+# CHECK-NEXT: 0000000000000120 .text 00000000 _start
+# CHECK-NEXT: 0000000000000121 .text 00000000 foo
+# CHECK-NEXT: 0000000000001000 *ABS* 00000000 symbol
+# CHECK-NEXT: 0000000000002234 *ABS* 00000000 symbol2
+# CHECK-NEXT: 0000000000002234 *ABS* 00000000 symbol3
+
+# RUN: echo "SECTIONS { \
+# RUN:         symbol2 = symbol; \
+# RUN:       }" > %t2.script
+# RUN: not ld.lld -o %t2 --script %t2.script %t 2>&1 \
+# RUN:  | FileCheck -check-prefix=ERR %s
+# ERR: symbol not found: symbol
+
+.global _start
+_start:
+ nop
+
+.global foo
+foo: