[PATCH] D24858: [ELF] - Linkerscript: implement DEFINED() command.

[George Rimar via llvm-commits]

grimar created this revision.
grimar added reviewers: ruiu, rafael.
grimar added subscribers: llvm-commits, grimar, davide, evgeny777.

DEFINED(symbol)
Return 1 if symbol is in the linker global symbol table and is defined before
the statement using DEFINED in the script, otherwise return 0.

Can be used to define default values for symbols. Found it in the wild here:
https://searchcode.com/file/103745382/board/bf561-ezkit/u-boot.lds.S

Patch implements it.

https://reviews.llvm.org/D24858

Files:
  ELF/LinkerScript.cpp
  ELF/LinkerScript.h
  test/ELF/linkerscript/define.s

Index: test/ELF/linkerscript/define.s
===================================================================
--- test/ELF/linkerscript/define.s
+++ test/ELF/linkerscript/define.s
@@ -0,0 +1,25 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS                                \
+# RUN: {                                             \
+# RUN:  . = DEFINED(defined) ? 0x11000 : .;          \
+# RUN:  .foo : { *(.foo*) }                          \
+# RUN:  . = DEFINED(notdefined) ? 0x12000 : 0x13000; \
+# RUN:  .bar : { *(.bar*) }                          \
+# RUN: }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t1 | FileCheck %s
+
+# CHECK: 1 .foo  00000008 0000000000011000 DATA
+# CHECK: 2 .bar  00000008 0000000000013000 DATA
+# CHECK: 3 .text 00000000 0000000000013008 TEXT DATA
+
+.global defined
+defined = 0
+
+.section .foo,"a"
+.quad 1
+
+.section .bar,"a"
+.quad 1
Index: ELF/LinkerScript.h
===================================================================
--- ELF/LinkerScript.h
+++ ELF/LinkerScript.h
@@ -157,6 +157,7 @@
   virtual uint64_t getOutputSectionAlign(StringRef Name) = 0;
   virtual uint64_t getHeaderSize() = 0;
   virtual uint64_t getSymbolValue(StringRef S) = 0;
+  virtual bool isDefined(StringRef S) = 0;
 };
 
 // ScriptConfiguration holds linker script parse results.
@@ -203,6 +204,7 @@
   uint64_t getOutputSectionAlign(StringRef Name) override;
   uint64_t getHeaderSize() override;
   uint64_t getSymbolValue(StringRef S) override;
+  bool isDefined(StringRef S) override;
 
   std::vector<OutputSectionBase<ELFT> *> *OutputSections;
 
Index: ELF/LinkerScript.cpp
===================================================================
--- ELF/LinkerScript.cpp
+++ ELF/LinkerScript.cpp
@@ -756,6 +756,10 @@
   return 0;
 }
 
+template <class ELFT> bool LinkerScript<ELFT>::isDefined(StringRef S) {
+  return Symtab<ELFT>::X->find(S) != nullptr;
+}
+
 // Returns indices of ELF headers containing specific section, identified
 // by Name. Each index is a zero based number of ELF header listed within
 // PHDRS {} script block.
@@ -1484,6 +1488,14 @@
     expect(")");
     return [=](uint64_t Dot) { return getConstant(Tok); };
   }
+  if (Tok == "DEFINED") {
+    expect("(");
+    StringRef Tok = next();
+    expect(")");
+    return [=](uint64_t Dot) {
+      return ScriptBase->isDefined(Tok) ? 1 : 0;
+    };
+  }
   if (Tok == "SEGMENT_START") {
     expect("(");
     next();


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