[ELF] - Linkerscript: implemented LOADADDR()

[grimar]

Summary

Met that commind used in the wild, for example here:
https://searchcode.com/file/51551302/arch/x86_64/kernel/vmlinux.lds.S

LOADADDR(section)
  Return the absolute LMA of the named section. This is normally the same as
  ADDR, but it may be different if the AT attribute is used in the output section
  definition.

[evgeny777]

https://reviews.llvm.org/D24298

[evgeny777]

ELF/LinkerScript.cpp

732

Looks like this is not correct.
From https://sourceware.org/binutils/docs-2.20/ld/Output-Section-LMA.html

If neither AT nor AT> is specified for an allocatable section, the linker will set the LMA such that the difference between VMA and LMA for the section is the same as the preceding output section in the same region

[grimar]

In D24910#552103, @evgeny777 wrote:

https://reviews.llvm.org/D24298

Ah, I missed we have one on review :(

ELF/LinkerScript.h

 class LinkerScriptBase {
 protected:
   ~LinkerScriptBase() = default;
 
 public:
   virtual uint64_t getOutputSectionAddress(StringRef Name) = 0;
   virtual uint64_t getOutputSectionSize(StringRef Name) = 0;
   virtual uint64_t getOutputSectionAlign(StringRef Name) = 0;
+  virtual uint64_t getOutputSectionLoadAddress(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.
 struct ScriptConfiguration {
   // Used to assign addresses to sections.
public:
   Expr getLma(StringRef Name);
   bool shouldKeep(InputSectionBase<ELFT> *S);
   void assignOffsets(OutputSectionCommand *Cmd);
   void assignAddresses();
   bool hasPhdrsCommands();
   uint64_t getOutputSectionAddress(StringRef Name) override;
   uint64_t getOutputSectionSize(StringRef Name) override;
   uint64_t getOutputSectionAlign(StringRef Name) override;
+  uint64_t getOutputSectionLoadAddress(StringRef Name) override;
   uint64_t getHeaderSize() override;
   uint64_t getSymbolValue(StringRef S) override;
   bool isDefined(StringRef S) override;
 
   std::vector<OutputSectionBase<ELFT> *> *OutputSections;
 
   int getSectionIndex(StringRef Name);
 

ELF/LinkerScript.cpp

uint64_t LinkerScript<ELFT>::getOutputSectionAddress(StringRef Name) {
   for (OutputSectionBase<ELFT> *Sec : *OutputSections)
     if (Sec->getName() == Name)
       return Sec->getVA();
   error("undefined section " + Name);
   return 0;
 }
 
 template <class ELFT>
+uint64_t LinkerScript<ELFT>::getOutputSectionLoadAddress(StringRef Name) {
+  uint64_t VA = getOutputSectionAddress(Name);
+  if (Expr LmaExpr = getLma(Name))
+    return LmaExpr(VA);
+  return VA;
+}
+
+template <class ELFT>
 uint64_t LinkerScript<ELFT>::getOutputSectionSize(StringRef Name) {
   for (OutputSectionBase<ELFT> *Sec : *OutputSections)
     if (Sec->getName() == Name)
       return Sec->getSize();
   error("undefined section " + Name);
   return 0;
 }
 
Expr ScriptParser::readPrimary() {
   if (Tok == "DATA_SEGMENT_RELRO_END") {
     expect("(");
     readExpr();
     expect(",");
     readExpr();
     expect(")");
     return [](uint64_t Dot) { return alignTo(Dot, Target->PageSize); };
   }
+  if (Tok == "LOADADDR") {
+    expect("(");
+    StringRef Name = next();
+    expect(")");
+    return [=](uint64_t Dot) {
+      return ScriptBase->getOutputSectionLoadAddress(Name);
+    };
+  }
   if (Tok == "SIZEOF") {
     expect("(");
     StringRef Name = next();
     expect(")");
     return [=](uint64_t Dot) { return ScriptBase->getOutputSectionSize(Name); };
   }
   if (Tok == "ALIGNOF") {
     expect("(");

test/ELF/linkerscript/loadaddr.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+
+# RUN: echo "SECTIONS {                    \
+# RUN:  . = 0x10000;                       \
+# RUN:  .foo : AT(0x15000) { *(.foo*) }    \
+# RUN:  .bar LOADADDR(.foo) : { *(.bar*) } \
+# RUN: }" > %t.script
+# RUN: ld.lld -o %t1 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t1 | FileCheck %s
+# CHECK:      Sections:
+# CHECK-NEXT: Idx Name          Size      Address          Type
+# CHECK-NEXT:   0               00000000 0000000000000000
+# CHECK-NEXT:   1 .foo          00000008 0000000000010000 DATA
+# CHECK-NEXT:   2 .bar          00000008 0000000000015000 DATA
+
+# RUN: echo "SECTIONS {                    \
+# RUN:  . = 0x10000;                       \
+# RUN:  .foo : { *(.foo*) }    \
+# RUN:  .bar LOADADDR(.foo) + 0x100 : { *(.bar*) } \
+# RUN: }" > %t.script
+# RUN: ld.lld -o %t2 --script %t.script %t
+# RUN: llvm-objdump -section-headers %t2 | FileCheck %s --check-prefix=NO-AT
+# NO-AT:      Sections:
+# NO-AT-NEXT: Idx Name          Size      Address          Type
+# NO-AT-NEXT:   0               00000000 0000000000000000
+# NO-AT-NEXT:   1 .foo          00000008 0000000000010000 DATA
+# NO-AT-NEXT:   2 .bar          00000008 0000000000010100 DATA
+
+## Check that we error out if trying to get load address of
+## section that does not exist.
+# RUN: echo "SECTIONS { .bar LOADADDR(.zed) : { *(.bar*) } }" > %t.script
+# RUN: not ld.lld -o %t1 --script %t.script %t 2>&1 \
+# RUN:  | FileCheck -check-prefix=ERR %s
+# ERR: undefined section .zed
+
+.global _start
+_start:
+ nop
+
+.section .foo,"a"
+.quad 1
+
+.section .bar,"a"
+.quad 1