[ELF2] Add ENTRY command to the linker script

[denis-protivensky]

Summary

Parse ENTRY command, set it as an entry point if -e is not specified.

[ruiu]

LGTM with nits.

ELF/LinkerScript.cpp

41

Sort.

53–56

Move ENTRY before GROUP to sort them.

151–159

Move this above readGroup.

test/elf2/linkerscript.s

27

Indent with two spaces.

[denis-protivensky]

Will fix style and sort members before commit.

ELF/LinkerScript.cpp

private:
   static std::vector<StringRef> tokenize(StringRef S);
   static StringRef skipSpace(StringRef S);
   StringRef next();
   bool atEOF() { return Tokens.size() == Pos; }
   void expect(StringRef Expect);
 
   void readAsNeeded();
   void readGroup();
+  void readEntry();
   void readOutput();
   void readOutputFormat();
 
   std::vector<StringRef> Tokens;
   size_t Pos = 0;
 };
 }
 
 void LinkerScript::run() {
   while (!atEOF()) {
     StringRef Tok = next();
     if (Tok == "GROUP") {
       readGroup();
+    } else if (Tok == "ENTRY") {
+      readEntry();
     } else if (Tok == "OUTPUT") {
       readOutput();
     } else if (Tok == "OUTPUT_FORMAT") {
       readOutputFormat();
     } else {
       error("unknown directive: " + Tok);
     }
   }
for (;;) {
     if (Tok == "AS_NEEDED") {
       readAsNeeded();
       continue;
     }
     Driver->addFile(Tok);
   }
 }
 
+void LinkerScript::readEntry() {
+  // -e <symbol> takes predecence over ENTRY(<symbol>).
+  expect("(");
+  StringRef Tok = next();
+  if (Config->Entry.empty())
+    Config->Entry = Tok;
+  expect(")");
+}
+
 void LinkerScript::readOutput() {
   // -o <file> takes predecence over OUTPUT(<file>).
   expect("(");
   StringRef Tok = next();
   if (Config->OutputFile.empty())
     Config->OutputFile = Tok;
   expect(")");
 }

test/elf2/linkerscript.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
 
 # RUN: echo "GROUP(" %t ")" > %t.script
 # RUN: lld -flavor gnu2 -o %t2 %t.script
 # RUN: llvm-readobj %t2 > /dev/null
 
 # RUN: echo "GROUP(" %t.script2 ")" > %t.script1
 # RUN: echo "GROUP(" %t ")" > %t.script2
 # RUN: lld -flavor gnu2 -o %t2 %t.script1
 # RUN: llvm-readobj %t2 > /dev/null
 
+# RUN: echo "ENTRY(_label)" > %t.script
+# RUN: lld -flavor gnu2 -o %t2 %t.script %t
+# RUN: llvm-readobj %t2 > /dev/null
+
+# RUN: echo "ENTRY(_wrong_label)" > %t.script
+# RUN: not lld -flavor gnu2 -o %t2 %t.script %t > %t.log 2>&1
+# RUN: FileCheck -check-prefix=ERR-ENTRY %s < %t.log
+
+# ERR-ENTRY: undefined symbol: _wrong_label
+
+# -e has precedence over linker script's ENTRY.
+# RUN: echo "ENTRY(_label)" > %t.script
+# RUN: lld -flavor gnu2 -e _start -o %t2 %t.script %t
+# RUN: llvm-readobj -file-headers -symbols %t2 | \
+# RUN: FileCheck -check-prefix=ENTRY-OVERLOAD %s
+
+# ENTRY-OVERLOAD: Entry: [[ENTRY:0x[0-9A-F]+]]
+# ENTRY-OVERLOAD: Name: _start
+# ENTRY-OVERLOAD-NEXT: Value: [[ENTRY]]
+
 # RUN: echo "OUTPUT_FORMAT(\"elf64-x86-64\") /*/*/ GROUP(" %t ")" > %t.script
 # RUN: lld -flavor gnu2 -o %t2 %t.script
 # RUN: llvm-readobj %t2 > /dev/null
 
 # RUN: echo "GROUP(AS_NEEDED(" %t "))" > %t.script
 # RUN: lld -flavor gnu2 -o %t2 %t.script
 # RUN: llvm-readobj %t2 > /dev/null
 
 # RUN: rm -f %t.out
 # RUN: echo "OUTPUT(" %t.out ")" > %t.script
 # RUN: lld -flavor gnu2 %t.script %t
 # RUN: llvm-readobj %t.out > /dev/null
 
 # RUN: echo "FOO(BAR)" > %t.script
 # RUN: not lld -flavor gnu2 -o foo %t.script > %t.log 2>&1
 # RUN: FileCheck -check-prefix=ERR1 %s < %t.log
 
 # ERR1: unknown directive: FOO
 
-.globl _start;
+.globl _start, _label;
 _start:
   mov $60, %rax
   mov $42, %rdi
+_label:
   syscall