Implement STARTUP linker script command.

[ruiu]

Summary

Implement STARTUP linker script command.

[ruiu]

• removed an unrelated change.

[davide]

GNU gold doesn't seem to implement this one, maybe the same effect can be obtained without a linkerscript? What are you planning to use this for?

[davide@cupiditate ~]$ cat script
STARTUP(mario)
[davide@cupiditate ~]$ ld.gold --script=script
ld.gold: error: script:1:1: syntax error, unexpected STARTUP, expecting $end
ld.gold: fatal error: unable to parse script file script
[davide@cupiditate ~]$ ld --script=script
ld: no input files

[davide]

ELF/Driver.cpp

695

Nit: lld not LLD.

[ruiu]

Someone tweeted me that LLD doesn't have STARTUP, so I took it, and after that I realized that gold doesn't support that (funny that gold only recognizes token "STARTUP", so apparently someone tried to support it but didn't actually do anything more than that.)

I won't push it until at least a bug is filed.

[ruiu]

LLVM and LLDB but lld? It feels odd that a proper noun is all lowercase letters.

[davide]

In D27070#604903, @ruiu wrote:

Someone tweeted me that LLD doesn't have STARTUP, so I took it, and after that I realized that gold doesn't support that (funny that gold only recognizes token "STARTUP", so apparently someone tried to support it but didn't actually do anything more than that.)

I won't push it until at least a bug is filed.

I'm not necessarily against this feature, but would like to understand the use-case more. Can you ask them to open a bug on llvm.org for those of us not using twitter?

[davide]

In D27070#604904, @ruiu wrote:

LLVM and LLDB but lld? It feels odd that a proper noun is all lowercase letters.

Apparently Michael chose the name, and it's the one we have in http://lld.llvm.org/
While here, it also feels very weird having lld not respecting acronyms, FWIW (e.g. Lto instead of LTO as it's spelled anywhere else in LLVM). I would like to make this change if you have no objections.

[ruiu]

Are you suggesting renaming lld to LLD? I'm not even sure if LLD is an acronym (what is it short for -- maybe LLVM's LD?)

If lld is still an official name, I'd vote for renaming it to LLD. lld is a command name, but as a proper noun, it should be spelled in upper case unelss there's strong reason to not do so.

[davide]

In D27070#604914, @ruiu wrote:

Are you suggesting renaming lld to LLD? I'm not even sure if LLD is an acronym (what is it short for -- maybe LLVM's LD?)

If lld is still an official name, I'd vote for renaming it to LLD. lld is a command name, but as a proper noun, it should be spelled in upper case unelss there's strong reason to not do so.

No, I don't personally want to rename lld to LLD (but I won't object if you want to do so).
I'm pointing that, in the source code, we should rename Lto to LTO (et similia).

[ruiu]

Out of curiosity, why do you prefer lld over LLD?

[davide]

In D27070#604925, @ruiu wrote:

Out of curiosity, why do you prefer lld over LLD?

I'm not necessarily in favor of it, but this seems the original name we have. What about the proposed rename?

[ruiu]

LLD's (or lld's) coding style should be the same as LLVM's.

[grimar]

ELF/LinkerScript.cpp

1249

May be better to inline this ?

test/ELF/linkerscript/startup.s

4

This creates "startup.s.tmp.dir" folder for me inside tools\lld\test\ELF\linkerscript\Output.
And looks that is the only folder inside at this moment.
So out tests previously did not do that and that is inconsistency.

Do you plan to do that for all tests ?

13

llvm-objdump -s -section=.text ?

16

I would suggest not to check the address here. Latest changes like max page size shows
that we have lot of testcase failing for reasons they should not.

29

STARTUP file 'nosuchfile' not found ?

[grimar]

test/ELF/linkerscript/startup.s

4

I think I had to clarify why I noticed that. Usually I use msvs output tab to extract command line with arguments of failing test.

When test uses %t (like all out test do), line is something like:

23> $ "C:/access_softek/c_make_build_dir/Debug/bin\ld.lld.EXE" "--full-shutdown" "C:\xxx\tools\lld\test\ELF\Output\eh-frame-merge.s.tmp.o" "C:\xxx\tools\lld\test\ELF\Output\eh-frame-merge.s.tmp.o" "-o" "C:\xxx\tools\lld\test\ELF\Output\eh-frame-merge.s.tmp" "-shared"

So I can just copy it to MSVS property page to "command arguments" and use it for debugger.

This test is different and does not use %t and creates local files in separate folder.
Line for it is:

23> C:/xxx/Debug/bin\ld.lld.EXE --full-shutdown -o exe -script=script foo.o bar.o

So I also need to set "working directory" property.
What is not a huge problem but a bit less convinent. Especially when one test do that and other - not.

ELF/Config.h

struct Configuration {
   llvm::StringRef Entry;
   llvm::StringRef Emulation;
   llvm::StringRef Fini;
   llvm::StringRef Init;
   llvm::StringRef LtoAAPipeline;
   llvm::StringRef LtoNewPmPasses;
   llvm::StringRef OutputFile;
   llvm::StringRef SoName;
+  llvm::StringRef Startup;
   llvm::StringRef Sysroot;
   std::string RPath;
   std::vector<VersionDefinition> VersionDefinitions;
   std::vector<llvm::StringRef> AuxiliaryList;
   std::vector<llvm::StringRef> DynamicList;
   std::vector<llvm::StringRef> SearchPaths;
   std::vector<llvm::StringRef> Undefined;
   std::vector<SymbolVersion> VersionScriptGlobals;

ELF/Driver.h

public:
   std::unique_ptr<CpioFile> Cpio; // for reproduce
 
 private:
   std::vector<MemoryBufferRef> getArchiveMembers(MemoryBufferRef MB);
   llvm::Optional<MemoryBufferRef> readFile(StringRef Path);
   void readConfigs(llvm::opt::InputArgList &Args);
   void createFiles(llvm::opt::InputArgList &Args);
   void inferMachineType();
+  void reorderFiles();
   template <class ELFT> void link(llvm::opt::InputArgList &Args);
 
   // True if we are in --whole-archive and --no-whole-archive.
   bool InWholeArchive = false;
 
   // True if we are in --start-lib and --end-lib.
   bool InLib = false;
 

ELF/Driver.cpp

for (InputFile *F : Files) {
     Config->EMachine = F->EMachine;
     Config->OSABI = F->OSABI;
     Config->MipsN32Abi = Config->EMachine == EM_MIPS && isMipsN32Abi(F);
     return;
   }
   error("target emulation unknown: -m or at least one .o file required");
 }
 
+// This is for linker script STARTUP command. If STARTUP(foo.o) is
+// specified, LLD reorders input files so that foo.o becomes the first
+// object file to be linked, assuming that the file's .text section
+// will become the executable's entry address.
+void LinkerDriver::reorderFiles() {
+  if (Config->Startup.empty())
+    return;
+  for (auto I = Files.begin(), E = Files.end(); I != E; ++I) {
+    InputFile *F = *I;
+    if (F->getName() != Config->Startup)
+      continue;
+    Files.erase(I);
+    Files.insert(Files.begin(), F);
+    return;
+  }
+  warn(Config->Startup + ": STARTUP file not found");
+}
+
 // Parses -image-base option.
 static uint64_t getImageBase(opt::InputArgList &Args) {
   // Use default if no -image-base option is given.
   // Because we are using "Target" here, this function
   // has to be called after the variable is initialized.
   auto *Arg = Args.getLastArg(OPT_image_base);
   if (!Arg)
     return Config->Pic ? 0 : Target->DefaultImageBase;
template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
 
   // Initialize Config->MaxPageSize. The default value is defined by
   // the target, but it can be overriden using the option.
   Config->MaxPageSize =
       getZOptionValue(Args, "max-page-size", Target->MaxPageSize);
   if (!isPowerOf2_64(Config->MaxPageSize))
     error("max-page-size: value isn't a power of 2");
 
+  // Process linker script STARTUP command.
+  reorderFiles();
+
   // Add all files to the symbol table. After this, the symbol table
   // contains all known names except a few linker-synthesized symbols.
   for (InputFile *F : Files)
     Symtab.addFile(F);
 
   // Add the start symbol.
   // It initializes either Config->Entry or Config->EntryAddr.
   // Note that AMDGPU binaries have no entries.

ELF/LinkerScript.cpp

private:
   void readGroup();
   void readInclude();
   void readOutput();
   void readOutputArch();
   void readOutputFormat();
   void readPhdrs();
   void readSearchDir();
   void readSections();
+  void readStartup();
   void readVersion();
   void readVersionScriptCommand();
 
   SymbolAssignment *readAssignment(StringRef Name);
   BytesDataCommand *readBytesDataCommand(StringRef Tok);
   uint32_t readFill();
   OutputSectionCommand *readOutputSectionDescription(StringRef OutSec);
   uint32_t readOutputSectionFiller(StringRef Tok);
while (!atEOF()) {
     } else if (Tok == "OUTPUT_FORMAT") {
       readOutputFormat();
     } else if (Tok == "PHDRS") {
       readPhdrs();
     } else if (Tok == "SEARCH_DIR") {
       readSearchDir();
     } else if (Tok == "SECTIONS") {
       readSections();
+    } else if (Tok == "STARTUP") {
+      readStartup();
     } else if (Tok == "VERSION") {
       readVersion();
     } else if (SymbolAssignment *Cmd = readProvideOrAssignment(Tok)) {
       Opt.Commands.emplace_back(Cmd);
     } else {
       setError("unknown directive: " + Tok);
     }
   }
if (!Cmd) {
         Cmd = new AssertCommand(readAssert());
       else
         Cmd = readOutputSectionDescription(Tok);
     }
     Opt.Commands.emplace_back(Cmd);
   }
 }
 
+void ScriptParser::readStartup() { Config->Startup = readParenLiteral(); }
+
 static int precedence(StringRef Op) {
   return StringSwitch<int>(Op)
       .Cases("*", "/", 5)
       .Cases("+", "-", 4)
       .Cases("<<", ">>", 3)
       .Cases("<", "<=", ">", ">=", "==", "!=", 2)
       .Cases("&", "|", 1)
       .Default(-1);

test/ELF/linkerscript/startup.s

+# REQUIRES: x86
+
+# RUN: mkdir -p %t.dir
+# RUN: cd %t.dir
+
+# RUN: echo ".quad 0xAAAAAAAAAAAAAAAA" > %t1.s
+# RUN: echo ".quad 0xFFFFFFFFFFFFFFFF" > %t2.s
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %t1.s -o foo.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %t2.s -o bar.o
+
+# RUN: echo "STARTUP(foo.o)" > script
+# RUN: ld.lld -o exe -script=script foo.o bar.o
+# RUN: llvm-objdump -s exe | FileCheck -check-prefix=FOO %s
+
+# FOO: Contents of section .text:
+# FOO: 201000 aaaaaaaa aaaaaaaa ffffffff ffffffff
+
+# RUN: echo "STARTUP(bar.o)" > script
+# RUN: ld.lld -o exe -script=script foo.o bar.o
+# RUN: llvm-objdump -s exe | FileCheck -check-prefix=BAR %s
+
+# BAR: Contents of section .text:
+# BAR: 201000 ffffffff ffffffff aaaaaaaa aaaaaaaa
+
+# RUN: echo "STARTUP(nosuchfile)" > script
+# RUN: ld.lld -o exe -script=script foo.o bar.o 2>&1 \
+# RUN:   | FileCheck -check-prefix=WARN %s
+
+# WARN: nosuchfile: STARTUP file not found