Do not call exit() directly from lld.

[ruiu]

Summary

Our promise is that as long as there's no fatal error (i.e. broken
file is given to the linker), our main function returns to the caller.
So we can't use exit() in the regular code path.

[rdhindsa]

If we use return (instead of exit) as in this patch, the final params file( Config->ThinLTOIndexOnlyObjectsFile) is not fully generated and few of the last entries are not written(even though respective files are generated) . Here _exit() is called eventually from exitLld function call in elf::link . However, if we replace that with exit(), the file is generated properly. From here, it seems that _exit() is not able to close the file properly.

[ruiu]

_exit() doesn't flush the buffer indeed. So it is likely that the LTO object holds file handles until it is destroyed. Maybe we should call the destructor before returning. Let me try that.

Do you know how I can test it?

[ruiu]

• flush IndexFile before returning so that the file is not truncated.

[pcc]

LGTM

ELF/Driver.cpp

template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   // name "foo@ver1") rather do harm, so we don't call this if -r is given.
   if (!Config->Relocatable)
     Symtab->scanVersionScript();
 
   // Create wrapped symbols for -wrap option.
   for (auto *Arg : Args.filtered(OPT_wrap))
     Symtab->addSymbolWrap<ELFT>(Arg->getValue());
 
+  // Do link-time optimization if given files are LLVM bitcode files.
+  // This compiles bitcode files into real object files.
   Symtab->addCombinedLTOObject<ELFT>();
   if (errorCount())
     return;
 
+  // If -thinlto-index-only is given, we should create only "index
+  // files" and not object files. Index file creation is already done
+  // in addCombinedLTOObject, so we are done if that's the case.
+  if (Config->ThinLTOIndexOnly)
+    return;
+
   // Apply symbol renames for -wrap.
   Symtab->applySymbolWrap();
 
   // Now that we have a complete list of input files.
   // Beyond this point, no new files are added.
   // Aggregate all input sections into one place.
   for (InputFile *F : ObjectFiles)
     for (InputSectionBase *S : F->getSections())

ELF/LTO.cpp

for (LazyObjFile *F : LazyObjFiles) {
       ModuleSummaryIndex M(false);
       M.setSkipModuleByDistributedBackend();
       WriteIndexToFile(M, *OS);
     }
 
     // ThinLTO with index only option is required to generate only the index
     // files. After that, we exit from linker and ThinLTO backend runs in a
     // distributed environment.
-    exit(0);
+    if (IndexFile)
+      IndexFile->close();
+    return {};
   }
 
   for (std::unique_ptr<MemoryBuffer> &File : Files)
     if (File)
       Ret.push_back(createObjectFile(*File));
   return Ret;
 }

test/ELF/lto/thinlto.ll

 ; IN1: {{.*}}thinlto.ll.tmp.o
 ; IN1-NEXT: {{.*}}thinlto.ll.tmp2.o
 ; IN1-NEXT: {{.*}}thinlto.ll.tmp4.o
 
 ; Ensure lld generates error if unable to write to index file
 ; RUN: rm -f %t4.o.thinlto.bc
 ; RUN: touch %t4.o.thinlto.bc
 ; RUN: chmod 400 %t4.o.thinlto.bc
-; RUN: ld.lld -m elf_x86_64 --plugin-opt=thinlto-index-only -shared %t.o %t4.o -o %t5 2>&1 | FileCheck %s --check-prefix=ERR
+; RUN: not ld.lld -m elf_x86_64 --plugin-opt=thinlto-index-only -shared %t.o %t4.o -o %t5 2>&1 | FileCheck %s --check-prefix=ERR
 ; ERR: cannot open {{.*}}4.o.thinlto.bc: {{P|p}}ermission denied
 
 ; Ensure lld doesn't generates index files when thinlto-index-only is not enabled
 ; RUN: rm -f %t.o.thinlto.bc
 ; RUN: rm -f %t2.o.thinlto.bc
 ; RUN: rm -f %t4.o.thinlto.bc
 ; RUN: ld.lld -m elf_x86_64 -shared %t.o %t2.o %t4.o -o %t5
 ; RUN: not ls %t.o.thinlto.bc