[ELF] Don't warn about missing start symbol in relocatable and shared files

[phosek]

Summary

Previously LLD would print a warning for missing entry symbol in relocatable and shared output files, which is incorrect as these normally don't have an entry symbol.

[davide]

Did you try gold/bfd and see how they behave?

[phosek]

This comment was removed by phosek.

[phosek]

Yes, neither of them emits the warning. This was actually discovered while linking an existing code which relies heavily on relocatable objects where BFD ld and gold are both silent but LLD would emit a lot of warnings.

[davide]

I think this one is OK. Please wait for Rafael sign-off as he introduced the feature (and the warning)

[ruiu]

ELF/Driver.cpp

679

HasEntry and HasEntryAddr seem a bit confusing here. I think you only had to change this line to

if (!HasEntryAddr && !Config->Entry.empty()) {

no?

[emaste]

Also http://llvm.org/pr30521

[phosek]

I'm happy to to let George land his change https://reviews.llvm.org/D24913 and abandon this one if you prefer his solution.

[ruiu]

Yeah, I didn't notice until now that his change is exactly what I suggested. I'll LGTM his change.

[phosek]

Abandoned in favor of https://reviews.llvm.org/D24913.

[grimar]

Thanks, Petr and sorry I really did not notice you're already working on this, just was trying to fix unassigned PR30521 :]

[• rafael]

This LGTM with "HasEntry" rename something like "EntrySymbolExpected"

ELF/Driver.cpp

template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   // 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.
+  const bool HasEntry =
+    !Config->Shared && !Config->Relocatable && Config->EMachine != EM_AMDGPU;
   bool HasEntryAddr = false;
   if (!Config->Entry.empty()) {
     // It is either "-e <addr>" or "-e <symbol>".
     HasEntryAddr = !Config->Entry.getAsInteger(0, Config->EntryAddr);
-  } else if (!Config->Shared && !Config->Relocatable &&
-             Config->EMachine != EM_AMDGPU) {
+  } else if (HasEntry) {
     // -e was not specified. Use the default start symbol name
     // if it is resolvable.
     Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
   }
   if (!HasEntryAddr) {
     if (Symtab.find(Config->Entry))
       Config->EntrySym = Symtab.addUndefined(Config->Entry);
-    else
+    else if (HasEntry)
       warning("entry symbol " + Config->Entry + " not found, assuming 0");
   }
 
   if (HasError)
     return; // There were duplicate symbols or incompatible files
 
   Symtab.scanUndefinedFlags();
   Symtab.scanShlibUndefined();

test/ELF/driver.test

 ## "--output=foo" is equivalent to "-o foo".
 # RUN: not ld.lld %t --output=/no/such/file 2>&1 | FileCheck -check-prefix=ERR7 %s
 # ERR7: failed to open /no/such/file
 
 ## "-output=foo" is equivalent to "-o utput=foo".
 # RUN: not ld.lld %t -output=/no/such/file 2>&1 | FileCheck -check-prefix=ERR8 %s
 # ERR8: failed to open utput=/no/such/file
 
+## Do not report warning about missing entry symbol for -r
+# RUN: ld.lld -r %t -o %tsuccess 2>&1 | FileCheck -allow-empty -check-prefix=ERR9 %s
+# ERR9-NOT: entry symbol not found, assuming 0
+
 .globl _start
 _start:
   nop